The double radio-isotope derivative techniques for the assay of drugs in biological material

The neuroleptic drug opipramol and its deshydroxyethyl metabolite can be determined simultaneously in the same biological sample. Known amounts of 14C-labelled opipramol and 14C-labelled metabolite are added to the sample to serve as internal standards. After suitable extraction, both compounds are acetylated by 3H-labelled acetic anhydride. Together with μg-amounts of carrier compounds, the O-acetyl derivative of opipramol and the N-acetyl derivative of the metabolite are purified and separated by two-dimensional thin-layer chromatography. Each of the derivatives is isolated and counted for 14C- and 3H-activity. The 14C-activities recovered serve to determine the overall yield of the opipramol and metabolite, and to convert the measured 3H-activity to 100% theoretical yield. From analyses of standard samples, the specific 3H-activities of the acetyl derivatives were calculated and these values were used to convert the measured 3H-activites from biological samples to concentrations of original opipramol and metabolite. For both compounds the standard deviations of blank samples were +- 1 ng/ml. For concentrations up to 100 ng/ml the standard deviation was +- 3 ng/ml