SPECTROPHOTOMETRIC DETERMINATION OF SOME LOCAL-ANAESTHETICS BY USING PICRYL-CHLORIDE AND CHLORANILIC ACID

Abstract

Two simple and sensitive spectrophotometric methods are described for the determination of ten local anaesthetics. The first one was based on measuring of coloured products resulting from using picryl chloride as a derivatlzaiion reagent for the quantification of the drugs. The cited reagent reacts with the amino group of local anaesthetic in acetone using anhydrous potassium carbonate as hydrochloride acceptor. The reaction was completed within 2 minutes on hot water-bath at 6(1°. The coloured products are quantified spectrophotometrically and exhibit two main absorption bands (370-375 nm) and (410-450 nm). The position of x._ differ according to the structure of the drug. The second method was based on the interaction of the drug and p-chloranillc acid to yield stable and intensively coloured ion-pair salt. The reddish violet chromogen formed was measured at 525 nm. Beer's law was obeyed in range form 2.5- 20 µ.glmlfor the first method and from 10-100 µglmlfor the second one. The optimization of the different experimental conditions is described. Applications of the suggested methods to representative pharmaceutical dosage forms are presented and compared with official methods with good accuracy and precision. The recoveries ranged from 98±1 to 100±0.6. Interferences from the commonly present additives or agents in pharmaceutical formulations were investigated. The proposed methods were found rapid and selective. The selectivity and specificity of plcryl-chloride method is exhibited by the different position of maximum wavelength and can differentiate between the investigated drugs.