Fluorimetric determination of quinones with 3-aminothiocarbostyril

Fluorimetric analysis with 3-aminothiocarbostyril. I

Abstract

A selective fluorimetric method for the determination of p-benzoquinone(BQ) and 1, 4-naphthoquinone(NQ) with 3-aminothiocarbostyril (ATC) was developed on the basis of the fact that characteristic fluorescence was formed by the reaction of ATC with BQ and with NQ, but no fluorescence with o-benzoquinone and with 1, 2-naphthoquinone. (1) BQ reacts with ATC in a dilute sulfuric acid solution in the presence of a small amount of hydrogen peroxide. The reaction product developes, in an alkaline solution, a yellow green fluorescence which has the excitation maximum at 394 nm and the emission maximum at 530 nm. Fluorescence is linear over the range (0.55.0) μg ml^-1. The coefficient of variation is 0.6% (n=10) for 3.0 μg ml^-1 of BQ. The recommended procedure is as follows: To 5.0 ml of the test solution are added 2 ml of 60% (w/v) sulfuric acid, 0.1 ml of 0.15% hydrogen peroxide solution, and 0.25 ml of 0.1% ethanolic solution of ATC. The mixture is heated in a glass-stoppered test tube for 30 min in a boiling water bath and cooled to room temperature. The reaction mixture is neutralized with 10% sodium hydroxide, adjusted to pH 12 by the addition of 10 ml of 0.5 M NaOH-0.5 M Na₂HPO₄ buffer solution, diluted with water to 50.0 ml. The fluorescence intensity of the solution is measured at 530 nm with excitation at 394 nm. (2) NQ reacts with ATC in a dilute sulfuric acid solution. The reaction product developes, in a chloroform solution, a red fluorescence which has excitation maxima at 534 and 564 nm and emission maximum at 610 nm. Fluorescence is linear over the range (0.010.5) μg ml^-1. The coefficient of variation is 1.8% (n=10) for 0.2μg ml^-1 of NQ. The recommended procedure is as follows : To 5.0 ml of the test solution are added 2 ml of 5% (w/v) sulfuric acid and 2 ml of 0.2% ethanolic solution of ATC. The mixture is heated for 90 min at 75°C, and cooled to room temperature. Ten ml of 10% sodium hydroxide solution is added to the solution and extracted with three 5-ml portions of chloroform. The chloroform layers are combined and diluted with chloroform to 20.0 ml. The fluorescence intensity of the solution is measured at 610 nm with excitation at 564 nm.