Simultaneous measurement of imipramine and desipramine by selected ion recording with deuterated internal standards.

A gas chromatographic mass spectrometric method for the quantitative determination of imipramine and its N-demethylated metabolite desipramine in plasma samples at the nanogram level is reported. The method involves derivatization of the extracted drugs with trifluoroacetylimidazole, a mild derivatizing reagent. Specificity is provided by selected ion recording of the [M + H]+ ions, formed upon chemical ionization with methane as reagent gas. Quantitation is achieved by stable isotope dilution techniques, using deuterium labeled analogs, prepared by acid-catalyzed exchange, as internal standards. Data on patient samples are presented.