A simple and inexpensive method for chromium speciation in soil extracts
Prokisch, J. | Kovacs, B. | Gyori, Z. | Loch, J.
Chromium (Cr) appears in two stable forms in nature as Cr(III) and Cr(VI). Hexavalent chromium (CrO4(2-); Cr2O7(2-)) is very toxic and carcinogenic, while inorganic Cr(III), however, is essential for mammals. Only two methods, atomic absorption and inductively coupled plasma atomic emission (ICP) spectrometry, provide information on the total amount of Cr in a test solution. This is the reason that several efforts have been made with regard to Cr speciation. Either an acidic or a basic activated aluminum oxide and a reversed phase C-18 column or an ion exchanger column are used for the separation of chromium(III) from chromium(VI) in FIA and HPLC analyses. In our experiments, acidic-activated aluminum oxide was used for separation. This alumina was placed into a silicon tube and connected to an ICP spectrometer between the nebulizer and peristaltic pump. The average grain size of the alumina was large enough that the solution could be pumped through the micro column. Acidic-activated aluminum oxide in the 2.0 to 8.0 pH range adsorbs the chromate anion but not the Cr(III) cation. During this stage, the Cr(III) content of a sample is measurable. The adsorbed chromate can be eluted with a strong acid. The height or area of the elusion peak can be used for the calibration of Cr(VI). Detection limits of 4 microgram/kg and 0.5 microgram/kg were obtained for Cr(III) and Cr(VI), respectively. The effects of sulphate and phosphate anions on the surface of the alumina on chromate adsorption were also evaluated. This method was used for the measurement of Cr(VI) concentration by 0.01M CaCl2 extraction of soil.
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