Spectrophotometric Determination of Lignocaine in Pure Form and in Pharmaceutical Preparations

Abstract

Two spectrophotometric methods have been developed for the determination of lignocaine in pure raw material or in formulated dosage form. One of these methods is based on the extraction of the ion-associate formed with reineckate salt by nitrobenzene or chloroform/acetone [solvent mixture, 1:1 (v/v)] and the absorbance is measured at 525 nm and at pH 5. Beer's law is obeyed in the range 0.2-2.0 mg/mL. The other method depends on the oxidation of lignocaine by Ce(IV), the excess of Ce(IV) is reacted with chromotrope 2B or chromotrope 2R where the red colour of the reagent decreases. The absorbance is measured at 510 and 530 nm and the methods are found useful in the concentration ranges 0.5-2.5 and 1.1-3.4 μg/mL, respectively. In another approach iron (II) is added to the excess Ce(IV) followed by the reaction with thiocyanate, salicylate or o-phenanthroline. The developed colours are measured at 450, 520 and 510 nm with concentration ranges 1.5-12.3, 1.8-10.6 and 0.5-4.3 μg/mL, respectively. It is evident that the use of the thiocyanate method is more preferable due to its wider usable concentration range.