An Evolved GFAAS Method for Trace and Ultratrace Determination of Cr(III) and Cr(VI) in Water and Wastewater: Speciation of Chromium

A highly evolved method for the determination of Cr(III) and Cr(VI) at the ppm to ppb level in water and wastewater samples has been developed. For the ppm level determination of chromium, Cr(III) is separated from Cr(VI) by its R2O3 precipitation along with Fe(OH)(3), then both Cr(III) and Cr(VI) are separately determined by GFAAS in a smaller aliquot of sample solution after removal of associated interfering elements by a novel solvent extraction system involving 2,Adihydroxynaphthalene as an extractant. However, for ppb level determination of Gr(III) and Cr(I), a pre-concentration technique needs to be combined with a solvent extraction system. Here, Cr(III) is separated and preconcentrated by R2O3 precipitation as above, however, from a large volume of water sample, i.e., about 400-500 mL. The analyte Cr(III) is further separated from iron and other interfering elements by selective solvent extraction using the same extractant (2,3-dihydroxynaphthalene) and was then determined selectively by GFAAS. Total chromium [Cr(III)+Cr(VI)] from a 400.500 mL separate water sample is preconcentrated as R2O3 ppt of Cr(III) [after reducing Cr(VI) with Rap] along with R2O3 ppt of Fe(III) generated in situ by way of oxidation of residual Fe(H) by HNO: t . Iron and other interfering elements are similarly removed by solvent extraction using the same extractant (2,34I,ND) as in the determination of Cr(III), and total Cr as Cr(III) is similarly determined by GFAAS. The content of Cr(VI) was deduced by subtracting the value of Cr(III) from the content of total chromium determined as Cr(III). The method developed is highly effective and reliable. While the detection limit (36) and %RSD of the method for ppm level chromium (without further preconcentration) was 0.4 mu g L-1 and 5-10%, respectively, at the 4.0 mu g L-1 level, the corresponding values of the method for ppb to ppt level chromium determination were 0.01 mu g L-1 and 3 to 5%, respectively, at the 0.1 mu g level. The pre-concentration factor of this system was similar to 40-50. The method was applied to a range of real samples and the results obtained have been successfully validated by standard methods.