Automated determination of total captopril in urine by liquid chromatography with post-column derivatization coupled to on-line solid phase extraction in a sequential injection manifold

► We developed a fully automated method for total captopril. ► Total captopril was determined in human urine. ► Sequential injection was coupled to liquid chromatography. ► Sample preparation was carried out on-line. ► Captopril was determined after post column derivatization. The present study reports a new liquid chromatographic (HPLC) method for the determination of the anti-hypertension drug captopril (CAP) in human urine. After its separation from the sample matrix in a reversed phase HPLC column, CAP reacts with the thiol-selective reagent ethyl-propiolate (EP) in a post-column configuration and the formed thioacrylate derivative is detected at 285nm. Automated 4-fold preconcentration of the analyte prior to analysis was achieved by an on-line solid phase extraction (SPE) step using a sequential injection (SI) manifold. The Oasis HLB SPE cartridges offered quantitative recoveries and effective sample cleaning by applying a simple SPE protocol. The limits of detection and quantitation were 10μgL−1 and 35μgL−1 respectively. The percent recoveries for the analysis of human urine samples ranged between 90 and 96% and 95 and 104% using aqueous and matrix matched calibration curves respectively.