A stability-indicating spectrophotometric method for the determination of fenoterol in prarmaceutical preparations

A simple and highly sensitive spectrophotometric method was developed for t he determination of fenoterol hydrobromide in pharmaceutical formulations. The method is based on measurement of the orange-yellow color peaking at 43 6 nm, produced when the drug is coupled with diazotized benzocaine in triet hylamine medium. The method is applicable over the range of 0.5 - 10 mu g/m l, with minimum detectability of 3.6 ng/ml (approximate to 9.4 x 10(-9) M). The molar absorptivity is 4.61x10(4) L. mol(-1).cm(-1). with relative stan dard error of 0.196 %. The proposed method was successfully applied to the determination of fenoterol in its dosage forms; the mean recoveries of 99.6 1 +/- 1.59 and 98.97 +/- 1.52 for tablets and aerosols, respectively, were obtained. The results of the proposed method were favorably compared to tho se obtained by the official and reference methods. No interference was enco untered from the co-formulated drug ipratropium bromide, common excipients and alkaline induced degradation product. A proposal of the reaction pathwa y is presented.