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 in pharmaceutical formulations. The developed methods involve formation of coloured chloroform extractable ion-pair complexes of the drug with bromothymol blue (BTB), bromophenol blue (BPB) and bromocresol green (BCG) in acidic medium. The extracted complexes showed absorbance maxima at 415 nm for all three methods. Beer's law is obeyed in the concentration ranges 2.5-20.0, 2.5-10.0 and 2.5-12.5 microg ml(-1) with BTB, BPB and BCG, respectively. The methods have been applied to the determination of drug in commercial tablets and capsules. Results of analysis were validated statistically and through recovery studies.