DETERMINATION OF PHOSPHATE IN SAMPLES WITH HIGH-LEVELS OF SULFATE BY ION CHROMATOGRAPHY

A comparative study of the separation of phosphate from chloride, nitr ate, nitrite, bromide and sulphate by ion chromatography with direct c onductimetric detection and indirect photometric detection was perform ed. The best resolution was obtained using borate-gluconate or hydroge nphthalate as the eluent. Indirect photometry using hydrogenphthalate or naphthalenedisulphonate gave the best detection limit for phosphate (1 ng). The use of ion-exchange resins in the barium form for the eli mination of high levels of sulphate prior to the determination of trac e amounts of phosphate was evaluated. For the elimination of sulphate in samples containing less than 1000 mg/l (SO42-:PO43- = 100) the colu mn mode can be used, but for samples with high concentrations of sulph ate (5000 mg/l) the batch procedure is recommended. The behaviour of c ommercial cartridges in the barium form was also evaluated. The method was applied to the separation and determination of anions in saline s ediments.