Unexpected peaks in electron ionisation mass spectra of trimethylsilyl derivatives resulting from the presence of trace amounts of water and oxygen in gas chromatography/quadrupole time-of-flight systems.

Abstract

Silylation is one of the most prevalent derivatization method. Replacement of active hydrogen (in-OH,-SH or =NH groups) by a silyl group reduces the polarity of the compound and hydrogen bonding 1. Electron ionization (EI) mass spectra of trimethylsilyl ethers or esters exhibit a significant [M-15] + ion formed by loss of a methyl group bonded to silicon, which is very useful in determining the molecular mass. EI mass spectra of trimethylsilyl (TMS) derivatives may be employed not only for molecular weight determinations, but also for structural deductions. 2 They are generally stable during GC-MS analyses, although contamination of the mass spectrometer source with organic substances has been reported to cause some decomposition. 3 Moreover, it may be noted that if the amount of water is too high