A new chelating resin containing azophenolcarboxylate functionality: synthesis, characterization and application to chromium speciation in wastewater

The synthesis of a new stable chelating resin from the polystyrene divinylbenzene copolymer is reported. The polystyrene is first functionalized with a phenolic group and then allowed to couple with diazotized anthranilic acid through the NN bond. The resulting polymer containing azophenolcarboxylate with an ONO chelating environment has been characterized by elemental analysis, hydrogen ion capacity, and water regain value. Its stability towards thermal and different chemical environments has been evaluated. The sorption capacity of the chelating resin for Cr(III) and Cr(VI) as a function of pH has been studied. The interesting point is that chromium(III) is selectively retained at ca. pH 5.0 and chromium(VI) at ca. pH 2.0. When packed in a column, the new material is able to separate Cr(III) from Cr(VI). Five replicate determinations of 10 μg Cr(III) and 10 μg Cr(VI) present in 100 mL solution gave recoveries of 96.9 ± 2.9% (for Cr(III)) and 96.2 ± 2.1% (for Cr(VI)) at the 95% confidence level. Calibration graph was linear over the concentration range of 0-250 μg L⁻¹ of chromium species with correlation coefficient (R) of 0.99994. The detection limits based on 3σ criterion were determined to be 0.6 μg L⁻¹ for Cr(III) and 0.9 μg L⁻¹ for Cr(VI). The developed method was successfully used for the speciation of chromium in wastewater.