Ion Chromatography of Soluble Cr(III) and Cr(VI)

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Abstract
Ion chromatography coupled with a conductivity detector was used for the analysis of soluble Cr(III) and Cr(VI) in aquatic samples. An IC methodology for Cr(III) was developed and tested for a period of one year. The method involves the use of a low capacity cation column and an eluent containing tartaric acid, ethylenediamine, and acetonitrile at a pH of 2.9. At a k′ of 10.61, a lower detection limit of 0.2 mg/L can be achieved with less than 5% coefficient of variation. No statistical differences were detected when the method was compared with the AA method in different water matrices spiked with Cr(III). Column deterioration and instability of the standard Cr(III) can be eliminated by regeneration of the column with 50 mL of 10 mM HNO3 and by daily preparation of the standard. The mobile phase is the most suitable sample solvent. A low capacity anion column can be used to analyze Cr(III) as a complex anion with EDTA at pH 5.0 at a detection limit of 1 mg/L. The anion column was also useful for Cr(VI) analysis. The best results were obtained with eluent containing sodium gluconate, boric acid, sodium tetraborate, glycerin, and acetonitrile at pH 9.2. The calibration curve was linear between 1.0 and 100 mg/L.