Extractive spectrophotometric methods for determination of terbinafine hydrochloride in pharmaceutical formulations using some acidic triphenylmethane dyes

Three simple and sensitive extractive spectrophotometric methods have been described for the assay of terbinafine 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 show absorbance maxima at 410 nm for all three methods. Beer’s law is obeyed in the concentration ranges 2.0-25, 2.0-25 and 2.0-25 μg/mL with BTB, BPB and BCG respectively. The effects of concentration of dye, pH, and interference of excipients have been studied and optimized. The limits of detection and quantification have been determined for three methods. All the three methods have been validated as per the guidelines of ICH. The methods have been applied for the determination of drug in commercial tablets and the results of analysis are validated statistically through recovery studies.