Selected ion monitoring assay for the antidepressant mianserin in human plasma with stable isotope labeled analog as internal standard.

A quantitative gas chromatographic/mass spectrometric (GC/MS) assay was developed for the determination of Mianserin in human plasma. The assay utilizes selected ion monitoring in a GLC effluent, the molecular ion of Mianserin generated by electron impact ionization. Mianserin-d3, site specific, was synthesized and used as an internal standard. The assay can measure 5 ng/mL of drug with about 5% precision. The curve relating the amounts of drug added to control plasma versus the ion intensity ratio at m/e 264-267 is a straight line with a slope of 0.99 + 0.02 and zero intercept. The method was used for the analysis of drug in plasma of patients maintained on Mianserin therapy. Assay specificity was confirmed by complete identity of the mass spectrum of Mianserin in the biological extract with that of the authentic material.