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SUMMARY It has recently been shown that mass fragmentography may serve as a powerful tool in the field of steroid biochemistry. This is demonstrated by the following examples. When [4-14C]oestriol was incubated with liver slices of wild mice, about 50 ng of a polar radioactive metabolite were isolated. Despite the small amount of steroid and impurities present in the extract, the unknown metabolite was identified as 6-hydroxyoestriol by the technique of single ion monitoring, using g.l.c. columns of different polarity. Furthermore, mass fragmentography provides a simple and highly specific method for the determination of steroid hormones in body fluids. Using the single ion technique, the amount of steroid is calculated by comparing the peak areas of the sample and of the standard. This method can be considerably improved by the use of steroids labelled with stable or radioactive isotopes as internal standards. The determination is performed by comparing the peak areas of the steroid to be quantitated and of the isotopically labelled steroid: measurement of the peaks is achieved by monitoring two m/e values simultaneously (multiple ion detection). This procedure has been applied to the specific determination of oestrogens, testosterone, aldosterone and tetrahydroaldosterone in plasma and/or urine. The sensitivity of mass fragmentography can be increased by using the heptafluorobutyric esters of the various steroids.

Mass fragmentography may serve as a powerful tool in the fields of steroid biochemistry and clinical chemistry; it provides a simple and highly specific method for the determination of steroids in body fluids. Isotopically labelled steroids, corresponding to the natural occurring steroids, may be used as internal standards in order to correct for procedural losses as well as adsorption effects on the gas chromatographic columns. Since the mass spectrometer is capable of separating isotopes, quantitative determinations may be performed by comparing the peak areas of the unlabelled and the isotopically labelled steroids; the peaks are recorded simultaneously by monitoring two m/e-values (multiple ion detection). With respect to sensitivity and specificity, the method may be considerably improved by the use of special derivatives, e.g. heptafluorobutyrates. Because of their high specificity, determinations by mass fragmentography will be increasingly used as reference methods in the field of steroid hormones. In the present paper the procedure has been applied to the specific determination of oestrogens, testosterone, 5α-dihydrotestosterone, cortisol and aldosterone in human plasma.