Fluorimetric determination of arsanilic acid by flow-injection analysis using on-line photo-oxidation

A flow-injection–fluorimetric method for the determination of arsanilic acid is proposed. The assay is based on the on-line decomposition of arsanilic acid in the presence of peroxydisulfate on irradiation with UV light. The arsenate generated in the photochemical reaction was reacted with molybdate in dilute nitric acid to form arsenomolybdic acid, which oxidised thiamine to thiochrome. The thiochrome was monitored fluorimetrically at 440 nm with excitation at 375 nm. The calibration graph was linear in the range 0.10–10.8 µg mL–1 with a correlation coefficient of 0.999. The detection limit was 0.01 µg mL–1 and the sample throughput was 55 samples h–1. The applicability of the method was demonstrated by determining arsanilic acid in animal foodstuffs and water.