Spectrophotometric determination of lansoprazole in pure and pharmaceutical forms using triphenyl methane dyes

Four simple and sensitive extractive spectrophotometric methods have been described for the assay of Lansoprazole 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), bromocresol purple (BCP) and bromocresol green (BCG) in acidic medium. The extracted complexes showed absorbance maxima at 419, 417, 416 and 414nm with use of the cited reagents, respectively. The stoichiometry of the complex is found to be 1:1 in each case. Beer’s law is obeyed in the concentration ranges 2.5-25, 4.0-30, 4.0-40 and 4.5-45μg/ml with BTB, BPB, BCP and BCG respectively. The effect of concentration of dye, pH, and interference of excipients have been studied and optimized. The limits of detection and quantification have been determined for four methods. All the four 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.