The following table provides guidance in the recognition and interpretation of potentially spurious signals (m/z peaks) that are sometimes observed in measured mass spectra (Ref. 1). Often, the occurrence of these signals can be predicted by the recent history of the instrument or the method being used. This is especially true if the mass spectrometer is interfaced to a gas chromatograph.
Ions observed, m/z | Possible compound | Possible source |
13, 14, 15, 16 | Methane* | Chlorine reagent gas |
18 | Water* | Residual impurity, outgassing of ferrules, septa, and seals |
14, 28 | Nitrogen* | Residual impurity, outgassing of ferrules, septa, and seals; leaking seal |
16, 32 | Oxygen* | Residual impurity, outgassing of ferrules, septa, and seals; leaking seal |
44 | Carbon dioxide* | Residual impurity, outgassing of ferrules, septa, and seals; leaking seal; note it may be mistaken for propane in a sample |
31, 51, 69, 100, 119, 131, 169, 181, 214, 219, 264, 376, 414, 426, 464, 502, 576, 614 | Perfluorotributylamine (PFTBA), and related ions** | This is a common tuning compound; may indicate a leaking valve |
31 | Methanol | Solvent; can be used as a leak detector |
43, 58 | Acetone | Solvent; can be used as a leak detector |
78 | Benzene | Solvent; can be used as a leak detector |
91, 92 | Toluene | Solvent; can be used as a leak detector |
105, 106 | Xylenes | Solvent; can be used as a leak detector |
151, 153 | Trichloroethane | Solvent; can be used as a leak detector |
69 | Rough (fore) pump fluid, PFTBA | Back diffusion of fore pump fluid, possible leaking valve of tuning compound vial |
73, 147, 207, 221, 281, 295, 355, 429 | Dimethylpolysiloxane | Bleed from a column or septum, often during high-temperature program methods in GC-MS |
77, 94, 115, 141, 168, 170, 262, 354, 446 | Diffusion pump fluid | Back diffusion from diffusion pump, if present |
149 | Phthalates | Plasticizer in vacuum seals, gloves |
X – 14 peaks | Hydrocarbons | Loss of a methylene group indicates a hydrocarbon sample |
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