Spectrophotometric Determination of Sulfate Ion Through Copper(II)-azide System

An indirect and alternative method for the determination of sulfate ion has been established by spectrophotometry. The procedure is based on the formation of copper(II) monoazido species, in water/acetone medium, in which a discoloration effect of system is caused by sulfate presence. In the recommended conditions, sulfate ions can be determined in the concentration range from 40 to 5000 mg/l (ppm), at 375 nm, in natural samples of waters. The best experimental conditions were determined analysing the different factors involved. Studies about the formation equilibria of the CuN 3 + and CuSO 4 species were realized in water and their respective stability constants (β 1 = 225 M −1 and 7.15 M −1 ) were determined by spectrophotometry at 25.0° C and ionic strength 1.0 M (NaClO 4 ). Equilibrium investigations were also made in presence of acetone. Additional studies on the ternary system Cu(II)/N 3 − /SO 4 2- ) indicated some evidences of mixed complexes.