Rapid method for the spectrophotometric determination of sulphate in surface water using ion-exchange separation and the sulphate and chlorophosphonazo III (CPA III)-Ba2+ complex reaction

A rapid spectrophotometric method for the determination of SO 4 2− in surface water is reported. It is based on the reaction of CPA III-Ba2+ complex with SO 4 2− in acidic medium in the presence of ethanol. Beer's law is obeyed up to 120 Μg of SO 4 2− in 25 ml solution. The molar absorptivity is 6.3×103 l · mol−1 · cm−1 at 500 nm, and the coefficient of variation varies from 1.85% to 3.10%. The absorbance remains stable for at least 24 h and interfering ions are separated by strongly acidic cation-exchange resin.