SPECTROPHOTOMETRIC DETERMINATION OF SULFATE ION THROUGH COPPER(II)-AZIDE SYSTEM

An indirect and alternative method for the determination of sulfate io n has been established by spectrophotometry. The procedure is based on the formation of copper(II) monoazido species, in water/acetone mediu m, in which a discoloration effect of system is caused by sulfate pres ence. In the recommended conditions, sulfate ions can be determined in the concentration range from 40 to 5000 mg/l (ppm), at 375 nm, in nat ural samples of waters. The best experimental conditions were determin ed analysing the different factors involved. Studies about the formati on equilibria of the CuN3+ and CuSO4 species were realized in water an d their respective stability constants (beta1 = 225 M-1 and 7.15 M-1) were determined by spectrophotometry at 25.0-degrees-C and ionic stren gth 1.0 M (NaClO4). Equilibrium investigations were also made in prese nce of acetone. Additional studies on the ternary system Cu(II)/N3-/SO 42-) indicated some evidences of mixed complexes.