Degradation of steroid derivatives at a gas chromatograph mass spectrometer interface

Abstract

Methyloxime trimethylsilyl ether derivatives are frequently employed in gas chromatographic and mass spectrometric analysis of steroids. Under certain instrumental conditions, unusual mass spectra were recorded from some corticosteroid methyloxime trimethylsilyl ether derivatives, reflecting degradation by contact of the steroids with active surfaces in the gas chromatograph mass spectrometer interface. This occurred prior to electron impact ionization. Fragmentations of the degradation products of methyloxime trimethylsilyl ether derivatives of tetrahydrocortisol and tetrahydrodeoxycorticosterone are described, as representatives of C21 steroids with dihydroxyacetone and α-ketol side chains. Elemental compositions of ions were confirmed by high resolution mass spectrometric analysis. Derivatives of steroids with glycerol side chains, e.g. cortolone, showed no evidence of degradation. The problem was overcome by ensuring inertness of the glass restrictor interface and by preventing, as far as posssible, contact of sample with metal surfaces in the source housing.