Determination of captopril and its disulphide in biological fluids.

A gas chromatographic-mass spectrometric method for the simultaneous determination of captopril (SQ 14,255) and its disulphide (SQ 14,551) in biological fluids by means of selected ion monitoring is described. In order to prevent oxidative degradation, captopril was treated with N-ethylmaleimide (NEM). The captopril-NEM adduct and the disulphide were converted into the hexafluoroisopropyl esters, which were separated on a 10% Dexsil 300 GC column and determined by employing the captopril-N-butylmaleimide adducts as an internal standard. The blood and urine levels of captopril and its disulphide in dogs to which captopril had been administered orally were measured by the proposed method. The urinary excretion of these two substances in rats was also determined in a similar manner.