Use of bromophenol blue in the spectrophotometric and turbidimetric determination of mebrophenhydramine in tablets

Simple, sensitive, rapid and cost-effective methods are described for the determination of mebrophenhydramine hydrochloride (MPH) in pure form and in tablets using Bromophenol Blue (BPB) as a reagent. The spectrophotometric method is based on the formation of an ion-association complex of the drug with BPB in phthalate buffer of pH 3.0, its extraction into chloroform and absorbance measurement at 420 nm. In turbidimetry BPB was used to produce stable turbidity arising from the formation of drug-dye complex of very low solubility at an altered pH condition and reagent-concentration and in the presence of potassium chloride. The absorbance of the turbid suspension was measured at 650 nm. Various parameters affecting the analytical procedures were investigated and optimised. In spectrophotometry, Beer's law is obeyed over the concentration range of 2-12 μg mL with an apparent molar absorptivity of 1.98×10 L moL cm and Sandell sensitivity of 19.39 ng cm. Turbidimetry is applicable in the concentration range of 10-70 μg mL. The limits of detection are 0.10 and 0.44 μg mL for spectrophotometry and turbidimetry, respectively. The methods were used to determine MPH in standard solution with a coefficient of variation of less than 2%, and were further applied to the determination of MPH in tablets. The results obtained by the proposed methods agree with the label claim. The reliability of the methods was further established by recovery studies applying standard-addition technique.