Serum testosterone determination by mass fragmentography.

A mass fragmentographic reference method for the determination of plasma or serum testosterone is described. A fixed amount of [4--14C]testosterone (usually 10 ng) is added to a fixed amount of serum (usually 1 ml) and extracted with ether. The ether extract is purified by means of thin-layer chromatography. The purified testosterone is converted into the di-trimethylsilyl derivative by treatment with trimethylsilylimidazole. The amount of unlabeled testosterone is determined from the ratio between the recordings at m/e 432 and 434, obtained after analysis with a combined gas chromatograph-mass spectrometer equipped with a MID-unit (multiple ion detector). The two ions used correspond to the molecular peak in the mass spectrum of unlabeled and 4--14C-labeled testosterone, respectively. The relative standard deviation of the method was about 2.7 percent. The method was compared with a radioimmunoassay technique. There was a good correlation and the regression coefficient was about 0.83. A diurnal rhythm in testosterone secretion was confirmed both with the mass fragmentographic technique and with radioimmunoassay.