Differential derivative spectrophotometric determination of phenobarbitone and phenytoin sodium in combined tablet preparations

A pH-induced differential derivative spectrophotometric procedure has been developed for the simultaneous determination of Phenobarbitone (PBT) and Phenytoin sodium (DPH Na) in tablet preparations. The method comprized of measurement of difference absorptivities derivatized in second order (DeltaD(2)) of a tablet extract in 0.01 N NaOH relative to that of an equimolar solution in 0.01 N HCl at wavelengths of 244.8 and 252.8 nm respectively. The presence of identical zero-crossing points for pure drug and tablet extract solutions established the non-interference of the excipients in the absorption at these wavelengths. The compliance of Beer's law was adhered over a concentration range of 7.5-25 mug ml(-1) for both PBT and DPH.