Quantification of tamoxifen and N-desmethyltamoxifen in human plasma by high-performance liquid chromatography, photochemical reaction and fluorescence detection, and its application to biopharmaceutic investigations.

The anticancer drug tamoxifen and its major metabolite N-desmethyltamoxifen are quantified in human plasma down to subnanogram amounts by high-performance liquid chromatography. Plasma is alkali-buffered and extracted with hexane. The organic solvent is evaporated and the residue dissolved in the mobile phase. An aliquot is sampled automatically and chromatographed. The analytes are detected after postcolumn UV irradiation and rearrangement to substituted phenanthrenes by their intense fluorescence. Precise handling of exact volumes facilitates external calibration. Statistical data for precision and accuracy are given and illustrate reliable quantification. The method is applied to the samples of a clinical study, and the pharmacokinetic parameters of both analytes are presented. The novel design of the photochemical reactor is discussed, with respect to peak broadening and photochemical recovery. The measured peak broadening is smaller than theoretically predicted, owing to non-helical coiling.