Diethylsilyl ether and diethylsiliconide derivatives in gas chromatography mass spectrometry of hydroxylated steroids

Abstract

The gas chromatographic and mass spectrometric properties of the diethylsilyl (DEHS) or diethylsiliconide (DES)-DEHS ether derivatives of 20 hydroxysteroids of various types have been studied using N,O-bis(diethylsilyl)trifluoroacetamide as a new silylating agent. The mass spectra of the DES-DEHS ether derivatives were characterized by their marked simplicity and by molecular ions of high abundance, whereas the mass fragmentation patterns of the DEHS ether derivatives without formation of the DES group in the molecule were similar to those of the corresponding dimethylethylsilyl (DMES) ether derivatives. The appearance of the molecular ion may be very useful for estimating the molecular weight of hydroxysteroids of which other silyl ether derivatives yield molecular ions of insufficient abundance to characterize them. In particular, the DES-DEHS ether derivative of 5β-pregnane-3α,17α,20α-triol gave the molecular ion at m/z 506 as a principal ion in the electron impact ionization mode. The methylene unit values of the DEHS ether derivatives of hydroxysteroids without formation of DES groups were slightly larger than those of the corresponding DMES ether derivatives. A Δ[Um]s value was presented for estimation of the number of siliconide moieties in the DES-DEHS ether derivatives.