All reagents were obtained from Aldrich with the highest grade available and used without further purification. All solutions were prepared using deionised water from Vivendi UHQ grade water system (Vivendi) with a resistivity of not less than 18.2Mcm at room temperature. As(III) stock solution (5 mM ) waspreparedwithNaAsO2 dissolvedin0.1MaqueousHC