Sensitive Extractive Simpler Spectrophotometric Methods for the Microdetermination of Diltiazem HCl and Pipazethate HCl in Pure and Tablet Dosage Forms

Three new, rapid, sensitive, economical and simpler spectrophotometric methods (A-C) have been developed for the microdetermination of diltiazem hydrochloride (DT-HCl) and pipazethate hydrochloride (PZ-HCl) in pure and tablet dosage forms. In method A, simpler direct spectrophotometric measurements in ultra violet region have been developed for the determination of DT-HCl and PZ-HCl without any chemical reagents. A solution of DT-HCl or PZHCl in 0.1 M HCl shows maximum absorbance at 238 and 253 nm, respectively. After optimization, the systems obeyed Beer's law in the concentration range of 2-25 and 5-60 g/mL for DT-HCl and PZ-HCl, respectively. The apparent molar absorptivities were found to be 1.837 x 10⁴ and 7.931 x 10³ L mol^-1 cm^-1 for DT-HCl and PZ-HCl, respectively. Whereas the methods B and C involves the formation of intense yellow ion-association complex between drug(s) and either of phenol red (PR) or chlorophenol red (CPR) reagents followed by extraction with methylene chloride. The ion-associates exhibit absorption maxima at 390 and 402 nm for DT-HCl and at 393 and 405 nm for PZHCl with PR and CPR, respectively. After optimization, the systems obeyed Beer's law in the concentration range of 11.28-112.75 and 2.26-48.48 μg/mL for DT-HCl and 8.72-104.64 and 3.27-49.05 μg/mL for PZ-HCl with PR and CPR, respectively. The apparent molar absorptivities were found to be 4.086 x 10³ and 9.919 x 10³ L mol^-1 cm^-1 for DT-HCl and 4.212 x 10³ and 9.624 x 10³ L mol^-1 cm^-1 for PZ-HCl with PR and CPR, respectively. In methods A- C Sandell's Sensitivity, the slope, intercept, correlation coefficient, relative standard deviation (RSD), detection and quantitation limits were also calculated (n=5) for DT-HCl and PZ-HCl. No interference was observed from common excipients present in pharmaceutical formulations. The results are well compared to those obtained by the reference methods using t- and F-tests. Therefore, the present methods are suitable for the drugs determination, as they are sensitive and precise to a high extent.