Fluorophotometric Determination of Trace Amounts of Arsenic(Ⅲ) in Water by Its Fluorescence Quenching Action

Trace amounts of arsenic(Ⅲ) was separated and enriched on sulfhydryl cotton from the sample solution acidified to 1 mol·L-1 with HCl,desorbed from the sulfhydryl cotton with conc. HCl and determined by fluorophotometry at wavelengths of (λex) 296 nm and (λem) 396 nm. In an ammoniacal buffer solution of pH 9.0,arsenic(Ⅲ) was reacted with the reagent 7-(2,4-dihydroxy-5-carboxyphenylazo)-8-hydroxyquinoline-5-sulfonic acid (DHCPAQS),leading to quenching of fluorescence of the reagent. Linear relationship between the magnitude of decrease in fluorescence intensity and concentration of arsenic(Ⅲ) was kept in the range of 0.5-6.0 μg·L-1 with detection limit (3S/N) of 0.2 μg·L-1. The proposed method was applied to determination of arsenic in samples of tap water,rain water and channel water,giving values of RSD′s (n=10) less than 3% and values of average recovery in the range of 102%-108%.