Main content area

The use of stable isotopes for Cr(VI) determination in silty-clay soil solution

Zuliani, Tea, Ščančar, Janez, Milačič, Radmila
Analytical and bioanalytical chemistry 2013 v.405 no.23 pp. 7231-7240
buffers, chromium, environmental hazards, groundwater, high performance liquid chromatography, isotope dilution technique, mass spectrometry, pH, soil, soil sampling, soil solution, stable isotopes, tannery waste
In assessing the environmental hazard of Cr(VI) present in soil, exchangeable Cr(VI) is important, since it can be easily washed out from the upper part of the soil into subsurface soil, surface and ground water, and taken up by plants. The aim of this study was to evaluate the degree of species interconversion that may occur during the extraction of exchangeable Cr(VI) from silty-clay soil with phosphate buffer in order to establish an extraction method that would be effective, accurate and with minimal or no species interconversions. The Cr(VI) concentration in soil extracts was determined by speciated isotope dilution inductively coupled plasma mass spectrometry (SID-ICP-MS). The study was performed on soil samples from a field treated with tannery waste for 17 years. Samples were spiked by enriched stable isotopic solutions of⁵⁰Cr(VI) and⁵³Cr(III) that were added to phosphate buffers (0.1 M KH₂PO₄-K₂HPO₄(pH 7.2) and/or 0.1 M K₂HPO₄(pH 8)). To optimize extraction, mechanical shaking and/or ultrasound-assisted extraction were compared. The separation and detection of Cr species was performed by high-performance liquid chromatography (HPLC) ICP-MS. When mechanical shaking was applied, 90 % reduction of Cr(VI) was induced by extraction with 0.1 M KH₂PO₄-K₂HPO₄, while with 0.1 M K₂HPO₄reduction was around 40 %. To shorten the extraction time and the possibility of species interconversions, ultrasound-assisted extraction was further applied only with 0.1 M K₂HPO₄. For total extraction of exchangeable Cr(VI) with a maximum 10 % reduction of Cr(VI), five consecutive ultrasound-assisted extractions were needed.