Spectrophotometric determination of arsenic (V) with Bismuthiol II

Abstract

Arsenic(V) reacts with Bismuthiol II to form a light yellow precipitate in hydrochloric acid solution, which is extracted into chloroform. The spectrophotometric determination of As(V) based on this reaction was studied. The recommended procedure is as follows: To a sample solution containing up to 50 μg of As (V), hydrochloric acid and 5 ml of 0.1% reagent solution are added, the whole volume being adjusted to about 30 ml and the HCl concentration to (34) M. The solution is allowed to stand for 10 min at a temperature below 22°C. Then, the precipitate is extracted by shaking for 10 min with 10 ml of chloroform. To remove the excess reagent from the chloroform extract, it is washed twice by shaking for 90 s with 20 ml each of the buffer solution (potassium phosphate/sodium borate, pH 7.5) and the absorbance is measured at 335 nm against the reagent blank. Beer's law was held up to 50 μg-As(V) in 10 ml of chloroform and the molar absorptivity was 1.62×10⁴ l mol^-1 cm^-1 at 335 nm. Large amounts of Al (III), Cd(II), Co(II), Mn(II), Ni(II), Pb(II), Zn(II) and PO₄^3- do not interfere with the determination of As (V), but Cr(VI), Mo(VI), Pt(IV), Se(IV), Te(IV) and V(V) interfere.