Chromium speciation in environmental samples by solid- phase extraction using lewatit ionac SR-7 resin and flame...

A new method for the speciation, preconcentration, and separation of Cr(lll) and Cr(VI) species in different matrixes was developed using SPE combined with flame atomic absorption spectrometry. Theprocedure is based on the exchange of Cr(VI) ions as CrO(4)(2-) with CI- ions on Lewatit lonac SR-7 ion-exchange resin. After the oxidation of Cr(lll) to CrO(4)(2-) ions by concentrated H202 in basic medium, the procedure was applied to the determination of total Cr. Cr(lll) was calculated as the difference between the total Cr and Cr(VI) contents. The influence of the analytical parameters including the pH of the solution, amount of resin, eluent type, sample volume, and flow rates of the sample and eluent solutions were investigated. No considerable interferences were observed from: other anions and cations investigated in the Cr speciation. The preconcentration factor was found to be 500. The LOD for Cr(VI), corresponding to three times the SD of the blank, was 0.003 μg/L. The sorption capacity and binding equilibrium constant were calculated as 17.2 mg/g and 2.54 L/mg, respectively. The accuracy of the method was verified by analyzing certified reference materials. The proposed method was applied to the speciation of Cr species in real samples with satisfactory results.