AN IMPROVED SOLID-PHASE EXTRACTION PROCEDURE FOR THE DETERMINATION OF ANTIDEPRESSANTS IN SERUM BY COLUMN LIQUID-CHROMATOGRAPHY

A convenient and economical procedure for the isolation of antidepressant drugs from serum is described. A 0.7 mL aliquot of the sample after the addition of trimipramine or protriptyline as the internal standard is vortex mixed with 0.7 mL of acetonitrile and centrifuged. The supernatant is applied to 1-mL BondElut C-18 silica extraction column which has been conditioned by subsequent washing with 1 M HCl, methanol, water, and 1% potassium bicarbonate solution. After passing the sample at a slow rate, the column is washed twice with water and once with acetonitrile. The desired compounds are then eluted with a 0.25 mL aliquot of a mixture of 35% perchloric acid and methanol (1:20). A 50-muL aliquot of the eluate is injected onto a 15 cm x 4.6 mm (i.d.) column packed with 5-mum C-8 silica particles, which is eluted at ambient temperature with a mobile phase containing tetramethylammoniun perchlorate and acetonitrile. The peaks are detected with an absorbance detector at 215 nm or 226 nm for fluoxetines. The resulting chromatogram shows only a few extraneous peaks. The extraction recovery of the commonly prescribed antidepressants is in the range of 90% allowing their quantitation at a level of 5 ng/mL.