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- Large Volume Sample Introduction Using Temperature Programmable Injectors: Implications of Liner Diameter.
<< Read Abstract >>
Temperature programmable injectors with liner diameters ranging from 1 to 3.5 mm are evaluated and compared for solvent split injection of large volumes in capillary gas chromatography. The liner dimensions determine whether a large sample volume can be introduced rapidly or has to be introduced in a speed controlled manner. The effect of the injection technique used on the recovery of n-alkanes is evaluated. Furthermore the influence of the liner diameter on the occurrence of thermal degradation during splitless transfer to the analytical column is studied. Guidelines are given for the selection of the PTV liner internal diameter best suited for specific applications.
- Large Volume Injection in Capillary GC Using PTV Injectors: Comparison of Inertness of Packing Materials.
- Recent improvements in high-temperature PTV injection for high-temperature capillary gas chromatography.
American M.P.M. van Lieshout, H.-G. Janssen and C.A. Cramers, Laboratory, August 1995, 38-44
- Simulated Distillation Using a Mid-Polarity Capillary Column.
Allen K. Vickers, Mike D'Amico and Phil Stremple, J&W Scientific, Pittcon '96 Presentation
- Characterization of Polymers by Multi-Step Thermal Desorption/Programmed Pyrolysis Gas
Chromatography Using a Hign Temperature PTV Injector.
M. van Lieshout, M.J.J. Hetem. Journal of High Resolution Chromatography, 19 (1996) 193-199<< Read Abstract >>Thermal treatment hyphenated with gas chromatography is a versatile and powerful tool in the study of polymer characterization. An inexpensive system where thermal treatment at different temperatures occurs inside a Programmable Temperature Vaporization injector (PTV) is described. The samples investigated, commercial plastics, are complex mixtures that contain several polymers and additives. These plastics as well as their pure constituents are subjected to multi-step thermal treatment. The individual chromatograms of the various constituents of the polymeric sample are correlated with those of the final material in order to identify additives (thermal desorption) and degradation products (pyrolysis). Results obtained with the new method indicate the interesting potentials of the technique for the characterization of polymer compositions. Reproducibility of absolute and relative peak areas has been considered and found to be acceptable. The absence of a heated transfer line and switching valves, which are always present in conventional set-ups, eliminates the risk of losses of high molecular weight components. Further advantages of the technique proposed are simplicity, versatility, and its inexpensive nature.
- Environmental Applications of Large Volume Injection in Capillary GC using PTV Injectors.
H.G.J. Mol, Journal of High Resolution Chromatography, Vol 19 (1996)69-79<< Read Abstract >>Temperature programmable (PTV) injectors with packed widebore (ca. 3.5 mm i.d.) liners are used for large volume injection in capillary gas chromatography with the aim to simplify and/or improve off-line sample pretreatment proecdures. A simple procedure for optimization of large volume PTV injection is described. The system performance, i.e. linearity and repeatability, is evaluated for polar nitrogen/phosphorus containing pesticides (PTV-GC-NPD) and organochlorine pesticides (PTV-GC-ECD) in river water extracts as well as for polycyclic aromatic hydrocarbons (PAHs) in river sediment (PTV-GC-MS).
- A Simplified Method for the Determination of Atmospheric Hydrocarbons.
K.D. Bartle and A.C. Lewis, LC-GC International (May 1996) 297-304<< Read Abstract >>An instrument has been developed for the automated in situ determination of airborne C1-C6 and C6-C12 volatile organic compounds using programmed temperature vaporisation (PTV) injection from a sorbent tube trap. A single sorbent tube placed as an injection port liner in a sub ambiently cooled PTV, can be repeatedly used to collect samples of air, with the trapped analytes being subsequently desorbed direct onto either a wide bore 100 % dimethyl polysiloxane (C6-C12) or porous layer Al2O3 Na2SO4 doped open tubular (C1-C6) gas chromatography column without use of intermediate cryogenic refocussing. High flow rates of helium used during the analysis result in not only a rapid and optimal separation, but also a fast recleaning of the sorbent tube making it ready to reuse following the analytical separation, with a lifetime of many hundreds of cycles. Using 30 - 60 mesh activated charcoal as an adsorbent (C1-C6), breakthrough volumes of ethane were determined to be over 1 Litre. Desorption at 400 °C made the use of this type of trap for compounds as large as toluene possible. Using Tenax TA adsorbent (C6-C12), breakthrough volumes for most C6 compounds were found to be over 5 Litres, well in excess of the sample volume needed to quantify VOC concentrations in ambient air. Detection was via parallel FID/ECD, with limits for individual compounds in a 1 Litre air sample of around 5-30 pptV dependant on detector response. Methane cannot be quantifiably trapped onto activated charcoal, however owing to the high concentration of methane in the atmosphere (around 2 ppmV), a quantifiable response is observed on the chromatogram proportional to the internal volume of the injector port. This provides a new method for methane detection using existing equipment, which cannot be achieved when an intermediate cryofocusing step is used. Examples of analysis of a wide range of both urban and rural ambient hydrocarbons are presented demonstrating the possibility to quasi-continuously monitor concentrations of VOCs in locations where high sensitivity continuous in situ analysis is required, but where cryogenic coolants may not be readily available or desirable.
- Large Volume Injection in Gas Chromatographic Trace Analysis Using Temperature Programmable (PTV) Injectors.
Hans G J Mol, Hans-Gerd Janssen, Carel A Cramers & Udo A Th Brinkman Trends in Analytical Chemistry, 15 4 (1996) 206-214<< Read Abstract >>The use of programmed-temperature vaporising (PTV) injectors for large-volume injection in capillary gas chromatography is briefly reviewed. The principles and optimisation of large-volume PTV injection are discussed. Guidelines are given for selection of the PTV conditions and injection mode for specific applications. Relevant examples from the recent scientific literature serve as illustrations.
- Atmospheric Monitoring of Volatile Organic Compounds Using Programmed Temperature Vaporisation Injection.
A.C. Lewis, P.W. Seakins, K. D. Bartle, Journal of High Resolution Chromatography 19 (1996) 686-690<< Read Abstract >>A method has been developed for the automated determination of C5-C10 and C2-C6 volatile organic compounds in urban and rural air, using programmed temperature vaporization injection from a sorbent tube trap. A single activated charcoal sorbent tube was repeatedly used to collect samples of air with trapped VOCs being subsequently desorbed onto either a wide bore dimethyl polysiloxane (C5-C10) or porous layer open tubular (C2-C6) gas chromatography column without use of intermediate cryogenic refocussing. The high flow rates of helium used during the analysis resulted in the sample tube being cleaned and ready to reuse following the analytical separation. Examples of analysis of aromatic VOCs in urban air, and biogenic emissions in rural air, collected in a Sitka Spruce forest are presented. Using this method it is possible to quasi-continuously monitor concentrations of VOCs in locations where high sensitivity in situ analysis is required, but where cryogenic coolants may not be readily available or desirable.
- Programmed-temperature vaporiser injector as a new analytical tool for combined thermal desorption-pyrolysis
of solid samples. Application to geochemical analysis.
M. van Lieshout, G.A. van den Bos, Journal of Chromatography A, 764 (1997) 73-84<< Read Abstract >>This paper describes a new analytical tool for the analysis of geological samples for geochemical purposes. A system is described that allows subsequent thermal treatment at several stages to occur inside the liner of a programmed temperature vaporiser injector (PTV). The samples under investigation are geological hydrocarbon source rock and coal samples. Analysis of the samples is performed in a sequential procedure. A three-step temperature-level procedure is proposed. The system described is inexpensive and easy to operate. The advantage of combining thermal desorption and pyrolysis sequentially inside a PTV injector is the flexibility of temperature selection, as well as the ease of calibration and quantitation. Moreover, the absence of a heated transfer line and heated valves minimises the risk of loss of high-molecular-mass compounds. The method described allows a detailed characterisation of oil and kerogen in a source rock. An atomic emission detector is used to monitor simultaneously the carbon and the sulphur signals for further structural elucidation of the kerogen. The results obtained with this system are in good agreement with those obtained with other pyrolysis systems.
- Quantitative Aspects of Comprehensive Two-Dimensional Gas Chromatography (GC6GC)
Jan Blomberg, Jan Beens, Hans Boelens, Robert Tijssen, J. High Resol. Chromatogr., Vol. 21, January 1998<< Read Abstract >>A software program was developed to enable the quantification of the complex 3D-data sets as produced by GCxGC. Using this software, it was demonstrated that the detectability limit of GCxGC in our study is 18 times better than that of ’normal’ capillary gas chromatography (CGC). This enhancement is due to the signal increase produced by the thermal modulation effect. The relative standard deviation of 0.9% as measured on a test mixture was excellent. Furthermore, a comparison was made for the group-type separation of heavy gas oils between the hyphenation of LC and GC (LC-GC) and GCxGC. Although these separations are different in nature, the agreement of the results of both methods was very good. The results of GCxGC may even be more accurate, since, different from CGC, even in the most complex chromatograms the baseline in the second dimension chromatograms is always present.
- Determination of triazine pesticedes in tap water by SPE-GC/MS
- A VISION to On-Line SPE-PTV-GC-MS Determination of Organic Micro Pollutants in Surface Water.
Sjaak de Koning, Mark van Lieshout, Hans-Gerd Janssen, Wil van Egmond.
- Coupling devive for desorption of drugs from solid-phase extraction-pipette tips and on-line gas chromatographic analysis.
M.W.J. van Hout, R.A. de Zeeuw, G.J. de Jong, Journal of Chromatography A, 858 (1999) 117-122<< Read Abstract >>Solid-phase extraction-pipette tips were used for micro solid-phase extraction of lidocaine and diazepam. Off-line desorption was done after in-vial collection for reference purposes, whereas with on-line desorption the eluate was directly introduced in the gas chromatograph. With both methods the total eluate (100 µl) was introduced into the GC system, which was equipped with a programmed-temperature vaporiser (PTV) for large volume injection. For on-line desorption a laboratory-made coupling device was developed to connect the pipette tips with the injector of the PTV. The coupling device was applied successfully since no leakage occurred at the connection of the coupling device and the pipette tip. No significant differences in recovery of lidocaine and diazepam and in presence of impurities were observed between chromatograms obtained with either off-line or on-line desorption. Preliminary experiments with standard solutions showed recoveries of about 75% for a concentration level of 1 µg/ml. The system seems particularly suitable for high-throughput analysis.
- Evaluation of the Programmed Temperature Vaporiser for Large Volume Injection of Biological Samples in Gas Chromatography.
M W J van Hout, R A de Zeeuw, J P Franke & G J de Jong. Journal of Chromatography B. 729 (1999) 199-210<< Read Abstract >>The use of a programmed temperature vaporiser (PTV) with a packed liner was evaluated for the injection of large volumes (up to 100 µl) of plasma extracts in a gas chromatograph. Solvent purity, which is essential when large volumes are injected into the GC system, was determined. Special attention was paid to the purity of the solvents used for the solid-phase extraction (SPE) procedure. For this SPE method, ethyl acetate was used as the extraction and reconstitution solvent, and thus the purity of the ethyl acetate was critical, especially when a non-selective GC detector was applied. The liquid capacity and inertness of different packed liners were investigated. The liner packed with ATAS A (modified Chromosorb-based material with special treatment) was found to be the most suitable for the analysis of the tested drugs. Good linearity in response for variations in volume and concentration was observed. A comparison was made between the applicability of flame ionisation detection (FID) and mass-selective detection (MSD). When 50 µl volumes of plasma extracts were injected with the PTV, the detection limits for secobarbital, lidocaine, phenobarbital and diazepam were about 50-times lower than when 1 µl volumes were injected. The detection limits of the tested compounds in plasma for injection of 50-100 µl plasma extract are 5-10 ng/ml for GC-FID whereas plasma concentrations of 250 pg/ml can be detected using the selected ion monitoring (SIM) mode of a MSD. For non-selective GC-FID, the background from a 50 µl injection was substantially larger than with 1 µl injection as a result of co-injected plasma matrix components and solvent impurities. These background effects were less with GC-MSD in the total ion current mode and virtually absent with GC-MSD in the SIM mode.
- Programmable Temperature Vaporization interface for on-line trace-level enrichment - GC-MS of micropollutants in surface water.
Sjaak De Koning, Mark van Lieshout, Hans-Gerd Janssen, Udo A. Th. Brinkman. Journal of Microcolumn Separations, volume 12 issue 3, 2000. pages: 153-159<< Read Abstract >>In the present study, a fully automated solid-phase extraction (SPE) system, a programmed temperature vaporization (PTV) interface, and gas chromatography (GC) with mass spectrometric (MS) detection are combined for the trace-level analysis of micropollutants in surface water. The PTV interface is selected because of its reliability regarding large volume injection and its robustness when analyzing real-life samples. The mass spectrometer was used both in the full-scan and the selected ion monitoring modes and gave detection limits of about 15-40 ng/L and 0.7-5 ng/L (7.5-mL samples), respectively, for a series of NP-pesticides.
- On-line coupling of solid-phase extraction to gas chromatography with fast solvent vaporizing and concentration in an open injector liner. Analysis of pesticidus in equeous samples.
R. Sasano, T. Hamada, M.Kurano, M. Furuno. Journal of Chromatography A VOL. 896, 2000, 41-49<< Read Abstract >>The purpose of this study is to combine solid-phase extraction (SPE) with gas chromatography (GC) for the fully automated determination of pesticides and herbicides in aqueous samples. The interface technique employed for connecting SPE with GC was fast solvent vaporization and concentration in an open injector liner. The interface device consisted of the programmed-temperature vaporizing injector without using the packing material in the liner and the target compounds were concentrated around the inlet of the GC capillary column. This avoided the degradation of target compounds, and no precise control of the injecting speed was required, when an automatic SPE system was connected to GC-MS. The aqueous samples used in this system were prepared by spiking 29 kinds of pesticide and herbicide compounds, which are regulated by the Ministry of Health and Welfare of the Japanese National government, in purified water and river water, to a resulting concentration of 1 µg/l. Employing this system, the recoveries and RSDs (n=6) of most compounds were greater than 75% and within 10%, respectively. From the results of this study, we found that on-line automatic SPE and capillary GC-MS equipped with the fast solvent vaporizing and concentrating method in an open injector liner could be connected in order to obtain good results for the determination of pesticides in water samples.
- Miniaturised pressurised liquid extraction of polycyclic aromatic hydrocarbons from soil and sediment with subsequent large-volume
L. Ramos, J.J. Vreuls, U.A.Th. Brinkman. Journal of Chromatography A, 891 (2000) 275-286<< Read Abstract >>Analyte extraction is the main limitation when developing at-line, or on-line, procedures for the preparation of (semi)solid environmental samples. Pressurised liquid extraction (PLE) is an analyte- and matrix-independent technique which provides cleaner extracts than the time-consuming classical procedures. In the study, the practicality of miniaturised PLE performed in a stainless-steel cell, and combined with subsequent large-volume injection (LVI)-GC-MS was studied. As an example, the new system was applied to the determination of polycyclic aromatic hydrocarbons (PAHs) in soils and a sediment. Variables affecting the PLE efficiency, such as pressure and temperature of the extraction solvent and total solvent volume, were studied. Toluene was selected as extraction solvent and a total solvent volume of 100 µl was used for the 10 min static-dynamic PLE of 50-mg samples. Additional clean-up or filtration of the sample extracts was not required. Detection limits using LVI-GC-MS were below 9 ng/g soil for the 13 PAHs more volatile than indeno[1,2,3-cd]pyrene in real soil samples and the repeatability of the complete PLE plus LVI-GC-MS method for the analysis of the endogenous PAH was better than 15%. Comparison of PLE and Soxhlet or liquid-partitioning extraction results for the analysis of non-spiked samples showed that the efficiency of PLE is the same or better than for the other two extraction methods assayed.
- Automation of the GM-MS analysis of mineral oil contaminations in water
O. Lerch, P. Zinn, H.J. Götze. Fresenius J. Anal. Chem. (2000) 267 : 195-200.
- Inlet derivatization for the GC analysis of organic acid mixtures
T. P. Lynch and A. P. K. Grosser CAST, Chromatogr. Sep. Technol., 2000(13), 12-15<< Read Abstract >>The procedure employed an Optic 200 PTV injector installed on a Chrompack CP9001 gas chromatograph with FID detection. The injector was fitted with a liner packed with Supelcoport. The reactants were injected into the liner under stopped flow conditions at 45°C and the temperature was then increased at 16°C/s to 250°C (held for 2 min). A pressure pulse was then used to transfer the reaction products into the column for analysis. The procedure was performed using 850µl portions of process stream samples (for acetic acid production) containing succinic acid and laevulinic acid in THF to which 350µl of the derivatizing reagent [bis(trimethylsilyl)trifluroacetamide] was added. A 1 µl portion of the resulting mixture was injected into the PTV inlet for derivatization to the silyl ester to occur. The calibration graphs for succinic acid and laevulinic acid were linear over the ranges: 50-100% and 0-10%, respectively, and regression coefficients were 0.9993 and 0.9998, respectively.
- Direct injection of human plasma samples after ultrafiltration into programmed temperature vaporiser-gas chromatography-mass spectrometry with packed liner.
Mohamed Abdel-Rehim, Karin A. Svensson, Yvonne Askemark, Karl-Johan Pettersson. Journal of Chromatography B, 755 (2001) 253-258<< Read Abstract >>The direct injection of plasma samples after ultrafiltration into a gas chromatograph using a packed injector liner was investigated. Ropivacaine, a local anaesthetic of the amide type and one of its metabolites (PPX) were used as model compounds in this evaluation. Phosphoric acid was added to the plasma to minimize the protein binding. After ultrafiltration, 50 µl of the sample was directly injected into the chromatographic system. No interfering peaks or damage to the GC or MS system were observed using ultrafiltration as a sample-preparation method. The validation of the method demonstrated good linearity and selectivity. The limits of quantification were 1.1 nM (301 pg/ml) and 1.4 nM (325 pg/ml) for ropivacaine and PPX, respectively. The liner had to be changed after 20 injections.
- Application of solid-phase extraction and rapid, large-volume injection for routine analysis of evironmental samples via U.S.
EPA SW-846 Method 8270D.
Daniel P.Dodson and Robert S. Johnson. American Laboratory News, April 2001
- Miniaturized automated matrix solid-phase dispersion extraction of pesticides in fruit
followed by gas chromatographic-mass spectrometric analysis.
E. Maria Kristenson, Esther G.J. Haverkate, Cees J. Slooten, Lourdes Ramos, René J.J. Vreuls, Udo A. Th. Brinkman. Journal of Chromatography A, 917 (2001) 277-286<< Read Abstract >>In this study a simple and fast miniaturized automated matrix solid-phase dispersion method for the sample preparation and quantitative extraction of pesticides was developed and evaluated. Only 25 mg of sample and 100 µl of organic solvent were used per analysis for this new miniaturized set-up. The extracts were subsequently analysed by GC-MS without any further purification. The method was optimized for oranges and tested for the determination of a variety of organophosphorus pesticides and a pyrethroid at concentration levels below the maximum residue levels set by the European Union and authorities in The Netherlands. The limits of detection were 4-90 µg/kg. The recoveries for pesticides in orange were 83-118% and the relative standard deviations for the total procedure were 10-13% (n=4) at the limit of quantification. The feasibility of the developed method for apple, pear and grapes was also studied. Equally good results were obtained, but for apple the washing step should be omitted.
- Use of a PTV injector to achieve inverse-large volume injection: injection of volatile analytes in a semi-volatile solvent.
Journal of Separation Science, 2001, 24, 291-296<< Read Abstract >>Large volume injection of volatile analytes in a semi-volatile solvent, termed inverse-LVI, has been accomplished using a programmable-temperature vaporizing (PTV) injector. It was found that simple optimization of the time the split valve remained closed allowed complete analyte transfer to the column, while venting most of the solvent. Increasing the PTV temperature ramp from 10 K/s to 15 K/s was found to improve peak shapes, especially of the early eluting peaks, by decreasing the injection bandwidth. In addition, the optimum splitless time was found to be independent of injection volume (up to solvent limits) meaning only a single optimization was necessary for quantitative analyte transfer from each solvent. The ability to quantitatively transfer the analyte to the column was also found to be solvent independent (propylene carbonate, tridecane, and Butyl CARBITOL® Solvent were evaluated). Excellent data were obtained for injection volumes up to 15 µL of propylene carbonate and 36 µL of tridecane using an unpacked fritted PTV liner.
- Automated determination of fatty acid methyl ester and cis/trans methyl ester composition of fats and oils.
Sjaak de Koning, Bram van der Meer, Geert Alkema, Hans-Gerd Janssen, Udo A.Th. Brinkman. Journal of Chromatography A, 922 (2001) 391-397<< Read Abstract >>The determination of the fatty acid composition (as methyl esters, FAMEs) of fats and oils and their cis/trans (CTME) distribution requires a simple, but manual and time-consuming sample preparation. The so-called BF3 method is often the preferred procedure. Because FAME/CTME analyses are encountered very frequently in the food industry, an automated, robot-based alternative is proposed which uses the sodium methylate procedure. After sample weighing and the (manual) addition of heptane (2 min), a XYZ robotic autosampler is used for all remaining work, which includes reagent addition, agitation, sample settling and the final injection into the gas chromatograph (10 min). The performance of the sodium methylate and BF3 methods are compared by analysing some 30 oil and fat samples. The novel procedure is much faster (less than 15 min versus ca. 1 h) and manual sample handling is drastically decreased. The experimental results obtained with the two methods frequently are the same, while small differences can be explained by (known) differences of the two methods in the conversion of minor oil/fat constituents, such as free fatty acids, wax esters and sterol esters. In case of FAME analyses, a hot injection is to be preferred over a cold injection. The RSDs of the peak areas were 1.5% for the major fatty acids to 11% for peaks that were just above the noise level. The detection limit were approximately 0.03%.
- Feasibility of the direct coupling of solid-phase extraction-pipette tips with a programmed-temperature vaporiser for gas chromatographic analysis of drugs in plasma.
M.W.J. van Hout, W.M.A. van Egmond, J.P. Franke, R.A. de Zeeuw, G.J. de Jong. Journal of Chromatography B, 766 (2002) 37-45<< Read Abstract >>Solid-phase extraction-pipette tips (SPE-PTs) were used for micro solid-phase extraction of lidocaine and diazepam from plasma. Off-line extraction was followed by on-line desorption. On-line desorption was carried out by direct coupling of the SPE-PTs with the liner of the programmed-temperature vaporiser. This coupling only required shortening of the liner by maximally 16 mm, cutting the SPE-PT, and equipping the remaining part with two O-rings. Due to the heating of the injector the SPE-PTs were heated as well, which resulted in a significant amount of impurities. Pre-heating and pre-washing was performed prior to the extraction to reduce the impurity level. The internal coupling device was applied successfully for the analysis of plasma samples with gas chromatography (GC) and mass-selective detection. Detection limits of 0.75 ng/ml and 2.5 ng/ml were obtained for lidocaine and diazepam, respectively, using 200 µl plasma. Recoveries for both compounds were about 80%. Although it is possible, the internal coupling device was not developed to be used as such. The main goal of this coupling was to show the feasibility of the integration of SPE-PTs with GC and to realize an important step to new automated SPE-GC systems.
- Pestizidanalytik in trauben mit LV-DTD/DMI-GC/TOF-MS.
LaborPraxis Dec. 2002.
- Analyses of the wood preservative component N-cyclohexyl- diazeniumdioxide in impregnated pine sapwood by direct thermal desorption-gas chromatography-mass spectrometry.
Jüngel, P.; De Koning, S.; Brinkman, U. A. T.; Melcher, E.: Journal of Chromatography A, Amsterdam 953 (2002) S. 199-205.<< Read Abstract >>Investigations concerning the qualitative and quantitative determination of the organic wood preservative component N-cyclohexyl-diazeniumdioxide (HDO) in treated timber were carried out by means of direct thermal desorption-gas chromatography-mass spectrometry (DTD-GC-MS). It could be shown that the identification of HDO in treated pine sapwood (Pinus sylvestris L.) is relatively simple using this analytical technique. Quantification of this active ingredient can be carried out using the peak area of the specific mass fragment m/z 114. A calibration curve with a high correlation coefficient was obtained in the range from 40 to 550 mg HDO per kg timber. Furthermore it can be deduced that the results obtained are characterised by an excellent reproducibility with standard deviations ranging from 5 to 10% in general. For the chosen experimental set up a detection limit of 4 mg HDO per kg treated pine sapwood was calculated, although merely 20% of the active ingredient was desorbed.
- Automated liner exchange - A novel approach in direct thermal desorption-gas chromatography.
De Koning, J.A.; Blokker, P.; Jüngel, P.; Alkema, G.; Brinkman U. A.T.: Chromatographia, Wiesbaden 56 (2002) S. 185-190.<< Read Abstract >>A system was developed for fully automated liner exchange in direct thermal desorption- gas chromatography- mass spectrometry (DTD-GC-MS). Samples are put into a newly developed liner which is capped with a standard crimp cap. The liners are placed in a sample tray and transported to the thermal desorption device. Both liner transport and liner exchange (which can be performed after each analysis) are automated. The system was tested for spores and pollen, vegetable oil, wood (preservative), car exhaust (BTEX), and tobacco (nicotine) analysis to demonstrate the robustness and flexibility of the approach.
- At-line gas chromatographic-mass spectrometric analysis of fatty acid profiles of green microalgae using drect thermal desorption interface.
P. Blokker, R. Pel, L. Akoto, U.A.T. Brinkman, R.J.J. Vreuls. J. Chromatogr. A 959 (2002) 191-201.<< Read Abstract >>Thermally assisted hydrolysis and methylation-gas chromatography (THM-GC) is an important tool to analyse fatty acid in complex matrices. Since THM-GC has major drawbacks such as isomerisation when applied to fatty acids in natural matrices, a direct thermal desorption (DTD) interface and an incubation time of 30 min were used to circumvent these problems. Using vegetable oils such as sunflower oil and triarachidonin, the conversion of triglycerides into their fatty acid methyl esters (FAMEs) was investigated. The yields using a DTD (and trimethylsulfonium hydroxide as a reagent) were found to be similar or even higher than when applying a conventional off-line method, while the FAME profiles were identical. When the procedure was applied to analyse the FAME profiles of microbial cells in a methanolic or aqueous suspension, it was found that accurate profiles are obtained for such samples. Thus, the present approach opens the route to analyse fatty acids in microbial cells in a fully automated fashion, which will allow high sample throughput.
- Trace-level determination of pesticides in food using difficult matrix introduction-gas chromatography-time-of-flight mass spectrometry
Sjaak de Koning, Gunter Lach, Manfred Linkerhagner, Ralf Loscher, Peter Horst Tablack, Udo A. Th. Brinkman. Journal of Chromatography A, 1008 (2003) 247-252<< Read Abstract >>A procedure for the fully automated analysis of food samples by means of difficult matrix introduction-gas chromatography-time-of-flight mass spectrometry (DMI-GC-ToF MS) is discussed. After extraction, samples require very little clean-up and are injected in a micro- or µ-vial which is held in a liner. Next, the liner is placed in the injector and the contents of the vial are thermally desorbed and led directly to the capillary GC column. After GC-ToF MS analysis, the data are processed automatically using a peak deconvolution algorithm. The practicability of the procedure was demonstrated by analysing spiked grape and pineapple samples down to the 1-10 ng/g concentration level.
- Analysis of pesticide residues in lettuce by large volume-difficult matrix introduction-gas chromatography-time of flight-mass spectrometry
Katan Patel, Richard J. Fussell, David M. Goodallb and Brendan J. Keely Analyst, 2003, 128, 1228-1231<< Read Abstract >>A multi-residue method is described that eliminates the need for a clean-up step and thus allows the rapid determination of pesticides in crude extracts of lettuce. Samples were extracted with a mixture of ethyl acetate, Na2SO4 and NaHCO3 and the crude extracts analysed directly using large volume-difficult matrix introduction (LV-DMI) in combination with gas chromatography-time of flight-mass spectrometry (GC-TOF-MS). The LV-DMI procedure described was evaluated for the analysis of dimethoate, pyrimethanil, chlorothalonil, vinclozolin, furalaxyl and oxadixyl. Satisfactory response was obtained at the lowest calibrated level (LCL) of 0.0025 µg ml-1, with good linearity over the range 0.0025-0.5 µg ml-1(0.005-1.0 mg kg-1 equivalent). Average recoveries between 73 and 118% were obtained at the 0.01-0.5 mg kg-1 levels with RSD values 13%.
- AT-column, a novel concentrating technique for large-volume injections in gas chromatography
Sjaak de Koning, Mitsuhiro Kurano, Hans-Gerd Janssen, Udo A.Th. Brinkman. Journal of Chromatography A, 1023 (2004) 165-174<< Read Abstract >>Nowadays, large-volume injection is widely used for the GC determination of trace analytes, specifically to improve detectability. The most popular injectors for large-volume injections are the programmable temperature vaporisation (PTV) injector and the cold on-column (COC) injector, where each device has its own advantages and limitations. The novel AT-column concentrating technique combines features of two other injection techniques, loop-type large-volume and vapour overflow. AT-column injection is based on solvent evaporation in an empty liner with solvent vapour discharge via the split line. Little or no optimisation is required. The only relevant parameter is the injection temperature which can easily be calculated using the equation of Antoine. As an application, AT-column injection is combined with GC-MS for the trace-level determination of labile analytes and with GC-flame ionisation detection for the analysis of high molecular weight polymer additives. In summary, AT-column is an injection technique that combines the inertness of the COC, and the flexibility and robustness of the PTV large-volume technique.
- Automated on-line comprehensive two-dimensional LCxGC and LCxGC-ToF MS: Instrument design
and application to edible oil and fat analysis
Sjaak de Koning, Hans-Gerd Janssen, Marieke van Deursen, Udo A.Th. Brinkman. Journal of Separation Science 2004, 27, 397-409<< Read Abstract >>After a successful off-line feasibility study, the automation of comprehensively coupled liquid chromatography and gas chromatography (LCxGC) has been studied. Important aspects to consider when developing automated LGxGC include the relative speeds of the two dimensions, the compatibility of the LC eluent (type and flow rate) with the GC dimension, and the column loadabilities. Because the GC separation is relatively slow, the LC instrument has to be operated in the stop-flow mode. Two interfaces for transferring large numbers of subsequent LC fractions to the GC were constructed: one based on a six-port switching valve, and one which uses a dual side-port syringe. Both interfaces were found to perform fully acceptably. The actual transfer of the LC fraction to the GC was realised using a standard split injector to vaporise the compounds and LC eluent. Gas phase splitting was applied to match LC mass load and GC column loadability. The standard deviations of the peak areas obtained in this way were better than 7% (n = 6). The reliability of the system was demonstrated by the problem-free analysis of large series of oil and fat samples, with the focus on both intact triglycerides and their fatty acid methyl esters (FAMEs). Finally, the hyphenation of the automated LCxGC system to a sensitive and rapid-scanning time-of-flight mass spectrometer was realised. By using LCxGC-ToF MS, the information density of the chromatograms could be improved even further, which allowed easy identification of individual compounds as well as compound groups.
- On-line LC-GC and comprehensive two-dimensional LCxGC-ToF MS for the analysis of complex samples
Hans-Gerd Janssen, Sjaak de Koning, Udo A. Th. Brinkman. Anal Bioanal Chem (2004) 378 : 1944-1947
- New trend in sample preparation: on-line microextraction in packed syringe for liquid and gas chromatography applications
I. Determination of local anaesthetics in human plasma samples using gas chromatography-mass spectrometry
Mohamed Abdel-Rehim. Journal of Chromatography B, 801 (2004) 317-321<< Read Abstract >>A new technique for sample preparation on-line with LC and GC-MS assays was developed. Microextraction in a packed syringe (MEPS) is a new miniaturised, solid-phase extraction technique that can be connected on-line to GC or LC without any modifications. In MEPS approximately 1 mg of the solid packing material is inserted into a syringe (100-250 µl) as a plug. Sample preparation takes place on the packed bed. The bed can be coated to provide selective and suitable sampling conditions. The new method is very promising. It is very easy to use, fully automated, of low cost and rapid in comparison with previously used methods. This paper presents the development and validation of a method for microextraction in packed syringe MEPS on-line with GC-MS. Local anaesthetics in plasma samples were used as model substances. The method was validated and the standard curves were evaluated by the means of quadratic regression and weighted by inverse of the concentration: 1/x for the calibration range 5-2000 nM. The applied polymer could be used more than 100 times before the syringe was discarded. The extraction recovery was between 60 and 90%. The results showed close correlation coefficients (R>0.99) for all analytes in the calibration range studied. The accuracy of MEPS-GC-MS was between 99 and 115% and the inter-day precision (n=3 days), expressed as the relative standard deviation (R.S.D.%), was 3-10%.
- Evaluation of large volume-difficult matrix introduction-gas chromatography-time of flight-mass spectrometry (LV-DMI-GC-TOF-MS) for the
determination of pesticides in fruit-based baby foods
K. Patel, R. J. Fussell, D. M. Goodall and B. J. Keely, Food Additives and Contaminants, Vol. 21, No. 7 (July 2004), pp. 658-669<< Read Abstract >>The European Union Baby Food Directive (1999/39/EC), which came into force on 1 July 2002, set legal maximum residue levels at 0.01 mg kg-1 for all pesticides in baby foods. The combination of large volume-difficult matrix introduction (LV-DMI) with gas chromatography-time of flight-mass spectrometry (GC-TOF-MS), described herein, provides the analyst with a simple but rapid alternative GC-MS technique for the multiresidue analysis of pesticides in fruit-based baby foods. Samples were extracted with ethyl acetate in the presence of Na2SO4 and NaHCO3 and the crude extracts were analysed directly using LV-DMI-GC-TOF-MS. The best overall results (98 pesticides quantified satisfactorily at a spiking level of 0.01 mg kg-1) were obtained by analysis of concentrated extracts (2.5 g crop ml-1) using a 30-m column, with a chromatographic run time of 25 min. A good signal-to-noise ratio was obtained at the lowest calibrated level (0.0125 µg ml-1), with excellent linearity achieved over the range 0.0125-0.25 µg ml-1 (equivalent to 0.005-0.1 mg kg-1). Average recoveries for the analysis of five replicate determinations at a spiking level of 0.01 mg kg-1 were between 79 and 114% with relative standard derivations generally less than 20%.
- Miniaturised pressurised liquid extraction of chloroanilines from soil with subsequent analysis by large-volume injection-gas
E. Maria Kristenson, Silvia Angioi, Rene J.J. Vreuls, Maria Carla Gennaro, Udo A.Th. Brinkman. Journal of Chromatography A, 1058 (2004) 243-249<< Read Abstract >>A number of chloroanilines were extracted from soil by means of miniaturised pressurised liquid extraction (PLE). The extraction procedure was optimised for both large-volume on-column (LV-OC) and programmed-temperature vaporisation (PTV) injections combined with GC-MS. Hexane was the only extraction solvent suited for LV-OC and hexane/acetone gave the best results when using a PTV. Overall, the hexane/acetone-plus-PTV procedure shows better results than the hexane-plus-LV-OC method in terms of analyte recovery (36-109% versus 5-87%), repeatability (8-13% versus 4-31%) and detection limits. Both approaches allow detection of the chloroanilines in complex soil samples down to the 5-50 ng/g range. However, the PTV-based procedure is superior as regards robustness: over one hundred samples can be analysed without any maintenance being required.
- A streamlined approach to the analysis of volatile fatty acids and its application to the measurement of whole-body flux
Douglas J. Morrison, Karen Cooper, Susan Waldron, Christine Slater, Lawrence T. Weaver and Tom Preston Rapid Commun. Mass Spectrom. 2004; 18: 2593-2600<< Read Abstract >>Volatile fatty acids (VFAs) are produced in the human colon by the bacterial breakdown of carbohydrates that escape digestion and absorption in the small intestine. They have important local and systemic effects on gastrointestinal and nutritional functions. Measuring their production is difficult because of inaccessibility of sampling sites and low circulating concentrations. Stable isotope tracer techniques are a way to measure VFA production but require measurement of isotope dilution in blood and other biological fluids. We have developed a streamlined and robust method to measure the concentration and enrichment of [2H]-labelled VFAs by gas chromatography/mass spectrometry (GC/MS) and [13C]-labelled VFAs by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Both types of analysis were carried out on the same samples allowing multiple tracer studies to be conducted. Good accuracy and repeatability were found for GC/MS analysis of [2H]-labelled VFAs. Careful handling of the background contribution, especially acetate, allowed quantitation of concentration and enrichment within the analysis. GC/C/IRMS analysis of [13C] VFAs was also achieved with good accuracy and repeatability. This methodology was used to determine whole-body acetate production in two subjects using multiple tracers ([2H3]- and [1-13C]acetate) and blood and urine sampling.Whole-body acetate flux was similar when measured either with [2H3]- or [1-13C]acetate, and when flux was determined from plasma or urine tracer enrichment. This new method will permit rapid and accurate measurement of VFA flux using [2H]- and/or [13C]-labelled VFAs as tracers. Measurements of the contribution of colonic VFA production to whole-body VFA flux are now possible.
- Development of a Method for Dioxin Analysis of Small Serum Samples with Reduced Risk of Volatilization
Kimiyoshi Kitamura, Yoshikatsu Takazawa, Yoshiyuki Takei, Xiaojing Zhou, Shunji Hashimoto, Jae-Won Choi, Hiroyasu Ito, and Masatoshi Morita Anal. Chem. 2005, 77, 1727-1733<< Read Abstract >>To analyze the dioxin content of samples, including dibenzo-p-dioxins/dibenzofurans, and coplanar polychlorinated biphenyls (Co-PCBs), a large volume is usually necessary. This is difficult, however, when analyzing clinical samples, such as serum and tissue. We therefore sought to increase the sensitivity of high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS) in analyzing dioxins by injecting most of the extract from a small clinical sample. The concentration of each congener was estimated by injecting extracts of 5-g samples into a gas chromatography capillary precolumn (AT column) and by assaying extracts of 25-g samples by conventional splitless methods. We found that the limit of detection with the AT column was lower than that obtained by the splitless technique. In the AT column technique, 100 µL of the 110-µL final solution, equivalent to 4.5 g of the original sample, was injected into HRGC/HRMS. In contrast, 2 µL of the 20-µL final solution, equivalent to 2.5 g of original sample, was assayed using the splitless method. Moreover, when 25 fg of ultratrace dioxin was added to 100 µL of HRGC/HRMS sample and injected into the AT column, the peak area was almost the same as that obtained with 2 µL of HRGC/HRMS sample injected using the splitless method. Although assaying 10-20 µL of sample by the splitless method presents difficulties due to sample volatility, this problem can be reduced by using volumes larger than 100 µL. We tested this application by quantifying the parts-per-trillion levels, on a lipid weight basis, of each congener in a serum sample of 5 g using the AT column HRGC/HRMS method. We found this application to be successful and practical for mass screening of dioxin exposure in clinical samples.
- Use of automated direct sample introduction with analyte protectants in the GC-MS analysis of pesticide residues
Tomas Èajka, Kateøina Mastovska, Steven J. Lehotay, Jana Hajslova. J. Sep. Sci. 2005, 28, 1048-1060<< Read Abstract >>Automated large-volume direct sample introduction, or difficult matrix introduction (DMI), was investigated in the determination of 44 pesticide residues possessing a wide range of physico-chemical properties (volatility, polarity, pK(a)) in fruit-based baby food by means of gas chromatography-mass spectrometry (GC-MS) with a quadrupole mass analyzer. DMI has advantages over traditional injection because large volumes (up to 30 microL) of potentially dirty sample extracts can be injected into the GC-MS, but nonvolatile matrix components that would normally contaminate the inlet are removed after every injection. The extra matrix and glass surfaces involved in DMI, however, make the system more prone to the matrix-induced chromatographic enhancement effect, which adversely affects quantification of several pesticides. To overcome this problem, matrix-matched calibration standards and/or the use of analyte protectants were applied in the DMI approach, and the analysis of extracts was also compared before and after undergoing clean-up by dispersive solid-phase extraction. For best quantification, clean-up was still needed, and the combination of matrix-matching with analyte protectants gave the most reproducible results. Depending on the application, however, the addition of analyte protectants (a mixture of 3-ethoxy-1,2-propanediol, L-gulonic acid 3-lactone, and D-sorbitol) to sample extracts and calibration standards in solvent (non-matrix matched), gave satisfactory quantification for most of the 44 pesticides tested. The lowest calibration levels for 34 of the 44 pesticides were < or = 10 ng/g, which meets the standard required by the European Union Baby Food Directive (2003/13/EC).
- Application of direct thermal desorption gas chromatography and comprehensive twodimensional
gas chromatography coupled to time of flight mass spectrometry for analysis of organic compounds in ambient aerosol particles
Jurgen Schnelle-Kreis, Werner Welthagen, Martin Sklorz, Ralf Zimmermann. J. Sep. Sci. 2005, 28, 1648-1657<< Read Abstract >>Semivolatile organic compounds (SVOC) associated with ambient particles smaller than 2.5 m (PM2.5) were determined in the city of Augsburg, Germany. Daily samples were collected at a central monitoring station from late summer 2002 to spring 2005. SVOC were analysed by direct thermal desorption (DTD)-GC and comprehensive 2-D GC coupled to TOF MS (DTD-GC-TOF MS and DTD-GC-GC-TOF MS). Two hundred compounds were quantified and semi-quantified on a daily basis by DTD-GC-TOF MS. n-Alkanes, n-alkan-2-ones, n-alkanoic acid methyl esters, acetic acid esters, n-alkanoic acid amides, nitriles, linear alkylbenzenes and 2-alkyl-toluenes, hopanes, PAH, alkylated PAH and oxidised PAH, and several compounds that are not grouped in homologous rows or compound classes were determined. Changes in concentration and pattern of several target compounds as well as methodological advantages and restrictions of DTD-GC-TOF MS are briefly discussed. DTD-GC-TOF MS analysis provided data particularly suited for source receptor modelling and epidemiological time series studies on the health effects of ambient PM. GCxGC enhances chromatographic resolution of PM samples and therefore amplifies the peak identification capabilities of the TOF MS.
- Analysis of particle-associated semi-volatile aromatic and aliphatic hydrocarbons in urban particulate matter on a daily basis
Jurgen Schnelle-Kreis, Martin Sklorz, Anette Peters,Josef Cyrysb, Ralf Zimmermann. Atmospheric Environment 39 (2005) 7702-7714.<< Read Abstract >>PM2.5 Particle-associated semi-volatile organic compounds (SVOC) were determined in the city of Augsburg, Germany. Daily samples were collected at a central monitoring station from late summer to late autumn 2002. The concentrations of polycyclic aromatic hydrocarbons (PAH), oxidized PAH (O-PAH), n-alkanes, hopanes and long chain linear alkylbenzenes were determined by direct thermal desorption-gas chromatography-time of flight mass spectrometry (DTD-GC-TOFMS). Additionally, PM2.5 particle mass and number concentrations were measured. The sampling campaign can be divided into two parts, distinguished by a lower temperature level in the second part of the campaign. The particulate mass concentration showed no significant changes, whereas most of the SVOC had significant higher mean and peak concentrations in the colder period. The analysis of the data showed an increased influence of non-traffic sources in the colder period, reflected by a weak shift in the PAH profile and a significant shift in the hopane pattern. Statistical analysis of the inter-group correlations was carried out. Eight clusters partly representing different sources of the aerosol have been identified.
- Automated GC-MS analysis of raw biological samples. Application to fatty acid profiling of aquatic micro-organisms.
Akoto L., Pel R.,Brinkman U., Vreuls R.J.J. J. Anal. Appl. Pyrol., 73, (2005) 69-75<< Read Abstract >>A direct thermal desorption (DTD) interface was applied to profile the fatty acid composition of whole/intact aquatic micro-organisms using trimethylsulfonium hydroxide (TMSH) as derivatization reagent in a fully automated fashion without any sample treatment.
DTD was used to release cellular free and esterified fatty acids, after conversion into their methyl esters, from the very limited amounts of cells available in plankton community analysis using fluorescence-activated cell sorting of mixed (natural) microbial/algal populations. The liner of the GC injector is used as a sample-and-reaction container with the aid of the DTD interface. The fatty acids are converted into their methyl esters after an incubation (hydrolysis) time of 30 min with TMSH. After transportation into the injector, the liner is heated to effect thermally assisted methylation. Simultaneously, the fatty acid methyl esters (FAMEs) are introduced from the liner into the capillary GC column.
On the basis of peak intensities, the fatty acid compositions, thus obtained, were shown to be closely similar to those of a conventional lipid extraction and methylation procedure.
The method was applied to some common freshwater algae, the green algae Scenedesmus acutus, the diatom Asterionella formosa and the filamentous cyanobacterium, Limnothrix sp. strain MRI. Using this novel method, poly-unsaturated fatty acids were methylated into their corresponding methyl esters without isomerization/pyrolytic side-reactions.
The present method has been used to perform large series of analyses of algal and microbial cells. Up to 18 samples could be analysed per day. In order to reach this sample throughput, preparation of the (n + 1)th sample was performed simultaneously with GC analysis of the nth sample.
- Ultratraces analysis of organochlorine pesticides in drinking water by solid phase extraction coupled with large volume injection/gas chromatography/
Silvia H. G. Brondi Fernanda C. Spoljaric Fernando M. Lancas. J. Sep. Sci. 2005, 28, 2243-2246.<< Read Abstract >>This study describes an SPE coupled with large volume injection (LVI) analytical method for the analysis of organochlorine pesticides, BHC (α, β, δ), aldrin, endosulfan (α, β), endrin, dieldrin, and DDT, from aqueous samples. Determination was carried out by GC with MS. The LODs of organochlorine pesticides were determined at 10 ng/L concentration levels, and the results show that SPE-LVI-GC/MS has the potential to accurately determine organochlorine pesticides in water, as it avoids analyte classes in the various steps of a typical extraction procedure.
- Injectors for capillary gas chromatography and their application to environmental analysis
Renata Bailey J. Environ. Monit., 2005,7, 1054-1058<< Read Abstract >>The application of different injectors in capillary gas chromatography (GC) analysis of semi-volatile organic contaminants in environmental samples prepared in organic solvents is reviewed. The injectors examined include a split/splitless injector in splitless mode (SS), cold on-column (COC), and programmable temperature vaporizer (PTV) and adaptations of these injector designs. Key issues when selecting an injector include properties of the analyte, such as potential for thermal degradation or discrimination of high boiling point compounds within the injector, and the ability of the GC systems to handle large volume injections (LVI) primarily to lower detection limits and allow direct coupling with sample preparation techniques such as at-line or on-line solid phase extraction (SPE). LVI also require consideration of matrix interference issues. This review examines only injector chamber modifications that are feasible with a standard GC configuration, however some modifications to the chromatographic system to extend the range of applicability of gas chromatography analysis for environmental samples are also noted.
- Automated DMI for screening of cosmetic products
Erwin Kaal, Hans-Gerd Janssen, University ofAmsterdam and Mitsuhiro Kurano, ATAS GL International Shimadzu News, 1/2006 page 6-8.
- Organische Verbindungen in Feinstaub (German language)
Nachrichten aus der Chemie, 54, Juni 2006, 676
- Mass Spectrometry-Based Metabolic Profiling Reveals Different Metabolite Patterns in Invasive Ovarian Carcinomas and
Ovarian Borderline Tumors
Carsten Denkert, Jan Budczies, Tobias Kind, Wilko Weichert, Peter Tablack, Jalid Sehouli, Silvia Niesporek, Dominique Könsgen, Manfred Dietel, and Oliver Fiehn. Cancer Res 2006; 66: (22)10795-804. November 15, 2006<< Read Abstract >>Metabolites are the end products of cellular regulatory processes, and their levels can be regarded as the ultimate response of biological systems to genetic or environmental changes. We have used a metabolite profiling approach to test the hypothesis that quantitative signatures of primary metabolites can be used to characterize molecular changes in ovarian tumor tissues. Sixty-six invasive ovarian carcinomas and nine borderline tumors of the ovary were analyzed by gas chromatography/time-of-flight mass spectrometry (GCTOFMS) using a novel contamination-free injector system. After automated mass spectral deconvolution, 291 metabolites were detected, of which 114 (39.1%) were annotated as known compounds. By t test statistics with P < 0.01, 51 metabolites were significantly different between borderline tumors and carcinomas, with a false discovery rate of 7.8%, estimated with repeated permutation analysis. Principal component analysis (PCA) revealed four principal components that were significantly different between both groups, with the highest significance found for the second component (P = 0.00000009). PCA as well as additional supervised predictive models allowed a separation of 88% of the borderline tumors from the carcinomas. Our study shows for the first time that large-scale metabolic profiling using GC-TOF MS is suitable for analysis of fresh frozen human tumor samples, and that there is a consistent and significant change in primary metabolism of ovarian tumors, which can be detected using multivariate statistical approaches. We conclude that metabolomics is a promising high-throughput, automated approach in addition to functional genomics and proteomics for analyses of molecular changes in malignant tumors.
- Screening of tropical fruit volatile compounds using solid-phase microextraction (SPME) fibers and internally cooled SPME fiber
Carasek E, Pawliszyn J. J Agric Food Chem. 2006 Nov 15;54(23):8688-96.<< Read Abstract >>In this study, the optimization and comparison of an internally cooled fiber [cold fiber with polydimethylsiloxane (PDMS) loading] and several commercial solid-phase microextraction (SPME) fibers for the extraction of volatile compounds from tropical fruits were performed. Automated headspace solid-phase microextraction (HS-SPME) using commercial fibers and an internally cooled SPME fiber device coupled to gas chromatography-mass spectrometry (GC-MS) was used to identify the volatile compounds of five tropical fruits. Pulps of yellow passion fruit (Passiflora edulis), cashew (Anacardium occidentale), tamarind (Tamarindus indica L.), acerola (Malphigia glabra L.), and guava (Psidium guajava L.) were sampled. The extraction conditions were optimized using two experimental designs (full factorial design and Doehlert matrix) to analyze the main and secondary effects. The volatile compounds tentatively identified included alcohols, esters, carbonyl compounds, and terpernes. It was found that the cold fiber was the most appropriate fiber for the purpose of extracting volatile compounds from the five fruit pulps studied.
- Field Sampling with a Polydimethylsiloxane Thin-Film
Leslie Bragg, Zhipei Qin, Mehran Alaee, and Janusz Pawliszyn Journal of Chromatographic Science, Vol. 44, July 2006<< Read Abstract >>Abstract
In this research, field samplers are developed using polydimethylsiloxane (PDMS) thin-film as the extraction phase. This technique is based on a similar theory, the solid-phase microextraction (SPME) technique. More specifically, the development of the field sampler involves cutting a section of PDMS thin-film into a specific size and shape, and mounting it onto a stainless steel wire (the handle). The thin-film is then placed into a protective copper cage prior to deployment to prevent standards in the extraction phase is used to introduce an isotopically labeled internal standard for on-site calibration. The initial loading of the standard onto the thin-film and the amount of standard remaining on the thin-film are determined using gas chromatography-mass spectrometry and subsequently used to estimate the concentration of the target analytes. In addition, the field samplers are deployed in the field at two locations (the Meuse River in Eijsden, The Netherlands from April to May, 2005 and Hamilton Harbour located at the western tip of Lake Ontario, ON, Canada from September to December, 2006). Polycyclic aromatic hydrocarbons are identified, and concentrations of fluoranthene and pyrene are estimated in the low ng/L range. The results from both sampling sites are within the expected ranges for environmental samples. This polymeric extraction phase has a high surface-to-volume ratio compared with SPME, which results in higher sensitivity and mass uptake, leading to the detection of lower levels of analytes that many other techniques are unable to achieve.
- On-line size exclusion chromatography-pyrolysis-gas chromatography-mass spectrometry for copolymer characterization and additive analysis
Erwin R. Kaal, Geert Alkema, Mitsuhiro Kurano, Margit Geissler, Hans-Gerd Janssen. Journal of Chromatography A, 1143 (2007) 182-189.<< Read Abstract >>On-line coupled size exclusion chromatography-pyrolysis gas chromatography mass spectrometry (SEC-Py-GC-MS) is studied as a novel tool for the characterization of complex polymer samples. An automated system for on-line SEC-Py-GC-MS allowing transfer of multiple fractions was developed based on stop-flow operation of the SEC dimension, syringe-based transfer of the SEC fraction to the GC instrument and solvent elimination with subsequent pyrolysis in a programmed temperature vaporization (PTV) injector. After optimization the system was applied to the characterization of a complex terpolymer composed of very similar monomers. The use of the system for combined pyrolysis and additive analyses in polycarbonate was also demonstrated. Results obtained with the new method indicate the interesting potentials of the method for detailed characterization of polymeric materials.
- Evaluation of the QuEChERS sample preparation approach for the analysis of pesticide residues in olives
Sara C. Cunha, Steven J. Lehotay, Katerina Mastovska, Jos. O. Fernandes,Maria Beatriz, P. P. Oliveira. J. Sep. Sci. 2007, 30, 620 - 632.<< Read Abstract >>This paper describes the use of a quick, easy, cheap, effective, rugged, and safe (QuEChERS) method for extraction and cleanup of 16 pesticide residues of interest in olives and olive oil. These products contain a high lipid content, which can adversely affect pesticide recoveries and harm traditional chromatographic systems. For extraction, the main factors (oil and water content) were studied and optimized in experiments to maximize pesticide recoveries. Dispersive SPE with different sorbents was also investigated to minimize matrix coextractives and interferences. For analysis, a new automated DSI device was tested in GC-MS to avoid nonvolatile coextractives from contaminating the instrument. LC-MS/MS with positive ESI was used for those pesticides that were difficult to detect by GC-MS. The final method was validated for olives in terms of recoveries, repeatabilities, and reproducibilities using both detection techniques. The results demonstrated that the method achieved acceptable quantitative recoveries of 70-109% with RSDs <20% for DSI-GC-MS and 88-130% with RSDs <10% for LC-MS/MS, and LOQ at or below the regulatory maximum residue limits for the pesticides were achieved.
- On-line SEC-Py-GC-MS for the Automated Comprehensive Characterization of Copolymers (coupling matters)
Erwin R. Kaal, Mitsuhiro Kurano, Margit Geißer, Peter schoenmakers and Hans-Gerd Janssen. LC·GC Europe September 2007, 444-452 (coupling matters).<< Read Abstract >>Size-exclusion chromatography (SEC) and pyrolysis-gas chromatography (Py-GC) are commonly used to characterize copolymers. SEC is a powerful method to determine the molecular-weight distribution of polymers whereas Py-GC provides valuable information on their chemical composition. The combination of these two techniques could yield combined size and composition information for copolymers or polymer mixtures. A fully automated system was constructed to perform these two-dimensional (2D) characterizations. Several examples of the use of this new technique to comprehensively characterize polymers are described.
- Determination of the carbon isotopic composition of whole/intact biological specimens using at-line direct thermal desorption to effect thermally assisted hydrolysis/methylation.
Akoto L, Vreuls RJ, Irth H, et al. J Chromatogr A 2007 Sep 11.<< Read Abstract >>In this paper, we discuss the use of a direct thermal desorption (DTD) interface as an alternative to Curie-point flash pyrolysis system as an inlet technique in gas chromatography-combustion isotope-ratio mass spectrometry (GC/C-IRMS) analysis of whole/intact phytoplankton and zooplankton specimens. The DTD in combination with a combipal auto-injector is programmed to perform the injection, evaporation of solvents, transport of capped programmed-temperature vaporizer (PTV) liners to the PTV injector and chemical derivatisation (thermally assisted hydrolysis/methylation; THM) such that a profile of a cellular fatty acids is obtained. Flow-cytometric sorted microalgae and handpicked zooplankton are used as samples with trimethylsulfonium hydroxide (TMSH) as methylating reagent. A major advantage of this novel approach over the Curie-point technique is the automation of the total procedure, which allows unattended analysis of large sample series. The profiles and delta(13)C carbon isotopic signatures of the fatty acid methyl esters (FAMEs) produced are very similar to those obtained using the Curie-point flash pyrolysis method. It is shown that algal samples must be kept no longer than 48h in the DTD sample tray prior to the THM-analysis in order to maintain the integrity of their FAME profile.
- Fatty acid profiling of raw human plasma and whole blood using direct thermal desorption combined with gas chromatography-mass spectrometry.
Akoto L, Vreuls RJ, Irth H, et al. J Chromatogr A 2007 Sep 11.<< Read Abstract >>Gas chromatography (GC) has in recent times become an important tool for the fatty acid profiling of human blood and plasma. An at-line procedure used in the fatty acid profiling of whole/intact aquatic micro-organisms without any sample preparation was adapted for this work. A direct thermal desorption (DTD) interface was used to profile the fatty acid composition of human plasma and whole human blood of eight volunteers in a procedure omitting the usual lipid extraction steps that precede sample methylation in the traditional (off-line) protocols. Trimethylsulfonium hydroxide (TMSH) was used as reagent for thermally assisted methylation. In a fully automated manner, the liner of the GC injector is used as a sample-and-reaction container with the aid of the DTD interface. The fatty acid methyl ester (FAME) profiles obtained using this novel approach, were very identical to those obtained when the traditional off-line protocol was applied. FAME yields obtained in the at-line DTD method were found to be very similar for saturated fatty acids, but significantly higher for polyunsaturated fatty acids compared to off-line yields. As a result of the contribution of circulating cell membranes in blood, substantial differences were observed when the amount of FAMEs obtained in whole human blood and human plasma samples were compared after their analysis. Thanks to the fully automated operation of this novel procedure, large series of analyses can easily be performed.
- Characterization of olive oil volatiles by multi-step direct thermal desorption-comprehensive gas chromatography-time-of-flight mass
spectrometry using a programmed temperature vaporizing injector
Sjaak de Koning, Erwin Kaal, Hans-Gerd Janssen, Chris van Platerink, Udo A.Th. Brinkman article in press as: S. de Koning et al., Journal of Chromatography A, 1186 (2008) 228-235.<< Read Abstract >>The feasibility of a versatile system for multi-step direct thermal desorption (DTD) coupled to comprehensive gas chromatography (GC x GC)with time-of-flight mass spectrometric (TOF-MS) detection is studied. As an application the system is used for the characterization of fresh versus aged olive oil after treatment at 70, 175, 250 and 600°C.
- Evaluation of automated direct sample introduction with comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry
for the screening analysis of dioxins in fish oil
Eunha Hoh, Steven J. Lehotay, Katerina Mastovska, Janice K. Huwe Journal of Chromatography A, 1201 (2008) 69-77<< Read Abstract >>An automated direct sample introduction technique coupled to comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (DSI-GCxGC/TOF-MS) was applied for the development of a relatively fast and easy analytical screening method for 17 polychlorinated dibenzop-dioxins/dibenzofurans (PCDD/Fs) and 4 non-ortho polychlorinated biphenyls (PCBs) in fish oil. Comparison of instrumental performance between DSI-GCxGC/TOF-MS and the traditional gas chromatographic high resolution mass spectrometric (GC-HRMS) method showed good agreement of results for standard solutions analyzed in blind fashion. Relatively high tolerance of the DSI technique for lipids in the final extracts enabled a streamlined sample preparation procedure that only required gel permeation chromatography (GPC) and solid-phase extraction (SPE) cleanup with graphitized carbon black. The sample size for the method was 2 g of cod liver oil, which achieved limits of quantitation (LOQs)of 0.019-7.8 pg/g toxic equivalent quotients for the individual PCDD/Fs. Lower detection limits can be achieved by using larger sample size and scaling up the sample preparation procedure, but this adds to the labor, time, solvent consumption, and expense of the approach. However, the streamlined method yielded 0.94 pg/g and 2.3 pg/g LOQs for 2,3,7,8-tetrachloro dibenzofuran (TCDF) and 3,3.,4,4.,5-pentachloro biphenyl (CB126), whichwere sufficiently lowfor regulatory monitoring of 2 g samples. Therefore, instead of congener specific analysis, this streamlined analytical screening method for TCDF and CB126 has the potential to monitor fish oil contaminated with dioxin and dioxin-like PCBs at or above current food safety limits. Acceptable recoveries for nearly all analytes at three different spiking levels in fish oil sampleswere achieved with good repeatability.
- Hyphenation of aqueous liquid chromatography to pyrolysis-gas chromatography and mass spectrometry for the comprehensive
characterization of water-soluble polymers.
Erwin R. Kaal, Mitsuhiro Kurano, Margit Geißler, Hans-Gerd Janssen. Journal of Chromatography A, Volume 1186, Issues 1-2, 4 April 2008, Pages 222-227.<< Read Abstract >>A recently developed hyphenated system for organic size-exclusion chromatography-pyrolysis-gas chromatography-mass spectrometry (SEC-Py-GC-MS) is adapted to allow the use of aqueous LC eluents as applied in the characterization of water-soluble polymers. The system uses7 syringe-based transfer of multiple LC-fractions to the GC instrument with solvent elimination and subsequent pyrolysis in a programmed temperature vaporization injector. The problems of the large-volume injections of aqueous, salt containing eluents into the Py-GC-MS are solved by using a sintered-bed liner for elimination of the water at a high temperature, a volatile salt and the installation of a back-flush option. After optimization, the system was applied for the determination of the combined molecular weight-chemical composition of a polyethylene glycol-polypropylene glycol block copolymer. This analysis was done with the system in the aqueous SEC-Py-GC-MS mode. Also demonstrated is the automated at-line characterization of a random polystyrene-polymethylmethacrylate copolymer, now with the system in the gradient reversed-phase LC-Py-GC-MS mode. The methods proposed in the present work are very useful for the detailed characterization of water-soluble copolymers.
- Method Development and Application of Compound-Specific Isotope Analysis for Source Allocation of Polycyclic Aromatic
Hydrocarbons in Contaminated Soil.
MASTER THESIS of Flor Toledo Rodriguez, University Tübingen<< Read Abstract >>This investigation focuses on the application of compound-specific isotope analysis (CSIA) of carbon, a highly powerful and less known analytical technology, in order to assess the PAHs source allocation at a site with a massive and highly diverse contamination. With this method, the assessment of the carbon isotope ratios of PAHs can be used as source indicator at highly contaminated sites. The objective of this master thesis was to develop an extraction and purification method to isolate the PAHs from a complex contaminated soil matrix. Of special interest was to determine if the extraction and purification procedures affect the isotopic composition of the target analytes. This was of big importance since the main aim was the evaluation of the real isotopic composition of PAHs at the contaminated site. In order to achieve this objective, two enrichment and purification methods for the PAHs in the soil matrix were developed. The first method consisted of a liquid-solid extraction combined with a liquid-liquid extraction and a flash chromatography (LSE/LLE/FC), and the second method consisted of an accelerated solvent extraction combined with a liquid-liquid extraction and a final flash chromatography (ASE/LLE/FC). The comparison of the separated PAHs through these methods with respect to PAH standards showed that no detectable change in the isotopic composition of the target compounds occurred and therefore these purification methods can effectively be applied in highly PAH contaminated soil samples at the surveyed site through CSIA if soil samples contain a minimum concentration of PAHs of 11.1 mg/kg.
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- Rapid analysis of multiple pesticide residues in fruit-based baby food using programmed temperature vaporiser injection-low-pressure gas
chromatography-high-resolution time-of-flight mass spectrometry
Tomas Cajka, Jana Hajslova, Ondrej Lacina, Katerina Mastovska, Steven J. Lehotay Journal of Chromatography A, 1186 (2008) 281-294<< Read Abstract >>A rapid method using programmed temperature vaporiser injection-low-pressure gas chromatography-high-resolution time-of-flight mass spectrometry (PTV-LP-GC-HR-TOF-MS) for the analysis of multiple pesticide residues in fruit-based baby food was developed. The fast and inexpensive buffered QuEChERS (quick, easy, cheap, effective, rugged, and safe) extraction method and "conventional" approach that employs ethyl acetate extraction followed by gel permeation chromatography (GPC) cleanup were employed for sample preparation. A PTV injector in solvent venting mode was used to reduce volume of acetonitrile and acetic acid (from the buffered QuEChERS extracts) that caused higher column bleed without their elimination. Otherwise, the time-to-digital converter would become saturated in HR-TOF-MS. For fast GC separation allowing analysis of 100 analytes within a 7 min runtime, both a high temperature programming rate and vacuum conditions in a megabore GC column were employed. The use of HR-TOF-MS allowed the unbiased identification and reliable quantification of target analytes through the application of a narrow mass window (0.02 Da) for extracting analyte ions and the availability of full spectral information even at very low levels. With only a few exceptions, the lowest calibration levels for the pesticides tested were 0.01 mg/kg for both sample preparation methods, which meets the EU maximum residue limit set for pesticide residues in cereal-based foods and baby foods (2003/13/EC).
- Extending the molecular application range of gas chromatography
Erwin Kaal, Hans-Gerd Janssen Journal of Chromatography A, 1184 (2008) 43-60.<< Read Abstract >>Gas chromatography is an important analytical technique for qualitative and quantitative analysis in a wide range of application areas. It is fast, provides a high peak capacity, is sensitive and allows combination with a wide range of selective detection methods including mass spectrometry. However, the application area of GC is limited because the molecules to be analysed have to be thermally stable and sufficiently volatile. Numerous molecules do not meet these requirements and hence are not amenable to direct GC analysis. Recent research has resulted in better chromatographic columns and methods for sample preparation that enable a significant expansion of the molecular application range of GC. The strategies exploited include conversion of (macro)molecules into smaller species and approaches to reduce the polarity of molecules. In this review we identify four generic routes for extending the applicability of GC. These include high-temperature GC, derivatisation, pyrolysis and thermochemolysis. The principles, recent developments and future perspectives of these routes are discussed and examples of applications using the different options will be shown. Life sciences, metabonomics and profiling strategies for sample characterization are identified as important future drivers for the continued development of GC.
- Two-dimensional Characterization of (Bio-)macromolecules using LC-Py-GC-MS
Erwin R. Kaal, Hans-Gerd Janssen. GIT Spezial . Separation 1/2008. page 20-22.<< Read Abstract >>Unlike single compounds, polymers consist of many different molecules. These molecules are derived from the same building blocks, but diier in chain length, end-group, degree of branching, etc. For a true understanding of a polymer and its properties detailed knowledge of all features is necessary. Here it is generally not sufficient to just know the average distribution of isolated single parameters such as the molecular weight distribution or the average composition of the polymer. Multi-dimensional information is needed, giving for example copolymer composition as a function of molecular weight. Hyphenated combinations of a liquid chromatographic separation and pyrolysis GC provide an ideal means of deriving such information, as will be shown below.
- Fully automated system for the gas chromatographic characterization of polar biopolymers based on thermally assisted hydrolysis and methylation
Erwin Kaal, Sjaak de Koning, Stella Brudin, Hans-Gerd Janssen Journal of Chromatography A, 1201 (2008) 169-175.<< Read Abstract >>Pyrolysis-gas chromatography (Py-GC) is a powerful tool for the detailed compositional analysis of polymers. A major problem of Py-GC is that polar (bio)polymers yield polar pyrolyzates which are not easily accessible to further GC characterization. In the present work, a newly developed fully automated procedure for thermally assisted hydrolysis and methylation (THM) of biopolymers is described. Drying of the sample, addition of the reagent, incubation and pyrolysis are performed inside the liner of a programmable temperature vaporizer injector. The newsystemnot only allows efficient analysis of large series ofsamples, but also allows automated optimization of the experimental parameters based on an experimental design approach. The performance of the automated THM-procedurewas evaluated by performing THM-GC of a poly(acrylic acid)-poly(maleic anhydride) copolymer (PAA/PMAH) and several polysaccharides. The optimized THM-procedurewas applied for the structural characterization and differentiation of several lignins and hydroxypropylmethyl-celluloses. It was also applied to proteins. Here myoglobin and cytochrome c were used as the model compounds. Both conventional GC-mass spectrometry (MS) and comprehensive two-dimensional gas chromatography (GCxGC)-time-of-flight (TOF) MS were used for separation and identification of the species formed. The information obtained can aid in structure elucidation of polar biopolymers aswell as in providing detailed compositional information which can be used to differentiate structurally similar biopolymers.
- Comparison of Natural and Artificial Aging of Ballpoint Inks
Claudia Berger-Karin, Ursula Hendriks, Jochen Geyer-Lippmann. J Forensic Sci, July 2008, Vol. 53, No. 4.<< Read Abstract >>Solvent evaporation caused by aging from ballpoint inks was measured by gas chromatography . mass spectroscopy (GC .MS). The sample preparation was carried out with two different thermal desorption systems. The results are compared. Thirteen inks were classified with regard to their solvents, polymers, and additives. The variation of the aforementioned compounds caused by aging was monitored for naturally and artificially aged samples. In this paper, the results are compared and discussed with respect to forensic casework.
- A fast method for the identification of Mycobacterium tuberculosis in sputum and cultures based
on thermally assisted hydrolysis and methylation followed by gas chromatography-mass spectrometry
Erwin Kaal, Arend H.J. Kolk, Sjoukje Kuijper, Hans-Gerd Janssen. Journal of Chromatography A, 1216 (2009) 6319-6325<< Read Abstract >>A fast gas chromatography-mass spectrometry (GC-MS) method with minimum sample preparation is described for early diagnosis of tuberculosis (TB). The automated procedure is based on the injection of sputum samples which are thenmethylated inside the GC injector using thermally assisted hydrolysis and methylation (THM). The THM-GC-MS procedure was optimized for the injection of sputum samples. For the identification of Mycobacterium tuberculosis the knownmarker tuberculostearic acid (TBSA) and other potential markers were evaluated. Hexacosanoic acid in combination with TBSA was found to be specific for the presence of M. tuberculosis. For validation of the method several sputum samples with different viscosities spiked with bacterial cultures were analyzed. Finally, 18 stored sputum samples collected in Vietnam from patients suspected to suffer from TB were re-analyzed in Amsterdam by microscopy after decontamination/concentration and using the new THM-GC-MS method. No false positives were found by THM-GC-MS and all patients who were diagnosed with TB were also found positive using our newly developed THM-GC-MS method. These results show that the newfast and sensitive THM-GC-MS method holds great potential for the diagnosis of TB.
- Capabilities of Direct Sample Introduction-Comprehensive Two-Dimensional Gas Chromatography-Time-of-Flight Mass Spectrometry to Analyze
Organic Chemicals of Interest in Fish Oils
Eunha Hoh, Steven J. Lehotay, Katerina Mastovska, Helen L. NGO, Walter Vetter, Kristin C. Pangallo and Christopher M. Reddy Environ. Sci. Technol. 2009, 43, 3240-3247<< Read Abstract >>Most analytical methods for persistent organic pollutants (POPs) focus on individual groups of targeted analytes. Therefore, analysis of multiple classes of POPs typically entails several sample preparations, fractionations, and injections, whereas other chemicals of possible interest are neglected or lost. To analyze a wider scope of organic contaminants in fish oil, we developed an approach to combine the analysis of targeted and untargeted chemicals using an automated direct sample introduction (DSI) and comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GCxGC/ToF-MS). DSI-GCxGC/ToF-MS is a powerful tool that attains high quality separations to achieve high selectivity while still providing a wide analytical scope with minimal sample preparation, especially in conjunction with DSI’s high tolerance to dirty extracts. Gel permeation chromatography (GPC) was used for initial separation of lipids from POPs and other GC-amenable organic compounds from dietary cod liver oil. For comparison purposes, additional cleanup of the GPC extracts was done by silica adsorption and acidification, which helped provide clues in the identification of untargeted compounds, but in routine analysis, only GPC is needed for this analytical approach. The approach allowed simultaneous identification of known-POPs in the fish liver oils, and further permitted presumptive identifications of multiple groups of halogenated natural products (HNPs) and other organic chemicals of interest through comparisons of the mass spectra from analyses with those from mass spectral libraries and/or reports in the literature (60 PCB congeners and 76 compounds in total). Subsequent confirmations were made by reanalysis and comparison of chromatographic retention times and mass spectra with contemporaneously analyzed reference standards. Otherwise, ion fragmentation patterns of unknown compounds were assessed for tentative identifications. Some of the HNPs in the fish oils were detected and identified for the first time. Our study demonstrates that the wide monitoring scope provided by the DSI-GCxGC/ToF-MS method after GPC provides many logistical and performance advantages over the conventional use of several different methods designed for individual classes of targeted analytes after extensive sample preparation.
- Simultaneous Quantitation of Multiple Classes of Organohalogen Compounds in Fish Oils with Direct Sample Introduction Comprehensive
Two-Dimensional Gas Chromatography and Time-of-Flight Mass Spectrometry
Eunha Hoh, Steven J. Lehotay, Katerina Mastovska, Helen L. Ngo, Christopher M. Reddy, Kristin C. Pangallo and Walter Vetter J Agric Food Chem. 2009 Apr 8;57(7):2653-60<< Read Abstract >>We successfully optimized an analytical method using gel permeation chromatography followed by direct sample introduction comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry to quantify multiple groups of targeted persistent organic pollutants and halogenated natural products (HNPs) simultaneously in fish oil samples. This new method has a wider analytical scope than the traditional approach to use multiple methods to cover each class of compounds. Our analysis revealed that the relatively more volatile and lighter organic compounds, such as polychlorinated biphenyls (PCBs), organochlorine pesticides, and other smaller organohalogen compounds, were still present in two brands of “PCB-free” cod liver oils, albeit at much lower levels than in an untreated commercial sample. Moreover, the less volatile organic compounds, such as polybrominated diphenyl ethers and brominated HNPs, were detected at similar levels in all three cod liver oils. This suggests that the commercial molecular distillation treatment used for removal of organic/inorganic toxic contaminants is only effective for the lighter organic contaminants.
- Metabolic Profiling of Ultrasmall Sample Volumes with GC/MS: From Microliter to Nanoliter Samples
Maud M. Koek, Floor Bakels, Willem Engel, Arn van den Maagdenberg, Michel D. Ferrari, Leon Coulier and Thomas Hankemeier. Anal. Chem., 2010, 82 (1), pp 156-16<< Read Abstract >>Profiling of metabolites is increasingly used to study the functioning of biological systems. For some studies the volume of available samples is limited to only a few microliters or even less, for fluids such as cerebrospinal fluid (CSF) of small animals like mice or the analysis of individual oocytes. Here we present an analytical method using in-liner silylation coupled to gas chromatography/mass spectrometry (GC/MS), that is suitable for metabolic profiling in ultrasmall sample volumes of 2 µL down to 10 nL. Method performance was assessed in various biosamples. Derivatization efficiencies for sugars, organic acids, and amino acids were satisfactory (105-120%), and repeatabilities were generally better than 15%, except for amino acids that had repeatabilities up to about 35-40%. For endogenous sugars and organic acids in fetal bovine serum, the response was linear for aliquots from 10 nL up to at least 1 µL. The developed GC/MS method was applied for the analysis of different s ample matrixes, i.e., fetal bovine serum, mouse CSF, and aliquots of the intracellular content of Xenopus laevis oocytes. To the best of our knowledge, we present here the first comprehensive GC/MS metabolite profiles from mouse CSF and from the intracellular content of a single X. laevis oocyte.
- Comprehensive gas chromatography with Time of Flight MS and large volume
introduction for the detection of fluoride-induced regenerated nerve agent in biological samples
J.A. van der Meer, H.C. Trap, D. Noort, M.J. van der Schans. in press: J. Chromatogr. B (2010), doi:10.1016/j.jchromb.2010.02.019<< Read Abstract >>Recently, several methods have been developed to verify exposure to nerve agents. Most of these methods, such as the fluoride reactivation technique and the analysis of inhibited phosphonylated butyrylcholinesterase (BuChE), are based on mass spectrometry. The high specificity of the mass spectrometer might also imply a disadvantage, because the acquisition mass, i.e. the identity of the analyte must be known beforehand in order to direct the MS analysis in the most sensitive mode. In real cases, the identity of the nerve agent is not always known beforehand and the mass spectrometer should be operated in a scanning mode, with the consequence that sensitivity of the method will be lower. Comprehensive GC, or GCxGC, is a technique which offers enhanced separation. The implied larger selectivity of the GC separation allows mass spectrometry to be conducted in a less specific, scanning, mode. By the use of this configuration, the identity of the nerve agent does not have to be known beforehand but can be traced. In order to be able to detect lower concentrations and assess lower exposure levels, a large volume injection technique was developed allowing sample sizes up to 100µL. The technique was tested with plasma samples that had been inhibited with various nerve agents. Subsequently, the cholinesterasebound nerve agent was regenerated by the fluoride reactivation technique. Using the newly developed comprehensive GC-MS method it was possible to detect nerve agent at an exposure level of 1% BuChE inhibition, which is approximately 70 pg nerve agent/mL. These low exposure levels cannot be verified with a cholinesterase (ChE) activity assay. Moreover, the identity of the regenerated nerve agent was verified by the mass spectrum that was generated by the TOF mass spectrometer. This paper presents a technique able to deliver full-scan data on the analysis of nerve agents in biomedical samples at relevant exposure levels (1% BuChE inhibition). This full-scan data meets for a large part the forensic requirements that are in place for the analysis of biomedical samples in the context of alleged use of Chemical Warfare Agents.
- High Throughput Analysis of 150 Pesticides in Fruits and Vegetables using QuEChERS
and Low-Pressure Gas Chromatography-Time-of-Flight Mass Spectrometry
Urairat Koesukwiwat Steven J. Lehotay, Shui Miao and Natchanun Leepipatpiboon. in press: J. Chromatogr. A (2010.05.012)<< Read Abstract >>A higher monitoring rate is highly desirable in the labs, but this goal is typically limited by sample throughput. In this study, we sought to assess the real-world applicability of fast, low-pressure GC - time-of-flight MS (LP-GC/TOFMS) for the identification and quantification of 150 pesticides in tomato, strawberry, potato, orange, and lettuce samples. Buffered and unbuffered versions of QuEChERS (which stands for quick, easy, cheap, effective, rugged, and safe) using dispersive solid-phase extraction (d-SPE) and disposable pipette extraction (DPX) for cleanup were compared for sample preparation. For clean-up of all sample types, a combination of 150 mg MgSO4, 50 mg primary secondary amine (PSA), 50 mg C18, and 7.5 mg graphitized carbon black (GCB) per mL extract was used. No significant differences were observed in the results between the different sample preparation versions. QuEChERS took <10 min per individual sample, or <1 hr for 2 chemists to prepare 32 pre-homogenized samples, and using LP-GC/TOFMS, <10 min run time and <15 min cycle time allowed >32 injections in 8 hrs. Overall, >126 analytes gave recoveries (3 spiking levels) in the range of 70-120% with <20% RSD. The results indicate that LP-GC/TOFMS for GC-amenable analytes matches UHPLC-MS/MS in terms of sample throughput and turnaround time for their routine, concurrent use in the analysis of a wide range of analytes in QuEChERS extracts to achieve reliable quantification and identification of pesticide residues in foods.
- Large-volume Injection Coupled to Comprehensive Gas Chromatography- Time-of-Flight Mass Spectrometry for the Analysis of 3-MCPD Esters in Edible Oils
By Sjaak de Koning, Zuzana Zelinkova, Karel Hrncirik, and Hans-Gerd Janssen. March 19, 2010 Vol. 6, Number 5 issue of The Column, Pages 17-22<< Read Abstract >>
- Evaluation of comprehensive on-line liquid chromatography thermally assisted hydrolysis
and methylation-gas chromatography-mass spectrometry for characterization of sulfonated lignins.
Brudin S, Kaal E, Janssen HG, Schoenmakers P. J Sep Sci. 2010 Nov;33(22):3604-11.<< Read Abstract >>Sulfonated lignins, used as dispersants in agrochemical formulations, have been characterized by hyphenation of ion-pair RPLC and thermally assisted hydrolysis and methylation-GC-MC (THM-GC-MS). The chemical structure of a series of selected lignins was evaluated, both in terms of overall composition and in terms of composition as a function of molecular size. Some sulfonated lignins give rise to unstable formulations. In the compositional analysis, these samples were found to yield additional fragments. A newly developed comprehensive method made it possible to monitor the occurrence of these fragments as a function of molecular size. In addition to differences in the molecular size between "good" and "bad" batches, clear differences in chemical composition were established.
- Parasitoids select plants more heavily infested with their caterpillar hosts: a new approach to aid interpretation of plant headspace volatiles
Robbie D. Girling, Alex Stewart-Jones, Julie Dherbecourt, Joanna T. Staley, Denis J. Wright and Guy M. Poppy Proc. R. Soc. B doi:10.1098/rspb.2010.2725<< Read Abstract >>Plants produce volatile organic compounds (VOCs) in response to herbivore attack, and these VOCs can be used by parasitoids of the herbivore as host location cues. We investigated the behavioural responses of the parasitoid Cotesia vestalis to VOCs from a plant-herbivore complex consisting of cabbage plants (Brassica oleracea) and the parasitoids host caterpillar, Plutella xylostella. A Y-tube olfactometer was used to compare the parasitoids’ responses to VOCs produced as a result of different levels of attack by the caterpillar and equivalent levels of mechanical damage. Headspace VOC production by these plant treatments was examined using gas chromatography-mass spectrometry. Cotesia vestalis were able to exploit quantitative and qualitative differences in volatile emissions, from the plant-herbivore complex, produced as a result of different numbers of herbivores feeding. Cotesia vestalis showed a preference for plants with more herbivores and herbivore damage, but did not distinguish between different levels of mechanical damage. Volatile profiles of plants with different levels of herbivores/herbivore damage could also be separated by canonical discriminant analyses. Analyses revealed a number of compounds whose emission increased significantly with herbivore load, and these VOCs may be particularly good indicators of herbivore number, as the parasitoid processes cues from its external environment.
- Extension of the QuEChERS Method for Pesticide Residues in Cereals to Flaxseeds, Peanuts, and Doughs
Urairat Koesukwiwat, Steven J. Lehotay, Katerina Mastovska, Kelly J. Dorweiler, and Natchanun Leepipatpiboon J. Agric. Food Chem. 2010, 58, 5950-5958<< Read Abstract >>A simple method was evaluated for the determination of pesticide residues in flaxseeds, doughs, and peanuts using gas chromatography-time-of-flight mass spectrometry (GC-TOF) for analysis. A modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method, which was previously optimized for cereal grain samples, was evaluated in these fatty matrices. This extraction method involves first mixing the sample with 1:1 water/acetonitrile for an hour to swell the matrix and permit the salt-out liquid-liquid partitioning step using anhydrous MgSO4 and NaCl. After shaking and centrifugation, cleanup is done by dispersive solid-phase extraction (d-SPE) using 150 mg of anhydrous MgSO4, 150 mg of PSA, and 50 mg of C-18 per milliliter of extract. This method gave efficient separation of pesticides from fat and removal of coextracted substances better than gel permeation chromatography or use of a freeze-out step, which involved excessive use of solvent and/or time. The optimized analytical conditions were evaluated in terms of recoveries, reproducibilities, limits of detection, and matrix effects for 34 representative pesticides using different types of flaxseeds, peanuts, and doughs. Use of matrix-matched standards provided acceptable results for most pesticides with overall average recoveries between 70 and 120% and consistent RSDs <20% for semipolar pesticides and <26% for lipophilic pesticides. The recoveries of these latter types of pesticides depended on the fat content in the matrices and partitioning factor between the lipids and acetonitrile. We believe that the consistency of the pesticide recoveries for different samples in multiple experiments and the physicochemical partitioning explanation for <70% recoveries of lipophilic pesticides justify compensation of results for the empirically determined recovery values. In any case, this method still meets 10 ng/g detection limit needs for lipophilic pesticides and may be used for qualitative screening applications, in which any identified pesticides can be quantified and confirmed by a more intensive method that achieves >70% recoveries for lipophilic pesticides.
- Methyl salicylate production in tomato affects biotic interactions
Kai Ament, Vladimir Krasikov, Silke Allmann, Martijn Rep, Frank L.W. Takken and Robert C. Schuurink The Plant Journal (2010) 62, 124-134<< Read Abstract >>The role of methyl salicylate (MeSA) production was studied in indirect and direct defence responses of tomato (Solanum lycopersicum) to the spider mite Tetranychus urticae and the root-invading fungus Fusarium oxysporum f. sp. lycopersici, respectively. To this end, we silenced the tomato gene encoding salicylic acid methyl transferase (SAMT). Silencing of SAMT led to a major reduction in SAMT expression and MeSA emission upon herbivory by spider mites, without affecting the induced emission of other volatiles (terpenoids). The predatory mite Phytoseiulus persimilis, which preys on T. urticae, could not discriminate between infested and non-infested SAMT-silenced lines, as it could for wild-type tomato plants. Moreover, when given the choice between infested SAMT-silenced and infested wild-type plants, they preferred the latter. These findings are supportive of a major role for MeSA in this indirect defence response of tomato. SAMT-silenced tomato plants were less susceptible to a virulent strain of F. oxysporum f. sp. lycopersici, indicating that the direct defense responses in the roots are also affected in these plants. Our studies show that the conversion of SA to MeSA can affect both direct and indirect plant defence responses.
Keywords: methyl salicylate, Fusarium, tomato, spider mite, predatory mite.
- Comparison of QuEChERS sample preparation methods for the analysis of pesticide residues in fruits and vegetables.
Steven J. Lehotay, Kyung Ae Son, Hyeyoung Kwon, Urairat Koesukwiwat, Wusheng Fu, Katerina Mastovska, Eunha Hoh, Natchanun Leepipatpiboon Journal of Chromatography A, 1217 (2010) 2548-2560<< Read Abstract >>This article describes the comparison of different versions of an easy, rapid and low-cost sample preparation approach for the determination of pesticide residues in fruits and vegetables by concurrent use of gas and liquid chromatography (GC and LC) coupled to mass spectrometry (MS) for detection. The sample preparation approach is known as QuEChERS, which stands for “quick, easy, cheap, effective, rugged and safe”. The three compared versions were based on the original unbuffered method, which was first published in 2003, and two interlaboratory validated versions: AOAC Official Method 2007.01, which uses acetate buffering, and European Committee for Standardization (CEN) Standard Method EN 15662, which calls for citrate buffering. LC-MS/MS and GC-MS analyses using each method were tested from 50 to 1000 ng/g in apple-blueberry sauce, peas and limes spiked with 32 representative pesticides. As expected, the results were excellent (overall average of 98% recoveries with 10% RSD) using all 3 versions, except the unbuffered method gave somewhat lower recoveries for the few pH-dependent pesticides. The different methods worked equally well for all matrices tested with equivalent amounts of matrix co-extractives measured, matrix effects on quantification and chemical noise from matrix in the chromatographic backgrounds. The acetate-buffered version gave higher and more consistent recoveries for pymetrozine than the other versions in all 3 matrices and for thiabendazole in limes. None of the versions consistently worked well for chlorothalonil, folpet or tolylfluanid in peas, but the acetatebuffered method gave better results for screening of those pesticides. Also, due to the recent shortage in acetonitrile (MeCN), ethyl acetate (EtOAc) was evaluated as a substitute solvent in the acetate-buffered QuEChERS version, but it generally led to less clean extracts and lower recoveries of pymetrozine, thiabendazole, acephate, methamidophos, omethoate and dimethoate. In summary, the acetate-buffered version of QuEChERS using MeCN exhibited advantages compared to the other tested methods in the study.
- Pesticide multiresidue analysis in cereal grains using modified QuEChERS method combined with automated direct sample introduction GC-TOFMS and UPLC-MS/MS techniques.
Mastovska K, Dorweiler KJ, Lehotay SJ, Wegscheid JS, Szpylka KA. J Agric Food Chem. 2010 May 26;58(10):5959-72<< Read Abstract >>The QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation method was modified to accommodate various cereal grain matrices (corn, oat, rice, and wheat) and provide good analytical results (recoveries in the range of 70-120% and RSDs <20%) for the majority of the target pesticides (about 180 analytes). The method consists of a 1 h shaking of a milled sample (2.5-5 g) in 20 mL of 1:1 (v/v) water/acetonitrile (or 25 mL of 1.5:1 water/acetonitrile in the case of rice) to provide simultaneous matrix swelling and analyte extraction. Then, a MgSO(4)/NaCl salt mixture (4:1, w/w) is added to the extract to induce phase separation and force the pesticides into the upper acetonitrile layer, a 1 mL aliquot of which is subsequently cleaned up using dispersive solid phase extraction with 150 mg of PSA, 50 mg of C(18), and 150 mg of MgSO(4). GC-amenable pesticides were analyzed using gas chromatography combined with time-of-flight mass spectrometry (GC-TOFMS) and the automated direct sample introduction technique for a large volume injection of the extracts. Ultraperformance liquid chromatography coupled to triple-quadrupole tandem mass spectrometry (UPLC-MS/MS) was employed for the analysis of LC-amenable pesticides. This method was implemented in a routine laboratory, providing about 3-fold increased sample throughput, 40-50% reduction in the cost of disposable materials and in the operation costs, 1:100 solvent waste reduction, and increased scope of the analysis versus the traditional approach based on the Luke method.
- Determination of cholesterol and triglycerides in serum lipoproteins using flow
field-flow fractionation coupled to gas chromatography-mass spectrometry
Rashid Nazir Qureshi, Erwin Kaal, Hans-Gerd Janssen, Peter J. Schoenmakers, Wim Th. Kok Analytica Chimica Acta 2011.04.057<< Read Abstract >>Asymmetric flow field flow fractionation (AsFlFFF) was combined with pyrolysis-gas chromatography mass spectrometry for a sized based fractionation and a detailed compositional study of the triglycerides and cholesterol associated with the various lipoprotein subclasses present in human serum. Serum samples were injected in the AsFlFFF instrument and fractionated with a time-delayed exponential decay cross flow program. The fractions collected after AsFlFFF elution were injected into a programmable temperature vaporizer (PTV) GC-injector, containing a fritted liner. A temperature and split-flow program for the PTV injector was optimized for the thermally assisted hydrolysis and methylation of the compounds of interest. The resulting fatty acid and cholesterol methyl esters were separated by GC and characteristic fragment ions were detected by MS. The system was optimized and calibrated with triglyceride and cholesterol standards for quantitative analysis. The possible interference by phospholipids with the quantitative results was investigated and found to be of minor importance. The concentrations and lipoprotein profiles of triglycerides and cholesterol were determined in a pooled serum sample of healthy volunteers and a serum sample of a sepsis patient. The results obtained with the GC-MS approach were compared with those of a previously developed method based on AsFLFFF with a dual enzymatic reaction detection system. A good agreement of the profiles was found, for cholesterol as well as for the triglycerides, even when the GC-MS method quantifies the fatty acids while with the enzymatic reaction method the glycerol concentrations are determined. Total cholesterol and triglyceride concentration values for the serum samples showed good agreement with the results of the standard enzymatic method as used in practice in the university hospital.
> Lipoproteins from human serum were separated by size (HDL, LDL, VLDL) using field flow fractionation.
> Pyrolysis-GC-MS could be used to quantify cholesterol and triglycerides in the lipoprotein fractions.
> Cholesterol and triglyceride profiles measured in different samples were very similar to results obtained with other methods.
> Possibilities for fatty acid speciation and study of the cholesterol metabolism were shown.
Keywords: Lipoproteins; Cholesterol; Triglycerides; Asymmetric field flow fractionation; Pyrolysis-gas chromatography-mass spectrometry; Fatty acid profilin
- Pyrolysis-gas chromatography-mass spectrometry for studying N-vinyl-2-pyrrolidone-co-vinyl acetate copolymers and their dissolution behaviour
Aleksandra Chojnacka, Abdul Ghaffar, Andrew Feilden, Kevin Treacher, Hans-Gerd Janssen, Peter Schoenmakers Anal Chim Acta; 2011 Nov 14;706(2):305-11<< Read Abstract >>Knowledge on the solubility behaviour and dissolution rate of speciality and commodity polymers is very important for the use of such materials in high-tech applications. We have developed methods for the quantification and characterization of dissolved copolymers of N-vinyl-2-pyrrolidone (VP) and vinyl acetate (VA) during dissolution in water. The methods are based on pyrolysis (Py) performed in a programmed-temperature vaporization injector with subsequent identification and quantification of the components in the pyrolysate using capillary gas chromatography-mass spectrometry (GC-MS). By injecting large volumes and applying cryo-focussing at the top of the column, low detection limits could be achieved.
The monomer ratio was found to have the greatest effect on the dissolution rate of the PVP-co-VA copolymers. The material with the highest amount of VA (50%) dissolves significantly slower than the other grades. Size-exclusion chromatography (SEC) and Py-GC-MS were used to measure molecular weights and average chemical compositions, respectively. Combined off-line SEC//Py-GC-MS was used to determine the copolymer composition (VP/VA ratio), as a function of the molecular weight for the pure polymers. In the dissolution experiments, a constant VP/VA ratio across the dissolution curve was observed for all copolymers analysed. This suggests a random distribution of the two monomers over the molecules.
Keywords: Copolymer dissolution; Copolymer characterization; Pyrolysis-GC-MS; SEC; N-vinyl-2-pyrrolidone; Vinyl acetate
- An automated method for the analysis of phenolic acids in plasma based on ion-pairing micro-extraction coupled on-line to gas chromatography/mass spectrometry with in-liner derivatisation
Sonja Peters, Erwin Kaal, Iwan Horsting, Hans-Gerd Janssen doi:10.1016/j.chroma.2011.10.055<< Read Abstract >>A new method is presented for the analysis of phenolic acids in plasma based on ion-pairing Micro-extraction in packed sorbent (MEPS) coupled on-line to in-liner derivatisation-gas chromatography-mass spectrometry (GC-MS). The ion-pairing reagent served a dual purpose. It was used both to improve extraction yields of the more polar analytes and as the methyl donor in the automated in-liner derivatisation method. In this way, a fully-automated procedure for the extraction, derivatisation and injection of a wide range of phenolic acids in plasma samples has been obtained.
An extensive optimisation of the extraction and derivatisation procedure has been performed. The entire method showed excellent repeatabilities of under 10% and linearities of 0.99 or better for all phenolic acids. The limits of detection of the optimised method for the majority of phenolic acids were 10 ng/mL or lower with three phenolic acids having less-favourable detection limits of around 100 ng/mL. Finally, the newly-developed method has been applied in a human intervention trial in which the bioavailability of polyphenols from wine and tea was studied. Forty plasma samples could be analysed within 24 h in a fully-automated method including sample extraction, derivatisation and gas chromatographic analysis.
Keywords: automation; gas chromatography; micro-extraction in a packed sorbent (MEPS); ion-pairing extraction; in-liner derivatisation; plasma; phenolic acids
- In-situ derivatization thermal desorption GC-TOFMS for direct analysis of particle-bound non-polar and polar organic species
J. Orasche, J. Schnelle-Kreis, G. Abbaszade, and R. Zimmermann Atmos. Chem. Phys., 11, 8977-8993, 2011<< Read Abstract >>An in-situ derivatization thermal desorption method followed by gas chromatography and time-of-flight mass spectrometry (IDTD-GC-TOFMS) was developed for determination of polar organic compounds together with non-polar compounds in one measurement. Hydroxyl and carboxyl groups of compounds such as anhydrous sugars, alcohols and phenols, fatty acids and resin acids are targets of the derivatization procedure. Derivatization is based on silylation with N-Methyl-N-trimethylsilyltrifluoroacetamide (MSTFA) during the step of thermal desorption. The high temperature of 300°C during desorption is utilized for the in-situ derivatization on the collection substrate (quartz fibre filters) accelerating the reaction rate. Thereby, the analysis time is as short as without derivatization. At first the filter surface is dampened with derivatization reagent before insertion of the sample into the thermal desorption unit. To ensure ongoing derivatization during thermal desorption the carrier gas is enriched with MSTFA until the desorption procedure is finished. The precisions of all studied analytes were below 17% within a calibration range from 22 pg (abietic acid) up to 342 ng (levoglucosan). Limits of quantification (LOQ) for polycyclic aromatic hydrocarbons (PAH) were between 1 pg (fluoranthene) and 8 pg (indeno[1,2,3-cd]pyrene), for resin acids 37-102 pg and for studied phenols 4-144 pg. LOQ for levoglucosan was 17 pg.
- RNA-seq discovery, functional characterization, and comparison of sesquiterpene synthases from Solanum lycopersicum
and Solanum habrochaites trichomes
Petra M. Bleeker, Eleni A. Spyropoulou, Paul J. Diergaarde, Hanne Volpin, Michiel T. J. De Both, Philipp Zerbe, Joerg Bohlmann, Vasiliki Falara Yuki Matsuba, Eran Pichersky, Michel A. Haring, Robert C. Schuurink Plant Mol Biol (2011) 77:323-336<< Read Abstract >>Solanum lycopersicum and Solanum habrochaites (f. typicum) accession PI127826 emit a variety of sesquiterpenes. To identify terpene synthases involved in the production of these volatile sesquiterpenes, we used massive parallel pyrosequencing (RNA-seq) to obtain the transcriptome of the stem trichomes from these plants. This approach resulted initially in the discovery of six sesquiterpene synthase cDNAs from S. lycopersicum and five from S. habrochaites. Searches of other databases and the S. lycopersicum genome resulted in the discovery of two additional sesquiterpene synthases expressed in trichomes. The sesquiterpene synthases from S. lycopersicum and S. habrochaites have high levels of protein identity. Several of them appeared to encode for non-functional proteins. Functional recombinant p roteins produced germacrenes, ß-caryophyllene/a-humulene, viridiflorene and valencene from (E,E)-farnesyl diphosphate. However, the activities of these enzymes do not completely explain the differences in sesquiterpene production between the two tomato plants. RT-qPCR confirmed high levels of expression of most of the S. lycopersicum sesquiterpene synthases in stem trichomes. In addition, one sesquiterpene synthase was induced by jasmonic acid, while another appeared to be slightly repressed by the treatment. Our data provide a foundation to study the evolution of terpene synthases in cultivated and wild tomato.
- Novel approaches in diagnosing tuberculosis
Arend H. J. Kolk, Ngoc A. Dang, Sjoukje Kuijper, Tim Gibson, Richard Anthony, Mareli M. Claassens, Erwin Kaal, Hans-Gerd Janssen 05/2011; DOI:10.1117/12.883848<< Read Abstract >>ABSTRACT
The WHO declared tuberculosis (TB) a global emergency. An estimated 8-9 million new cases occur each year with 2-3 million deaths. Currently, TB is diagnosed mostly by chest-X ray and staining of the mycobacteria in sputum with a detection limit of 1x104 bacteria /ml. There is an urgent need for better diagnostic tools for TB especially for developing countries. We have validated the electronic nose from TD Technology for the detection of Mycobacterium tuberculosis by headspace analysis of 284 sputum samples from TB patients. We used linear discriminant function analysis resulting in a sensitivity of 75% a specificity of 67% and an accuracy of 69%. Further research is still required to improve the results by choosing more selective sensors and sampling techniques. We used a fast gas chromatography- mass spectrometry method (GC-MS). The automated procedure is based on the injection of sputum samples which are methylated inside the GC injector using thermally assisted hydrolysis and methylation (THM-GC-MS). Hexacosanoic acid in combination with tuberculostearic acid was found to be specific for the presence of M. tuberculosis. The detection limit was similar to microscopy. We found no false positives, all microscopy and culture positive samples were also found positive with the THM-GC-MS method. The detection of ribosomal RNA from the infecting organism offers great potential since rRNA molecules outnumber chromosomal DNA by a factor 1000. It thus may possible to detect the organism without amplification of the nucleic acids (NA). We used a capture and a tagged detector probe for the direct detection of M. tuberculosis in sputum. So far the detection limit is 1x106 bacteria / ml. Currently we are testing a Lab-On-A-Chip Interferometer detection system.
- Quality Evaluation of Olive Oil by Statistical Analysis of
Multicomponent Stable Isotope Dilution Assay Data of Aroma Active Compounds
Georg Dierkes, Annette Bongartz, Helmut Guth and Heiko Hayen. J. Agric. Food Chem., 2012, 60 (1), pp 394-401<< Read Abstract >>An instrumental method for the evaluation of olive oil quality was developed. Twenty-one relevant aroma active compounds were quantified in 95 olive oil samples of different quality by headspace solid phase microextraction (HS-SPME) and dynamic headspace coupled to GC-MS. On the basis of these stable isotope dilution assay results, statistical evaluation by partial least-squares discriminant analysis (PLS-DA) was performed. Important variables were the odor activity values of ethyl isobutanoate, ethyl 2-methylbutanoate, 3-methylbutanol, butyric acid, E,E-2,4-decadienal, hexanoic acid, guaiacol, 2-phenylethanol, and the sum of the odor activity values of Z-3-hexenal, E-2-hexenal, Z-3-hexenyl acetate, and Z-3-hexenol. Classification performed with these variables predicted 88% of the olive oils quality correctly. Additionally, the aroma compounds, which are characteristic for some off-flavors, were dissolved in refined plant oil. Sensory evaluation of these models demonstrated that the off-flavors rancid, fusty, and vinegary could be successfully simulated by a limited number of odorants.
Keywords:methyl salicylate, Fusarium, tomato, spider mite, predatory mite.
- Detection of Mycobacterium tuberculosis in Sputum by Gas Chromatography-Mass Spectrometry of Methyl Mycocerosates Released by Thermochemolysis
Denise M. O'Sullivan, Simona C. Nicoara, Reggie Mutetwa, Stanley Mungofa, Oona Y-C. Lee, David E. Minnikin, Max W. Bardwell, Elizabeth L. Corbett, Ruth McNerney and Geraint H. Morgan PLoS One. 2012; 7(3): e32836.<< Read Abstract >>Tuberculosis requires rapid diagnosis to prevent further transmission and allow prompt administration of treatment. Current methods for diagnosing pulmonary tuberculosis lack sensitivity are expensive or are extremely slow. The identification of lipids using gas chromatography- electron impact mass spectrometry (GC-EI/MS) could provide an alternative solution. We have studied mycocerosic acid components of the phthiocerol dimycocerosate (PDIM) family of lipids using thermochemolysis GC-EI/MS. To facilitate use of the technology in a routine diagnostic laboratory a simple extraction procedure was employed where PDIMs were extracted from sputum using petroleum ether, a solvent of low polarity. We also investigated a method using methanolic tetramethylammonium hydroxide, which facilitates direct transesterification of acidic components to methyl esters in the inlet of the GC-MS system. This eliminates conventional chemical manipulations allowing rapid and convenient analysis of samples. When applied to an initial set of 40 sputum samples, interpretable results were obtained for 35 samples with a sensitivity relative to culture of 94% (95%CI: 69.2,100) and a specificity of 100% (95%CI: 78.1,100). However, blinded testing of a larger set of 395 sputum samples found the assay to have a sensitivity of 61.3% (95%CI: 54.9,67.3) and a specificity of 70.6% (95%CI: 62.3,77.8) when compared to culture. Using the results obtained we developed an improved set of classification criteria, which when applied in a blinded re-analysis increased the sensitivity and specificity of the assay to 64.9% (95%CI: 58.6,70.8) and 76.2% (95%CI: 68.2,82.8) respectively. Highly variable levels of background signal were observed from individual sputum samples that inhibited interpretation of the data. The diagnostic potential of using thermochemolytic GC-EI/MS of PDIM biomarkers for diagnosis of tuberculosis in sputum has been established; however, further refinements in sample processing are required to enhance the sensitivity and robustness of the test.
- Rapid Multidimensional Liquid-Gas Chromatography for the Analysis of Saturated Hydrocarbon Contamination in Foods containing Vegetable Oil
Paola Dugo, Luigi Mondello, Peter Q. Tranchida, Mariosimone Zoccali Jan 1, 2012 | LCGC Europe<< Read Abstract >>This article describes a rapid heart-cutting liquid chromatography-gas chromatography (LC-GC) method for the analysis of mineral oil saturated hydrocarbons (MOSHs) found in a range of widely-consumed foods, including crisps, margarine, tinned tuna and vegetable oils.
The automated LC-GC experiments were performed using a system equipped with a syringe-type interface capable of both heart-cutting and comprehensive two-dimensional analysis. The first dimension separation was achieved on a silica column operated under isocratic conditions using hexane. The heart-cuts were then transferred to a programmed temperature vaporizer. After the large volume injection (LVI), the target analytes were rapidly separated (~ 9 min) using a micro-bore GC capillary column. The overall LC-GC run time enabled the analysis of around four samples in an hour. Various degrees of MOSH contamination - ranging from "not detected" to around 390 mg/kg - were discovered in the thirty samples that were subjected to analysis.
- Organic molecular markers and signature from wood combustion particles in winter ambient aerosols: aerosol mass
spectrometer (AMS) and high time-resolved GC-MS measurements in Augsburg, Germany
M. Elsasser, M. Crippa, J. Orasche, P. F. DeCarlo, M. Oster, M. Pitz, T. L. Gustafson, J. B. C. Pettersson, J. Schnelle-Kreis, A. S. H. Prévôt, and R. Zimmermann Atmos. Chem. Phys. Discuss., 12, 4831-4 66, 2012<< Read Abstract >>The impact of wood combustion on ambient aerosols was investigated in Augsburg, Germany during a winter measurement campaign of a six-week period. Special attention was paid to the high time resolution observations of wood combustion with different mass spectrometric methods. Here we present and compare the results from an Aerodyne aerosol mass spectrometer (AMS) and gas chromatographic - mass spectrometric (GC-MS) analysed PM1 filters on an hourly basis. This includes source apportionment of the AMS derived organic mass by using positive matrix factorisation (PMF) and analysis of levoglucosan as wood combustion marker, respectively. In the measurement period nitrate and organics are the main contributors to the defined submicron particle mass with 28% and 35 %, respectively. To the latter wood combustion organic aerosol (WCOA) contributes 23% on average and 27% in the evening and night-time. Conclusively, wood combustion has a strong influence on the organics and overall aerosol composition. Levoglucosan accounts for 14% of WCOA mass with a higher percentage in comparison to other studies. The ratio between the mass of levoglucosan and organic carbon amounts to 0.06. This study is unique in the one-hour time resolution comparison between the wood combustion results of the AMS and the GC-MS analysed filter method at a PM1 particle size range. This comparison of the concentration courses of the PMF WCOA factor, levoglucosan estimated by the AMS data and the levoglucosan measured by GC-MS is highly correlated, and a detailed discussion on the contributors to the wood combustion marker ion at mass-to-charge ratio 60 will be given. This offers a suitable application possibility for the description of the wood combustion course by the WCOA factor and the levoglucosan concentration estimated by AMS data. However, quantitative description of the levoglucosan concentration estimated by the AMS data is difficult due to the offset of latter compared to measured levoglucosan by the GC-MS.
- Ionic Liquid Stationary Phases: Application in Gas Chromatographic Analysis of Polar Components of Fuels and Lubricants
Sam Whitmarsh Chromatography Today, February / March 2012<< Read Abstract >>The capillary gas chromatographic analysis of polar components within fuels and lubricants was investigated using commercially available ionic liquid coated columns. The improved temperature stability and high polarity of these phases relative to polyethylene glycol were studied in one and two dimensions. In one dimension, the reduction in hydrocarbon matrix interference presents opportunities for improved quantitation and less sample preparation. In two dimensions, a reduction in second dimension retention was observed as phase polarity was increased providing a reminder that column sets should be correctly matched to sample composition for effective separation.
- Isotope fractionation of volatile organic compounds in porous media under variably saturated conditions
<< Read Abstract >>Keywords:
Carbon and chlorine isotope analysis, chlorinated ethenes, unsaturated zone, vaporization, diffusion, air-water partitioning, biodegradation
PhD thesis evaluation committee:
Daniel Hunkeler, Professor (thesis director), University of Neuchâtel, Switzerland
Mette Martina Broholm, Associate professor, Technical University of Denmark
Olivier Atteia, Professor, University of Bordeaux, France
Philip Brunner, Professor, University of Neuchâtel, Switzerland
- Validation of Biomarkers for Distinguishing Mycobacterium tuberculosis from Non-Tuberculous Mycobacteria Using Gas Chromatography-Mass Spectrometry and Chemometrics.
Dang NA, Kuijper S, Walters E, Claassens M, van Soolingen D, Vivo-Truyols G, Janssen HG, Kolk AH. 2013 Oct 17;8(10):e76263. doi: 10.1371/journal.pone.0076263<< Read Abstract >>Abstract
Tuberculosis (TB) remains a major international health problem. Rapid differentiation of Mycobacterium tuberculosis complex (MTB) from non-tuberculous mycobacteria (NTM) is critical for decisions regarding patient management and choice of therapeutic regimen. Recently we developed a 20-compound model to distinguish between MTB and NTM. It is based on thermally assisted hydrolysis and methylation gas chromatography-mass spectrometry and partial least square discriminant analysis. Here we report the validation of this model with two independent sample sets, one consisting of 39 MTB and 17 NTM isolates from the Netherlands, the other comprising 103 isolates (91 MTB and 12 NTM) from Stellenbosch, Cape Town, South Africa. All the MTB strains in the 56 Dutch samples were correctly identified and the model had a sensitivity of 100% and a specificity of 94%. For the South African samples the model had a sensitivity of 88% and specificity of 100%. Based on our model, we have developed a new decision-tree that allows the differentiation of MTB from NTM with 100% accuracy. Encouraged by these findings we will proceed with the development of a simple, rapid, affordable, high-throughput test to identify MTB directly in sputum.
- The identification of biomarkers differentiating Mycobacterium tuberculosis and non-tuberculous mycobacteria via
thermally assisted hydrolysis and methylation gas chromatography-mass spectrometry and chemometrics
Ngoc A. Dang, Arend H. J. Kolk, Sjoukje Kuijper, Hans-Gerd Janssen, Gabriel Vivo-Truyols 04/2013; 9(6):1274-1285. DOI:10.1007/s11306-013-0531-z<< Read Abstract >>ABSTRACT:
Infections with non-tuberculous mycobacteria (NTM) are increasing, particularly among immune-compromised patients and those with damaged lungs. Mycobacterium tuberculosis complex (MTB) strains, however, remain the most common cause of mycobacterial infection. A rapid method of distinguishing MTB from NTM is required for correct diagnosis and tuberculosis management. We have developed an automated procedure based on thermally-assisted hydrolysis and methylation followed by gas chromatography-mass spectrometry (THM-GC-MS) and advanced chemometrics to differentiate MTB from NTM. We used early cultures of mycobacteria in this first step towards the direct identification of these bacteria in sputum using a hand-held portable device. To build a classification model, we used 44 strains including 15 MTB and 29 NTM. A matrix of the aligned dataset containing ~45,700 features (retention time/mass pairs) for the 44 observations was submitted to partial least squares discriminant analysis (PLS-DA). We could reduce the number of features down to 250 without compromising the accuracy of the model. Twenty different compounds were found through mass spectral interpretation of these 250 features. Some of these compounds have not been linked to tuberculosis before, others have been proposed previously as diagnostic biomarkers for this disease. We have built a final model based on our proposed biomarkers that performed with 95 % accuracy in distinguishing MTB from NTM in early cultures. Since all these biomarkers have been chemically identified, work can proceed towards the development of simpler, bed-side diagnostic tests to differentiate MTB from NTM in sputum.
- Rapid diagnosis of TB using GC-MS and chemometrics (Review)
Ngoc A Dang, Hans-Gerd Janssen & Arend HJ Kolk December 2013, Vol. 5, No. 24, Pages 3079-3097 , DOI 10.4155/bio.13.288<< Read Abstract >>Abstract
The search continues for a rapid diagnostic test for TB that has high sensitivity and specificity and is useable in sophisticated environments and in deprived regions with poor infrastructure. We discuss here the modern bioanalytical techniques that can be used to discover biomarkers of infection with Mycobacterium tuberculosis, focusing on techniques using GC. We will also discuss the use of GC-MS to identify volatile organic compounds in the headspace of bacterial culture or in samples of breath, serum or urine. Biomarkers discovered in the ‘clean’ environment of culture may differ from those in patients. A number of biomarkers have been found in patients, with little consistency in the various studies to date. Reproducibility is difficult; the impressive results found initially with a few patients are rarely repeatable when a larger sample series is tested. Mycobacterial lipids offer promise for distinguishing M. tuberculosis from nontuberculous mycobacteria directly in sputum.
- Determination of polychlorinated biphenyls and organochlorine pesticides in small volumes of human blood by high-throughput on-line SPE-LVI-GC-HRMS
Jürgen Wittsiepe, Marco Nestola, Matthias Kohne, Peter Zinn, Michael Wilhelm Journal of Chromatography B, Volumes 945-946, 15 January 2014, Pages 217-224<< Read Abstract >>Abstract
A fully automated and robust method featuring on-line solid-phase extraction (SPE) and large volume injection (LVI) gas chromatographic (GC) high resolution mass spectrometry (HRMS) is used to determine polychlorinated biphenyls (PCBs) and organochlorine pesticides, such as penta- and hexachlorobenzene (PeCBz, HxCBz), hexachlorocyclohexane isomers (HCH) and 4,4´-dichlorodiphenyldichloroethene (a metabolite of dichlorodiphenyltrichloroethane (DDT)), with only 200 µl of human blood, serum or plasma. After spiking the sample with 13C-labeled internal standards and precipitating the proteins, the sample is passed through a 10 mm x 2.0 mm ID SPE cartridge filled with C18 material that adsorbs the analytes. After washing and drying, the cartridge is extracted with hexane/dodecane (99/1, v/v); the extract is directly injected into a LVI where GC/HRMS analysis follows. The fully automated system utilizes a robotic autosampler and a modular SPE system including two high-pressure syringe pumps, an automatic SPE cartridge exchanger unit and 6 switchable valves. All sample preparation steps are performed within 20 min during the GC run of a previous sample, limiting the throughput with only the GC runtime. The contents are quantified using the isotope dilution method. Due to laboratory air contamination problems, we achieved LOQs of 0.017 (PeCBz), 0.009 (HxCBz), 0.007 (HCH), 0.016 (DDE), while for the six indicator PCBs, we achieved values of 0.030 (PCB-28), 0.044 (PCB-52), 0.024 (PCB-101), 0.009 (PCB-138), 0.015 (PCB-153) and 0.008 (PCB-180) µg/l serum. Under clean laboratory air conditions, these values may be improved. This method is recommended when high throughput is desirable and/or only small amounts of material are available, such as during studies involving children.
On-line solid phase extraction; Large volume injection; Gas chromatography; Mass spectrometry; Human blood; Polychlorinated biphenyls; Organochlorine pesticides
- Direct detection of Mycobacterium tuberculosis in sputum using combined solid phase extraction-gas chromatography-mass spectrometry
Ngoc A. Dang, Marta Mourão, Sjoukje Kuijper, Elisabetta Walters, Hans-Gerd Janssen, Arend H.J. Kolk Journal of Chromatography B, Volumes 986-987, 1 April 2015, Pages 115-122<< Read Abstract >>Abstract
Recently, thermally-assisted hydrolysis and methylation followed by gas chromatography mass spectrometry (THM-GC-MS) in combination with chemometrics has been used to develop a 20-compound model for fast differentiation of Mycobacterium tuberculosis (MTB) from Non-tuberculous mycobacteria (NTM) in bacterial cultures. This model provided better than 95% accuracy. In our current work a hexane/methanol/water extraction followed by a solid phase extraction (SPE) clean-up procedure was developed for use before THM-GC-MS, to make the test suitable for the identification of mycobacteria in sputum. An algorithm was established based on tuberculostearic acid, hexacosanoic acid and mycoserosates. The detection limit of the method was approximately 1 x 104 bacteria/mL sputum. Sputum specimens from 32 patients from South Africa who were suspected of having tuberculosis were blindly tested using the new method. Eight of the nine culture-positive sputum specimens were detected by the new SPE-THM-GC-MS method, resulting in a sensitivity of 89%. The specimen that was missed by the new method was also microscopy negative. The specificity of the test was 100%; all 23 microscopy- and culture-negative specimens were correctly identified as negative by SPE-THM-GC-MS.
Mycobacterium tuberculosis; Direct detection; Sputum; Solid phase extraction; Gas chromatography-mass spectrometry.
- Quantitative pyrolysis - gas chromatography - mass spectrometry to study polymer dissolution and solubility
Aleksandra Chojnacka Thesis book ISBN: 978-94-6295-169-3<< Read Abstract >>Abstract
The combinations of pyrolysis (Py) with mass spectrometry (MS), gas chromatography with flame-ionization detection (GC-FID), and GC-MS have developed into very powerful tools to study different types of polymeric samples. Pyrolysis techniques may be conveniently used to study thermal stability and degradation products, polymer structure and composition, additives, low-molecular-weight constituents, etc. Because of the disperse nature of polymeric materials, detailed characterization often requires a combination of deferent techniques, such as liquid chromatography (LC) or size-exclusion chromatography (SEC) and Py-GC-MS. Quantitative pyrolysis is a relatively recent development and in this thesis it is used for the first time to study solubility.
- On the applicability of comprehensive two-dimensional gas chromatography combined with a fast-scanning quadrupole mass
spectrometer for untargeted large-scale metabolomics
Christoph H. Weinert, Björn Egert, Sabine E. Kulling Journal of Chromatography A: 1405 (2015) 156-167<< Read Abstract >>Abstract
Comprehensive two-dimensional gas chromatography mass spectrometry (GC x GC-MS) offers excellent chromatographic separation performance and superior sensitivity. As such, it is eminently suitable for the analysis of complex biological samples. The applicability of a GC x GC instrument equipped with a fastscanning qMS detector for large-scale untargeted metabolome analyses was investigated. We optimized the dimensions of an apolar x medium-polar column combination in order to meet detector requirements and to compromise between separation performance and analysis time. The final method enabled a sufficient separation (R = 1.2 or higher) of approx. 90% of all analytes detected in urine within less than 1 h. Using the qMS at maximum scan speed (20,000 u/s) and choosing a scan range of m/z 60-550, a data acquisition frequency of 33 Hz and usually at least 10-13 data points per 2D peak above the baseline were achieved. Peak area as well as peak height could thus be determined precisely (mean RSD 2.5%). Spectral skewing was limited regarding the data points covering the upper peak half. As a consequence, peak apex spectra could be used for the alignment of analytes in different samples. The linear dynamic range was 1-2.5 orders of magnitude, depending on the analyte. In addition, the slow transition into saturation beyond the linear dynamic range made it possible to exploit an extended “working range” for relative quantification. Long-term stability of the system was demonstrated by the analysis of more than 300 human urine study samples for which detailed repeatability and intermediate precision data are provided. In summary, the GC x GC-qMS system proved to be applicable for untargeted large scale metabolome analyses.
- Optimization of a large-volume injection method for compound-specific isotope analysis of polycyclic aromatic compounds at trace
Michaela Blessing, Maik A. Jochmann, Stefan B. Haderlein and Torsten C. Schmidt Rapid Commun. Mass Spectrom. 2015, 29, 2349-2360<< Read Abstract >>Abstract
Compound-specific isotope analysis (CSIA) of persistent organic contaminants can be used for source apportioning in the environment if appropriate sensitivity can be achieved. This paper describes the optimization and validation of a sensitive analytical approach for the determination of the carbon isotope composition of semi-volatile organic compounds, such as polycyclic aromatic hydrocarbons (PAHs).
Analyses are based on the introduction of up to 150µL of organic extracts by means of programmed temperature vaporization-large-volume injection combined with gas chromatography coupled to isotope ratio mass spectrometry (PTV-LVI-GC/IRMS). To allow for the analysis of more volatile, low-molecular-weight PAHs, the PTV injector was equipped with a sub-ambient/cryogenic cooling. Accuracy, precision, linearity and determination limits for application in isotope analysis were evaluated for a set of individual PAHs ranging from two- to five-ring molecular structures. The method was exemplified by determining the ð13C values of individual PAHs in soil samples in a source apportionment study at a contaminated site.
The choice of PTV injection parameters is crucial to prevent isotope fractionation during injection and largely depends on the analytes to be determined. The observed isotope fractionation effect on semi-volatiles depends on the applied solvent and injection temperature and demonstrates the importance of performing appropriate tests with given PTV parameters for each of the compounds of interest. The proposed PTV-LVI-GC/IRMS method allows the carbon isotope ratio (ð13C value) of individual PAHs to be determined accurately and precisely at concentrations of 0.04-0.1 ng µL-1 even for volatile PAHs such as naphthalene or acenaphthene.
LVI with PTV injector cooling allows for the isotopic analysis of volatile and semi-volatile PAHs at trace concentrations, thus considerably expanding the applicability of CSIA in environmental studies.
- Direct detection of Mycobacterium tuberculosis in sputum: A validation study using solid phase extraction-gas
Marta P.B. Mourão, Sjoukje Kuijper, Ngoc A. Dang, Elisabetta Walters, Hans-Gerd Janssen, Arend H.J. Kolk Journal of Chromatography B, 1012 (2016) 50-54<< Read Abstract >>Tuberculosis (TB) remains a worldwide health problem, especially in developing countries. Correct identification of Mycobacterium tuberculosis (MTB) infection is extremely important for providing appropriate treatment and care to patients. Here we describe a solid phase extraction-gas chromatography-mass spectrometry method (SPE-THM-GC-MS) for the detection of five biomarkers for M. tuberculosis. The method for classification is developed and validated through the analysis of 112 sputum samples from patients suspected of having TB. Twenty of twenty-five MTB culture-positive sputum samples were correctly classified as positive by our improved SPE-THM-GC-MS method. Eighty-five of eighty-seven MTB culture-negative samples were also negative by SPE-THM-GC-MS. The overall sensitivity of the new SPE-THM-GC-MS method is 80% (20/25) and the specificity is 98% (85/87) compared with culture. The method proved to be reliable and, although complex in principle, easy to operate due to the high degree of automation.
- On-Line Combination of High Performance Liquid Chromatography with Comprehensive Two-Dimensional Gas
Chromatography-Triple Quadrupole Mass Spectrometry: A Proof of Principle Study
Mariosimone Zoccali, Peter Quinto Tranchida, and Luigi Mondello Anal. Chem., 2015, 87 (3), pp 1911-1918. DOI: 10.1021/ac504162a<< Read Abstract >>The present contribution is focused on the on-line combination of high performance liquid chromatography (HPLC), cryogenically modulated comprehensive two-dimensional gas chromatography (GC x GC), and triple quadrupole mass spectrometry (QqQ MS), generating a very powerful unified separation-science tool. The instrument can be used in seven different combinations ranging from one-dimensional HPLC with a photodiode array detector to on-line LC x GC x GC/QqQ MS. The main focus of the present research is directed to the LC-GC x GC/QqQ MS configuration, with its analytical potential shown in a proof-of-principle study involving a very complex sample, namely, coal tar. Specifically, a normal-phase LC process enabled the separation of three classes of coal tar compounds: (1) nonaromatic hydrocarbons; (2) unsaturated compounds (with and without S); (3) oxygenated constituents. The HPLC fractions were transferred to the GC x GC instrument via a syringe-based interface mounted on an autosampler. Each fraction was subjected to a specific programmed temperature vaporizer GC x GC/QqQ MS untargeted or targeted analysis. For example, the coal tar S-containing compounds were pinpointed through multiple-reaction-monitoring analysis, while full-scan information was attained for the oxygenated constituents.
- Improvement of mineral oil saturated and aromatic hydrocarbons determination in edible oil by liquid-liquid-gas
chromatography with dual detection
Mariosimone Zoccali,Laura Barp,Marco Beccaria,Danilo Sciarrone,Giorgia Purcaro, Luigi Mondello Journal of Separation Science V.39, Issue 3 February 2016 Pages 623-631, DOI: 10.1002/jssc.201501247<< Read Abstract >>Mineral oils, which are mainly composed of saturated hydrocarbons and aromatic hydrocarbons, are widespread food contaminants. Liquid chromatography coupled to gas chromatography with flame ionization detection represents the method of choice to determine these two families. However, despite the high selectivity of this technique, the presence of olefins ( particularly squalene and its isomers) in some samples as in olive oils, does not allow the correct quantification of the mineral oil aromatic hydrocarbons fraction, requiring additional off-line tools to eliminate them. In the present research, a novel on-line liquid chromatography coupled to gas chromatography method is described for the determination of hydrocarbon contamination in edible oils. Two different liquid chromatography columns, namely a silica one (to retain the bulk of the matrix) and a silver-ion one (which better retains the olefins), were coupled in series to obtain the mineral oil aromatic hydrocarbons hump free of interfering peaks. Furthermore, the use of a simultaneous dual detection, flame ionization detector and triple quadrupole mass spectrometer allowed us not only to quantify the mineral oil contamination, but also to evaluate the presence of specific markers (i.e. hopanes) to confirm the petrogenic origin of the contamination.
- Analysis of the sesquiterpene fraction of citrus essential oils by using the off-line combination of high performance liquid chromatography and gas chromatography-based methods: a comparative study
Mariosimone Zoccali, Ivana L. Bonaccorsi, Peter Q. Tranchida, Paola Dugo, Luigi Mondello, Giovanni Dugo Flavour and Fragrance Journal, Volume 30, Issue 6 November 2015, Pages 411-422. DOI: 10.1002/ffj.3262<< Read Abstract >>The present investigation is based on the off-line combination of high-performance liquid chromatography (HPLC), with different high-resolution gas chromatography (GC) methods (LC//GC), for the analysis of the sesquiterpene hydrocarbon (SH) fraction of various Citrus essential oils. Attention was directed to such constituents because the SH profile is often highly specific and can vary considerably between different Citrus oil-types. The (normal phase) HPLC step was exploited for the separation of the hydrocarbons, from the oxygenated compounds, hence generating a simplified sub-sample. After, the hydrocarbon fraction was concentrated and subjected to analysis, using conventional GC-quadrupole mass spectrometry (qMS) and GC-flame ionization detection (FID), comprehensive two-dimensional GC-qMS and comprehensive two-dimensional GC-FID, and cold-injection GC-qMS. The latter approach was exploited to avoid and evaluate solute rearrangements occurring under hot-injection conditions. The data derived from each approach were compared, to evaluate each analytical approach. Apart from the comparative scopes, an overall highly-detailed view (both qualitative and quantitative) was attained on the SH fraction of each essential oil, with many constituents reported here for the first time.
- Analysis of Volatile Odor Components of Superheated Steam-cooked Rice with a Less Stale Flavor
Hatsuho Takemitsu, Midori Amako, Yoshihiro Sako, Kei Shibakusa, Koji Kita, Shinichi Kitamura, Hiroshi Inui Food Science and Technology Research. Vol. 22 (2016) No. 6 p. 771-778<< Read Abstract >>Milled common Japonica rice was cooked using a newly developed superheated steam rice cooking machine and the volatile odor compounds of the steamed rice and of the steam generated during cooking were analyzed. At least 22 odorous compounds were found in the steam by GC-olfactometry, of which 13 were identified by GC-MS. Hexanal and (E,E)-2,4-decadienal, which are known odor compounds characteristic of cooked rice, were identified, and four compounds, including longifolene and 2-methoxyphenol, were newly identified in Japonica rice. The amounts of hexanal and (E,E)-2,4-decadienal in steamed rice, extracted with methyl tert-butyl ether, were essentially the same as in ordinary cooked rice. On the other hand, headspace analysis showed that the levels of odor compounds in steamed rice were less than 10% that of ordinary cooked rice. Only small amounts of odorants appear to be released from the surfaces of steamed rice grains.
- Influence of electrolyte additives on the cathode electrolyte interphase (CEI) formation on LiNi1/3Mn1/3Co1/3O2 in half cells with Li metal counter electrode
Yunxian Qian, Philip Niehoff, Markus Borner, Martin Grützke, Xaver Monnighoff, Pascal Behrends, Sascha Nowak, Martin Winter, Falko M. Schappacher. Journal of Power Sources 329 (2016) 31-40<< Read Abstract >>Traditional solid electrolyte interphase (SEI) forming additives of vinylene carbonate (VC), fluoroethylene carbonate (FEC) and ethylene sulfite (ES) are studied with respect to their impact on the formation and growth of the cathode electrolyte interphase (CEI) layer. T-half cells are assembled and undergo three different electrochemical investigation plans: after formation (0.1C, 5 cycles) and long term cycling (0.1C, 5 constant current cycles þ 1C, 100/150 constant current/voltage cycles), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and gas chromatography-mass spectrometry (GC-MS) are combined to investigate morphology, CEI composition, CEI thickness and aging products for cells with different electrolyte systems. The obtained results reveal a significant in- fluence of these additives on the CEI composition and CEI growth. With the help of SEM, it is found that large areas of electrolyte decomposition products are formed at the aged electrode surfaces (¼after cycling), with the exception when 2 vol% of FEC is added into the reference electrolyte. From XPS measurements, CEI thicknesses are calculated. The reference electrolyte with 2 vol% of FEC shows the thinnest layer after long time aging (0.8 ± 0.2 nm). For the addition of 2 vol% of VC, an incremental growth of the CEI thickness occurs from the 100th to 150th cycle (from 1.0 ± 0.1 nm to 2.9 ± 0.4 nm). By correlating the CEI thickness values with the electrochemical performance, it can be observed that for lithium metal based half cells, the existence of a thinner CEI layer corresponds to a better cycling behavior, with 2 vol% of FEC showing the highest discharge capacity of 114.4 ± 0.2 mAh/g after 150 cycles at 1C. GC-MS shows that both VC and FEC help to prevent fast electrolyte aging
- Distinctive Lipid Composition of the Copepod Limnocalanus macrurus with a High Abundance of Polyunsaturated Fatty Acids
Minna Hiltunen, Ursula Strandberg, Markku Keinänen, Sami Taipale, Paula Kankaala. Lipids (2014) 49:919-932. DOI 10.1007/s11745-014-3933-4<< Read Abstract >>We studied the copepod Limnocalanus macrurus for seasonal variation in the composition of fatty acids, wax esters and sterols in large boreal lakes, where it occurs as a glacial-relict. Vast wax ester reserves of Limnocalanus were accumulated in a period of only two months, and comprised mono- and polyunsaturated fatty acids (PUFA) and saturated fatty alcohols. In winter, the mobilization of wax esters was selective, and the proportion of long-chain polyunsaturated wax esters declined first. PUFA accounted for [50 % of all fatty acids throughout the year reaching up to ca. 65 % during late summer and fall. Long-chain PUFA 20:5n-3 and 22:6n-3 together comprised 17-40 % of all fatty acids. The rarely reported C24 and C26 very-longchain PUFA (VLC-PUFA) comprised 6.2 ± 3.4 % of all fatty acids in August and 2.1 ± 1.7 % in September. The VLC-PUFA are presumably synthesized by Limnocalanus from shorter chain-length precursors because they were not found in the potential food sources. We hypothesize that these VLC-PUFA help Limnocalanus to maximize lipid reserves when food is abundant. Sterol content of Limnocalanus, consisting ca. 90 % of cholesterol, did not show great seasonal variation. As a lipid-rich copepod with high abundance of PUFA, Limnocalanus is excellent quality food for fish. The VLC-PUFA were also detected in planktivorous fish, suggesting that these compounds can be used as a trophic marker indicating feeding on Limnocalanus.