Extractive spectrophotometric methods for determination of diltiazem HCl in pharmaceutical formulations using bromothymol blue, bromophenol blue and bromocresol green

Three simple and sensitive extractive spectrophotometric methods have been described for the assay of diltiazem hydrochloride either in pure form or i n pharmaceutical formulations. The developed methods involve formation of c oloured chloroform extractable ion-pair complexes of the drug with bromothy mol blue (BTB), bromophenol blue (BPB) and bromocresol green (BCG) in acidi c medium. The extracted complexes showed absorbance maxima at 415 nm for al l three methods. Beer's law is obeyed in the concentration ranges 2.5-20.0, 2.5-10.0 and 2.5-12.5 mug ml(-1) with BTB, BPB and BCG, respectively. The methods have been applied to the determination of drug in commercial tablet s and capsules. Results of analysis were validated statistically and throug h recovery studies. (C) 2000 Elsevier Science B.V. All rights reserved.