Determination of total captopril in dog plasma by HPLC after prelabelling with ammonium 7-fluorobenzo-2-oxa-1,3-diazole-4-sulphonate (SBD-F).

Abstract A HPLC method has been developed for the determination of captopril, an angiotensin-converting enzyme (ACE) inhibitor, in dog plasma. The plasma was deproteinized with trichloroacetic acid (TCA) containing N-(3-mercapto-1-oxopropyl)-piperidine-2-carboxylic acid SQ 25,233 as an internal standard, adjusted to pH 9.5 with borate buffer containing tri- n -butyl phosphine (TBP) to reduce the oxidized captopril, and treated with a thiol specific reagent, SBD-F. The fluorescent derivatives of captopril and the internal standard were separated from other interfering peaks on a reversed-phase column and determined by HPLC. The proposed method was simple, selective and sensitive. The total plasma concentration of captopril reached a maximum of 3.04 ± 0.54 μg/ml (mean ± S.E.) 60 min after administration of the drug.