Ion chromatographic determination of borate in aqueous samples together with other common anions

Abstract

The conversion of boric acid (pK_a ≈ 9) in a more acidic complex, using mannitol or sorbitol as ligands, has been exploited to obtain a sensitive and accurate method for the determination of boric acid by ion chromatography. Both separation and detection conditions have been selected on the basis of available thermodynamic data on the relevant equilibria, and then experimentally optimised on a conventional ion cromatograph equipped with a suppressed conductivity detector. The performances of the method are practically identical for the two eluent solutions adopted, containing mannitol or sorbitol: the detection limit is about 1 µmol dm^–3, the linear response range extends up to 200 µmol dm^–3, the repeatability is better than 5% and the analysis time is less than 6 min. Moreover, other common anions (i.e., acetate, fluoride, and chloride) can be determined together with borate. The comparison of results with those obtained by conventional analytical techniques applied to real samples at known concentration of borate allows the estimation of a negligible bias for the ion chromatographic method.