Estradiol-17 beta determined in plasma by gas chromatography-mass spectrometry with selected ion monitoring of mixed silyl ether-perfluoroacyl ester derivatives and use of various stable-isotope-labeled internal standards.

A highly specific method is described for measuring estradiol-17 beta (E2) in plasma by gas chromatography-mass spectrometry (GC-MS) associated with stable isotope dilution. A mixed derivative, E2-3-trimethylsilyl ether-17-heptafluorobutyrate (E2-3-TMS-17-HFB), was found to have excellent analytical properties. The specificity of the derivatization procedure exploits a unique feature of estrogens: the selective exchange of a phenolic perfluoroacyl ester for a trialkylsilyl ether. No significant differences in E2 concentration could be ascribed to the use of 2H- or 13C-labeled analogs, thus ruling out interferences from possible isotope exchange commonly attributed to deuterated compounds. Precision is closely similar to that for methods in which the more common E2-3, 17-bis(trimethylsilyl) ether and E2-3, 17-bis(heptafluorobutyrate) derivatives are used. Sensitivity and specificity of the mixed 3-TMS-17-HFB derivative allow adequate determinations of E2, even in plasma from males, in 2-mL samples. Interlaboratory mean concentrations of E2 obtained by routine immunoassays were consistently higher than the target values estimated by GC-MS, particularly at concentrations less than 100 pmol/L.