GCMS Ions, what is what

ions (m/z)

Compound

Possible Source

13,14,15,16

Methane

CI gas

18, 28, 32, 44 or 14, 16

H2O, N2, O2, CO2 or N, O

Residual air and water, air leaks, outgassing from Vespel ferrules

31, 51, 69, 100, 119, 131, 169,
181, 214, 219, 264, 376, 414,
426, 464, 502, 576, 614

PFTBA and related ions

PFTBA (tuning compound)

31

Methanol

Cleaning solvent

43, 58

Acetone

Cleaning solvent

78

Benzene

Cleaning solvent

91, 92

Toluene or xylene

Cleaning solvent

105, 106

Xylene

Cleaning solvent

151, 153

Trichloroethane

Cleaning solvent

69

Foreline pump fluid or PFTBA

Foreline pump oil vapor or calibration valve leak

73, 147, 207, 221, 281,
295, 355, 429

Dimethylpolysiloxane

Septum bleed or methyl silicone column coating

77, 94, 115, 141, 168, 170,
262, 354, 446

Diffusion pump fluid

Diffusion pump fluid and related ions

149

Plasticizer (phthalates)

Vacuum seals (O-rings) damaged by high temperatures, use of vinyl or plastic gloves

Peaks spaced 14 amu apart

Hydrocarbons

Fingerprints, fore line pump oil