Speciation of bio-available chromium in soils by solid-phase extraction and graphite furnace atomic absorption spectrometry

Speciation of bio-available chromium in soils was performed using extraction with 0.05 M EDTA followed by strong anionic solid-phase extraction. The step gradient elution technique with 0.1 and 0.5 M NaCl as eluent in sequence was sufficient to separate Cr(III) and Cr(VI) with recoveries of 99.7 and 93.4%, respectively. During the determination of separated chromium species by graphite furnace atomic absorption spectrometry (GFAAS), 10% ammonium nitrate solution was co-injected with the sample to eliminate the interferences from the eluent matrix containing high concentrations of chloride. Linear calibration curves over the range of 0-15 ng mL−1 were obtained with good correlation coefficients (R2 = 0.9976 for Cr(III)EDTA−, and 0.9897 for Cr(VI)). The sum of the chromium species determined after separation was in good agreement with total chromium from EDTA extraction of NIST soil standard SRM2709 (0.688 μg g−1 Cr(III), 0.127 μg g−1 Cr(VI), 0.742 μg g−1 total Cr) and a local soil sample (0.030 μg g−1 Cr(III), 0 μg g−1 Cr(VI), 0.053 μg g−1 total Cr).