On-line preconcentration using chelating and ion-exchange minicolumns for the speciation of chromium(iii) and chromium(vi) and their quantitative determination in natural waters by inductively coupled plasma mass spectrometry

Abstract

There are only a few analytical techniques available that have sufficient sensitivity and selectivity for the determination and speciation of chromium in environmental waters. In this work, a non-chromatographic system is developed for the simultaneous determination of chromium(III) and chromium(VI) by solid phase extraction and inductively coupled plasma mass spectrometry (ICP-MS). The system is based on the use of three minicolumns packed, respectively, with chelating and anionic ion exchange resins, which were placed in the injection valve of a simple flow manifold. By using this device, diverse advantages are attained: speciation and simultaneous determination of Cr(III) and Cr(VI) as well as increase of the sensitivity and reduction of the interferences by the preconcentration. The effects of chemicals and flow variables were investigated. Detection limits (2 min sample loading time) were 0.009 μg L⁻¹ for Cr(VI) and 0.03 μg L⁻¹ for Cr(III). The relative standard deviations (n = 10) for 0.3 μg L⁻¹ of Cr(VI) and Cr(III) were 3.2% and 2.6%, respectively, demonstrating a good precision for the analysis. The accuracy of the proposed method was checked with certified reference materials. Values obtained were in accordance with those reported for the certified materials. The method was applied to the determination of chromium species in different seawater samples.