Determination of an irreversible inhibitor of monoamine oxidase B (MDL 72974A) in human plasma and urine by gas chromatography-positive-ion chemical ionization mass spectrometry.

A sensitive and specific assay has been developed for the quantitative measurement in human plasma and urine of the irreversible inhibitor of monoamine oxidase B [(E)-4-fluoro-beta-fluoromethylenebenzene-butanamine HCl salt] (MDL 72974A) (I). This assay is based on gas chromatography-mass spectrometry with ammonia as the chemical ionization reagent gas. After addition of 1-fluoro-2-(4-chlorobenzene)-ethanamine HCl salt (MDL 71946A) as the internal standard, plasma (1 ml) and urine (100 microliter) samples were extracted using an automated solid-liquid extraction procedure on CN columns. The eluent was dried with a stream of nitrogen, and the residue was derivatized with pentafluoropropionic anhydride. Selected-ion monitoring of the [MNH4]+ ions m/z 361 (I) and 351 (internal standard) was used for quantification. The method yielded a linear response over the concentration range 0.25-100 pmol/ml in plasma with a limit of quantitation of 0.25 pmol/ml. The within-day reproducibility at a concentration of 5 pmol/ml was 4.6% and at a concentration of 50 pmol/ml was 1.3%. The day-to-day reproducibility was 5.2 and 7.0% at concentrations of 10 and 30 pmol/ml, respectively. The method was applied to the quantification of I in plasma and urine after the administration of 12-mg doses of I to a healthy male volunteer.