- 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.
- 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
(LV-DMI-GC-TOF-MS)
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%.
- 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%.
- 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).
- 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.
- 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.
- Organische Verbindungen in Feinstaub (German language)
Nachrichten aus der Chemie, 54, Juni 2006, 676
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Rapid Multidimensional Liquid-Gas Chromatography for the Analysis of Saturated Hydrocarbon Contamination in Foods containing Vegetable Oil
<< 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.
- In-situ derivatization thermal desorption GC-TOFMS for direct analysis of particle-bound non-polar and polar organic species
<< 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.
- 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
<< 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.
- Capabilities of Direct Sample Introduction-Comprehensive Two-Dimensional Gas Chromatography-Time-of-Flight Mass Spectrometry to Analyze
Organic Chemicals of Interest in Fish Oils
<< 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
<< 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.
