Nitroprusside as a Novel Reagent for Flow Injection Spectrophotometric Determination of Captopril

A novel flow injection system for the determination of captopril in pharmaceutical formulations is described. Nitroprusside was employed as a new, nontoxic reagent. Captopril reacted with nitroprusside in basic solution to yield a red chromophore with maximum absorbance at 521nm. The calibration relationship was linear for concentrations from 3.0x10(-6) to 1.0x10(-3)molL(-1) with a limit of detection of 1.0x10(-6)molL(-1). The recoveries from captopril tablets were between 99.7 and 102.3%. The sampling frequency was 50h(-1) and the relative standard deviation was estimated to be 1.0% for 5.0x10(-4)molL(-1) captopril. A paired t-test showed that analysis of tablets by the flow procedure and a potentiometry provided similar results at the 95% confidence level.