DETERMINATION OF THE ANGIOTENSIN-CONVERTING ENZYME-INHIBITOR LISINOPRIL IN URINE USING SOLID-PHASE EXTRACTION AND REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A simple, accurate and precise high-performance liquid chromatographic method is described for assaying lisinopril in human urine. Urine (1 mi) containing lisinopril and enalaprilat (internal standard) was acidified with 10 mu l of 6 M nitric acid, passed through a Sep-Pak C-18 cartridge and eluted with 3 mi of 10% acetonitrile, followed by 6 mi of distilled water. The separations were carried out using a mu Bondapak C-18 column with a mobile phase comprising acetonitrile (60 ml), methanol (10 ml) and tetrahydrofuran (10 ml) in 15 mM phosphate buffer (920 mi) at pH 2.90. Separations were performed at 40 degrees C and detection was at 206 nm. Standard calibration plots of lisinopril in urine were linear (r > 0.998) and recovery was greater than 64%. The lowest quantifiable concentration was 0.5 mu g/ml. Within-day and between-day imprecision (coefficient of variation) ranged from 2.51% to 9.26%, and inaccuracy was less than 8.3%.