Original Articles
K. Vijaya Raju, N. Annapurna,
Abstract
A Simple, convenient and accurate spectrophotometric titration and a visual end - point method [employing a redox indicator] have been developed for the determination of Labetalol[LBT], a premier B.P drug (Molecular Formula: C19H24N2O3 HCl. Molecular Weight 364.87), using hexacyanoferrate(III) [HCF(III)] as an oxidizing agent for the first time. The spectrophotometric method consists of titrating the drug solution in about 4M alkaline medium (sodium hydroxide) using a standard solution of hexacyanoferrate(III) at 420nm. In the case of visual end - point method, however, the drug solution in about 4M sodium hydroxide medium, is treated with a known excess of HCF(III) solution and the excess HCF(III) is titrated against a standard solution of iron(II) solution in phosphoric acid medium [about 9M] and in presence of zinc sulphate using diphenylamine as a redox indicator. The drug labetalol in the range 0.32mg – 0.97mg (by spectrophotometric method) and in the range of 0.63mg – 1.89mg (by visual end - point method) have been determined with an accuracy of ± 0.7% and ± 0.8% respectively. The precision of both the methods have been assessed by computing pooled standard deviation and 95% confidence limits. In these methods the drug is oxidized by HCF(III) in a two electron oxidation step. The oxidation products of the drug have been identified and confirmed by IR-spectrum. The advantages of the present methods over the earlier ones have been discussed.