The use of pentafluorobenzyloxime-trimethylsilyl derivatives in the analysis of corticosteroids by gas chromatography/negative ion chemical ionization mass spectrometry

Abstract

Pentafluorobenzyl hydroxylamine has been used as a derivatization reagent in the analysis of corticosteroids by gas chromatography/negative ion chemical ionization (GC/NICI) mass spectrometry. The resulting pentafluorobenzyloxime-trimethylsilyl (PFBO/TMS) derivatives were generally formed in moderate yield but, despite this, the use of these derivatives resulted in a ∼ 10-fold improvement in the capability of identification of corticosteroids by GC/NICI mass spectrometry in comparison with the methoxime/TMS derivatives previously employed. The NICI mass spectra of PFBO/TMS derivatives were simple, with most of the ion current being carried by the [M – C6F6CH2]−. or [M – PFB]−. ion and by a reagent-specific peak at m/z 196. The derivatives have been employed in the quantification of ∼400 pg amounts of endogenous hydrocortisone present in samples of human aqueous humour and are readily applicable to the determination of low-picogram amounts of these compounds in biological media.