Extractive Spectrophotometric Methods for Determination of Sibutramine Hydrochloride using Acidic Triphenylmethane Dyes

Three simple and sensitive extractive spectrophotometric methods have been described for the assay of sibutramine 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 2.0-25, 2.0-20 and 2.5-25 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 to the determination of drug in commercial tablets and results of analysis were validated statistically through recovery studies.