Determination by liquid chromatography-mass spectrometry of clomiphene isomers in the plasma of patients undergoing treatment for the induction of ovulation.

A rapid, sensitive and selective LC-MS method is described for the simultaneous determination of zuclomiphene and enclomiphene in plasma from patients undergoing treatment with clomiphene citrate for the induction of ovulation. Samples spiked with N-didesmethyltamoxifen, the internal standard, were extracted into methyl tertiary butyl ether. The compounds were separated on a Luna C(18) analytical column, and a mobile phase of methanol-water (70:30 v/v) containing 0.05% trifluoroacetic acid at a flow rate of 1ml/min. The limits of determination were 35pg/ml and 7pg/ml for zu- and enclomiphene, respectively. Within-day coefficients of variation ranged from 2.1% to 7.2%.