The utility of combined gas chromatography-mass spectrometry is now well established for analysis of compounds of biological importance. For successful gas chromatography, it is often necessary to form derivatives of the compounds of interest. For the combined technique, both chromatographic and mass spectrometric requirements must be considered, ease of recognition of the mass spectrum and ease of chromatographic separation being of equal importance in the choice of derivative.
We report here a comparative study of the mass spectra of the common derivatives of the "classical" estrogens and assess the suitability of these derivatives for use in combined gas chromatography-mass spectrometry.
EXPERIMENTAL
A modified Research Specialties model 600 gas chromatograph, equipped with a flame ionization detector, and an Hitachi RMUGE singlefocusing mass spectrometer were used. The instruments were joined by means of a silver membrane molecular separator (1) either alone or in series with a silicone membrane separator (Varian model V-5620).
Derivatives were prepared by established methods (2) and purity was determined by gas chromatography. All samples used for mass spectrometry were at least 95% pure.
Mass spectra were recorded from 10 pg samples admitted through the solid introduction system with the following instrument conditions: sample temperature 150ยฐC; ion source temperature 250ยฐC; electron energy 7OV, ionizing current 50 PA.
Comparison showed no significant differences between spectra obtained by direct injection and those obtained using the combined instrument.
RESULTS
AND DISCUSSION
The characteristic spectra of the estrogens are due mainly to cleavage of benzylic bonds arising from the presence in the molecule of the aro-1