CARBONIC ANHYDRASE-IMMOBILIZED PRECOLUMN FOR SELECTIVE ONLINE SAMPLE PRETREATMENT IN HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC DETERMINATION OF CERTAIN SULFONAMIDE DRUGS

Carbonic anhydrase (CA)-immobilized aminopropyl silica precolumn was d eveloped for direct injection determination of certain sulphonamide dr ugs in biological fluids by column-switching (CS) high-performance liq uid chromatography. Under the optimized conditions, only the sulphonam ide drugs with an unsubstituted sulphonamide group were retained on th e CA precolumn and separated on a reversed-phase analytical column. Of these, the retention of hydrochlorothiazide (HCT), chlorothiazide, ac etazolamide, furosemide (FS) and chlorthalidone was almost quantitativ e. The peak area of HCT was proportional to the concentration in the r ange of 1-100 nmol/mL with relative standard deviations of 3.7% (5 nmo l/mL) and 0.7% (100 nmol/mL). This CS system was applied to urine and plasma samples spiked with HCT and FS. Endogenous components of these were effectively removed, and HCT and FS were selectively retained on the CA precolumn. Almost quantitative recoveries and reproducibility w ere obtained.