Spectrofluorometric determination of captopril plus captopril disulfide metabolites in plasma.

Captopril disulfides and the drug covalently bound to proteins were reduced with tri-n-butylphosphine. After sample purification on an XAD-2 column, captopril was treated with 1-(7-dimethylamino)-4-methyl-2-oxo-2H -1-benzopyran-3-yl)-1H-pyrrole-2,5-dione to form a fluorescent derivative. After acidification, the fluorescent derivative was extracted into toluene and purified on a C18 cartridge. The fluorescence of the dimethyl-formamide eluate was measured at an excitation wavelength of 380 nm and a fluorescence wavelength of 440 nm.