Sequential injection analysis of captopril based on colorimetric and potentiometric detection

The development of an analytical procedure based on the sequential injection analysis (SIA) concept for the analytical control of captopril in pharmaceutical formulations is described. The robustness of the proposed system is established by accuracy assessment that consists in yielding a versatile manifold for the carryout of two quasi-independent analytical determinations. One of the captopril determination procedures is based on the colorimetric measurement of the captopril-palladium complex in acid media at the 400nm. No interference from other compounds usually contained in the samples was found, even when its concentration was 25 times higher than that of the analyte. The other procedure involves the potentiometric titration of captopril with a 10-3mol/l Ag(I) solution used as titrant and the application of the Granʹs method for ascertaining the equivalence point. Accuracy of the proposed approach was attained by developing an in-line calibration procedure for the assessment of the electrode slope and performing titration in four different titrant/analyte mixtures. Precision of the developed procedures was better than 1.3%, being similar to that of the reference chromatographic method. The results attained were statistically similar to those given by the reference method and, thus, the accuracy assessment concept may be used for the determination of failures of the analytical procedure when performing large-scale analysis.