SELECTIVE SPECTROPHOTOMETRIC DETERMINATION OF FENOTEROL BY THREE DIFFERENT METHODS.

Three simple and selective spectrophotometric methods were developed for the quantitative determination of Fenoterol in pure forms as well as in its pharmaceutical formulation. Method [A] Involves the coupling of the drug as phenolic compound with the diazonium salts of four amines, namely, Benzocaine (BZC), sulphadiazine (SDZ), sulphacetamide (SCM) and sulphanilic acid (SPA) forming red azodyes absorbed at 526, 514,  512 and 513 nm, respectively. Beer's law was obeyed in the concentration ranges of 10-70, 6-42, 4-28 and 3.5-24.5 μg ml^-1 for the four reagents, respectively. Method [B] is based on reaction of Fenoterol with cobalt thiocyanate, where by a sparingly soluble blue ion-pair complex is formed. This complex is extracted by toluene and spectrophotometrically measured at 619 nm. Good linearity was obtained in the range of   10-70  μg ml^-1. Method [C] is based on  the reduction of iron (III) by Fenoterol in acid medium and subsequent interaction of iron (II) with ferricyanide to form Prussian blue. The product exhibits absorption maximum at 730 nm. Beer's law was obeyed in the concentration range of 1.5–10.5 μg ml^-1. The reaction conditions for described methods were studied and optimized. The proposed methods were applied to the determination of Fenoterol in pharmaceutical formulation and the results demonstrate that the methods are equally accurate and precise as the reported methods found from the t and F values. The reliability of the methods was established by recovery studies using standard addition technique.