Determination of phosphate in samples with high levels of sulphate by ion chromatography

Abstract

A comparative study of the separation of phosphate from chloride, nitrate, nitrite, bromide and sulphate by ion chromatography with direct conductimetric detection and indirect photometric detection was performed. The best resolution was obtained using borate-gluconate or hydrogenphthalate 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 elimination of high levels of sulphate prior to the determination of trace amounts of phosphate was evaluated. For the elimination of sulphate in samples containing less than 1000 mg/l (SO 4 2−:PO 4 3− = 100) the column mode can be used, but for samples with high concentrations of sulphate (5000 mg/l) the batch procedure is recommended. The behaviour of commercial cartridges in the barium form was also evaluated. The method was applied to the separation and determination of anions in saline sediments.