Extraction-Spectrophotometric Determination of Benzethonium in the Presence of Quaternary Ammonium Salts with 2, 6-Dibromophenolindophenol

Abstract

Quaternary ammonium salts, amines and alkaloids are quantitatively extracted into organic solvents by forming respective ion pairs with a dye anion. These, however, interfere strongly with determination each other. For the enhancement of selectivity, various dye anions, such as 2, 6-dichlorophenolindophenol, picric acid and 2, 6-dibromophenolindophenol (DBIP) were examined against onium compounds. Of these dyes, DBIP was the most effective on the enhancement of sensitivity and selectivity in the determination of benzethonium. DBIP is a monoprotic acid, forming an ion-associate with benzethonium at pH5-10, which is effectively extracted into 1, 2-dichloroethane. Though other quaternary ammonium salts and amines were extractable at pH 8.2, their extractability was very poor at pH 5.6. Thus, only benzethonium could be determined spectrophotometrically at pH 5.6 without the disturbance of other quaternary ammonium salts and amines.
The extract had a maximum absorbance at 640 nm and the calibration curve obtained at pH 5.6 was linear over the range of (1 - 5) x 10^-6mol/l {0.448-2.24μg/ml} in aqueous solution with a good precision. The species was assumed to be [DBIPT]^-·[Benzethonium]⁺ from mole ratio method.