Reversed flow-injection manifold for the spectrophotometric determination of captopril based on its inhibitory effect on the Co(II)–2,2′-dipyridyl-2-pyridylhydrazone complex formation

The present work reports a new, simple and rapid reversed flow-injection (r-FI) method for the accurate and precise spectrophotometric determination of captopril (CPL) in pharmaceutical formulations. The method is based on the inhibitory effect of CPL on the complex formation of Co(II) with 2,2′-dipyridyl-2-pyridylhydrazone (DPPH). The chemical and FI variables were studied and optimized. The calibration graph was linear in the range 0–250 mg l−1 CPL, at a sampling rate of 60 injections per hour. The method was found to be very precise [sr=0.8% at 100.0 mg l−1 CPL (n=12)] and the 3σ detection limit (cL=2.5 mg l−1) was quite satisfactory. Its application to commercially available pharmaceuticals produced excellent results, with a mean relative error of er<1.0%.