The objective of the present work is to develop simple, precise and accurate colorimetric methods for the estimation of alverine citrate (ALV), tapentadol (TAP) using bromophenol blue (BPB) reagent. The method was developed on Perkin Elmer LAMBDA 25 UV –VIS spectrophotometer with 1cm quartz cells. The methods are based mainly on the formation of ion-pair complexes of the drugs with acidic dye; bromophenol blue followed by extraction into organic solvent. The colored complexes exhibited maximum absorbance measured at 423 nm for ALV, 416 nm for TAP, respectively. The linearity was assessed and found to be 20-100 μg/ml for ALV, 100-500 μg/ml for TAP, respectively. The colorimetric methods were extensively validated as per ICH guidelines and all the parameters were within the acceptance criteria with correlation of 0.9999. The accuracy and precision studies showed % RSD less than 2 for both the methods. The methods were proved to be more accurate, simple, precise and rapid by statistical validation, hence could be applied for regular analysis.
