Spectrofluorimetric determination of arsenic in water samples

Parts per billion (ppb) levels of arsenic can be determined by using the fluorimetric method described here. It is based on the formation of an anionic complex of arsenic(V) with benzene-1,2-diol (catechol) and subsequent formation of an ion-association complex with 3,6-bis(dimethylamino)acridine, known as acridine orange. This was extracted quantitatively in toluene. The dye is then back-extracted with acid in the aqueous layer. In a basic medium it shows a bright yellow fluorescence at a λem of 530 nm (λex, 480 nm). The fluorescence intensity is a direct measure of the arsenic(V) concentration. The calibration graph is linear in the range 4–400 ppb. Arsenic(III) was also quantified following oxidation. The method is not interfered with by phosphate. It is applicable to real samples.