Determination of captopril in blood and urine by high-performance liquid chromatography.

Abstract
A new procedure was established for the determination of [the antihypertensive agent] captopril [1-(D-3-mercapto-2-methyl-1-oxopropyl)-L-proline] in biological fluids. Captopril was trapped with p-bromophenacyl bromide or N-(4-dimethylamino-3,5-dinitrophenyl)maleimide (DDPM), then the addition products were separated and determined by high-performance liquid chromatography (HPLC) on a reversed-phase column. The disulfides, metabolic products derived from captopril and excreted in the [human] urine, were reduced with tributylphosphine to captopril, which in turn was trapped with DDPM. These adducts were separated and determined by HPLC. The method provided quantitative results for captopril levels of 5-2000 ng/ml of whole blood and 0.1-100 .mu.g/ml of urine with satisfactory accuracy and percision.