Speciation of Cr(III) and Cr(VI) in the Presence of Chromium Azo Dye Acid Yellow 99 by Column Solid Phase Extraction

A novel method, which determines the concentrations of speciated Cr(III) and Cr(VI) with the presence of Cr(III)-organic complexes (particularly chromium dyes), was developed based on a column solid phase extraction using Amberlite XAD-4 resin (XAD-4). Acid Yellow 99 (AY99), a chromium monoazo dye, used as a model organic compound, could be quantitatively recovered at pH 5 with low recoveries of Cr(III) and Cr(VI) (below 5%). After Cr(VI) being converted to Cr(III)-diphenylcarbazone (Cr-DPC) by 1, 5-diphenylcarbazide, Cr(VI) was quantitatively recovered at pH 1 with the recovery of Cr(III) below 5%. The recoveries of AY99, Cr(III) and Cr(VI) by the newly developed method were 94.7±1.7, 103.0±2.5 and 96.7±3.6%, respectively. In addition, the recoveries of organics (i.e. proteins, amino acids, and organic acids) complexing with chromium ion were all below 5% at pH 1 and had little interference to the selective determination of Cr(VI) concentration. The adsorption capacity and detection limit of XAD-4 for Cr(VI) was 281.6±2.8 μg g^-1 and 1.37 μg L^-1, respectively.