Stable isotope dilution negative ion chemical ionization gas chromatography-mass spectrometry for the quantitative analysis of paroxetine in human plasma

A sensitive and specific method for the quantitative determination of parox etine in human plasma is presented. After solvent extraction from plasma wi th hexane/ethyl acetate (1:1) at alkaline pH and derivatization to the pent afluorobenzyl carbamate derivative, paroxetine was measured by gas chromato graphy-negative ion chemical ionization mass spectrometry. The carboxylate anion at m/z 372 was obtained at high relative abundance. [H-2(6)]-labeled paroxetine was used as an internal standard and its rapid and facile prepar ation from the unlabeled compound is described. Calibration graphs were lin ear within a range of 0.094-12.000 ng ml(-1) using 1 ml of plasma and 0.469 -60 ng ml-1 using 200 mul of plasma. Intra-day precision was 1.47% (0.375 n g ml(-1)), 3.16% (3 ng ml(-1)) and 1.37% (9 ng ml(-1)) for the low-level me thod, and 3.37% (1.875 ng ml(-1)), 2.72% (15 ng ml(-1)) and 2.22% (45 ng ml (-1)) for the high-level method. Inter-day precision was 1.65% (0.375 ng ml (-1)), 2.13% (3 ng ml(-1)) and 1.66% (9 ng ml(-1)) for the low-level method , and 1.10% (1.875 ng ml(-1)), 1.56% (15 ng ml(-1)) and 1.90% (45 ng ml(-1) ) for the high-level method. At the limit of quantification (0.094 ng ml(-1 )), intra-day precision was 4.30% (low-level method) and 2.56% (high-level method), and inter-day precision was 3.23% (low-level method) and 3.00% (hi gh-level method). The method is rugged, rapid and robust and has been appli ed to the batch analysis of paroxetine during pharmacokinetic profiling of the drug. Copyright (C) 2001 John Wiley & Sons, Ltd.