COLUMN LIQUID-CHROMATOGRAPHIC DETERMINATION OF PAROXETINE IN HUMAN SERUM USING SOLID-PHASE EXTRACTION

A 0.5-ml aliquot of a serum sample, after the addition of a 100-mu l a liquot of a 5 mu g/ml solution of dibucaine as the internal standard, is vortex-mixed with 0.5 ml of acetonitrile and centrifuged. The super natant is applied to a 1-ml BondElut C-18 silica extraction column con ditioned with subsequent washings with 1 M HCl, methanol and water. Af ter passing the sample at a slow rate, the column is washed twice with water and once with acetonitrile. The desired compounds are then elut ed with a 0.25-ml aliquot of 35% perchloric acid-methanol (1:40, v/v). A 7-mu l aliquot of the eluate is injected onto a 150 x 4.6 mm I.D. c olumn packed with 5-mu m C-8 silica particles and eluted at ambient te mperature with a mobile phase of 10 mM phosphate buffer-acetonitrile ( 2:1, v/v) (pH 3.2). The peaks are detected with a fluorescence detecto r (excitation at 295 nm, emission at 365 nm). The resulting chromatogr am is clean with no extraneous peaks. Paroxetine and dibucaine give sh arp peaks which are well separated from each other and from the solven t peaks. The extraction recovery of the drug and the internal standard is in the range of 90% which allows a highly sensitive determination of paroxetine.