Rapid leaching of Cr(VI) in soil with Na3PO4 in the determination of hexavalent chromium by electrothermal atomic absorption spectrometry

A method has been developed that leaches Cr(VI) selectively from soil samples. Hexavalent chromium was leached completely from soil with 0.01 mol L−1 Na3PO4. This was achieved by boiling the soil–reagent solution mixture for a period of 5 min. The leached Cr(VI) was then quantified by electrothermal atomic absorption spectrometry (ET-AAS) after filtration of the sample solutions through Hydrophilic Millipore PVDF 0.45 μm filter.Statistical evaluations indicated that the new developed method is reliable since neither its comparison with the established method nor the comparison of the sum of the concentrations of chromium species to that of the total concentration of chromium show any difference at 95% level of confidence. The spiking of soil samples with Cr(III) standards before pretreatment show that Cr(III) was not oxidized to Cr(VI) during leaching as the Cr(VI) content never increased. The detection limit established was 0.07 μg g−1, which is an improvement to that of the US EPA method 3060A by a factor of more than 500.The maximum concentrations of Cr(VI) found in soil samples collected around the new chromium mine was 8.0 μg g−1 and falls within acceptable level of 15 μg g−1 in accordance with the Italian Guidelines.