MEASUREMENT OF PLASMA TESTOSTERONE BY GAS-CHROMATOGRAPHY NEGATIVE-IONMASS-SPECTROMETRY USING PENTAFLUOROPROPIONIC DERIVATIVES

Plasma testosterone was measured by gas chromatography-negative-ion ch emical ionisation mass spectrometry (GC-MS). The testosterone was extr acted from plasma using home-made Extrelut columns and diethyl ether e lution. It was quantified as the pentafluoropropionate (PFP) derivativ e by selected-ion monitoring at m/z 560 (testosterone) and 563 (d(3)-t estosterone), accounting for about 34% of the total ion. The character istics of the method were: extraction recovery about 95%; linearity ov er the range 1.7-71.5 nmol l(-1) with linear regression equation y = 1 .41x + 0.0217, r = 0.999; detection limit 3.5 fmol injected with a sig nal-to-noise ratio of 7.4; within-day variation, 3% for GC-MS, and 5.8 % for the whole process; day-to-day coefficient of variation, 6.6-11%, depending on the concentrations. There was a good correlation between the results obtained by GC-MS and RIA (r = 0.994), but the GC-MS valu es were significantly lower (p < 0.05) than those obtained by RIA.