Thin-Layer Radiochromatographic Determination of Captopril (SQ 14,225) and its Disulfide Dimer Metabolite in Blood

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Abstract
A reliable thin-layer radiochromatographic (TLRC) assay has been developed for quantitation of radiolabeled captopril (CP), a new sulfhydryl-containing orally active antihypertensive agent, and its disulfide dimer metabolite (CPD) in blood. CP, which is chemically unstable in blood, was immediately converted to a stable derivative by addition of N-ethylmaleimide (NEM) to freshly collected samples. Aliquots of whole blood samples were analyzed for total radioactivity, and NEM-treated aliquots were extracted with methanol. Reconstituted residues of the extracts were applied to silica gel GF plates, developed with chloroform/ethyl acetate/glacial acetic acid (4:5:3), and analyzed for radioactivity associated with CP and CPD by zonal analysis.