Determination of clomipramine and desmethyl-clomipramine in plasma or urine by the double-radioisotope derivative technique.

A double radioisotope derivative method was developed for the determination of clomipramine and desmethyl-clomipramine in plasma or urine. After addition of 14C-labeled clomipramine and desmethyl-clomipramine as internal standards and extractive isolation of both compounds, desmethyl-clomipramine is acetylated with [3H]acetic anhydride. The [3H]acetamide is separated from clomipramine by thin-layer chromatography and its radioactivity is measured. Clomipramine, extracted from the cilica gel, is reacted with trichloroethyl chloroformate. The urethane is saponified and decarboxylated. The resulting desmethyl-clomipramine is acetylated with [3H]acetic anhydride. The [3H]acetamide is purified by thin-layer chromatography and its radioactivity is measured. The sensitivity of the method is 15 mug/liter for clomipramine and 2 mug/liter for desmethyl-clomipramine. Its specificity was made sure by a cross-check with a gas chromatography-mass spectrometry technique.