Optimizing high-performance liquid chromatography method with fluorescence detection for quantification of tamoxifen and two metabolites in human plasma: application to a clinical study.

We set an improved high-performance liquid chromatography method with fluorescence detection HPLC-FLU assay with more sensitivity and precision for the quantification of tamoxifen and two metabolites: 4-hydroxytamoxifen and N-desmethyltamoxifen. The compounds and internal standard, mexiletine, were separated with an Agilent Extend C18 column set at 65 degrees C and a mobile phase of methanol-1% triethylamine aqueous solution (pH 11; 82:18, v/v). The detection system utilized offline ultraviolet irradiation to convert the analytes to their respective photocyclisation products, followed by fluorescence detection (lambda ex=260 nm and lambda em=375 nm). The limits of quantification for tamoxifen, N-desmethyltamoxifen and 4-hydroxytamoxifen in plasma were improved to 0.5, 0.5 and 0.1 ng/ml, respectively. And the retention times for tamoxifen, N-desmethyltamoxifen and 4-hydroxytamoxifen were minimized to 11, 10 and 3.9 min, respectively. A single stage liquid-liquid extraction method for determination of these triphenylethylene drugs in plasma was developed, with high extraction efficiency and rapid sample treatment for target compounds. The method has been validated for use in a clinical bioavailability research of tamoxifen.