Study of cross-linked poly(methacrylic acid) and polyvinylimidazole as selective adsorbents for on-line preconcentration and redox speciation of chromium with flame atomic absorption spectrometry determination

A redox speciation and preconcentration study of Cr(III) and Cr(VI) using a flow injection system with dual mini-columns prepared from cross-linked polymers-poly(methacrylic acid) and polyvinylimidazole was developed. Characterization of organic polymers was performed by using FTIR, SEM, TG, C:H:N and BET measurements. The equilibrium data obtained from Cr(III) adsorption on poly(methacrylic acid) and Cr(VI) on polyvinylimidazole were fitted very well to the dual site Langmuir-Freundlich model, suggesting the presence homogeneous and heterogeneous binding site and providing maximum adsorption capacities of 1.42 and 3.24 mg g− 1, respectively. The adsorption kinetics data were described by the pseudo-second-order model for both polymers, thus corroborating to isotherm data. The on-line preconcentration/speciation system was operated by loading 18.0 mL of a solution containing Cr(III) and Cr(VI) at pH 4.0 through the dual mini-columns at a flow rate of 3.0 mL min− 1, where Cr(III) was selectively retained on poly(methacrylic acid), while Cr(VI) was retained on polyvinylimidazole. The limits of detection were found to be 0.84 and 1.58 μg L− 1 for Cr(III) and Cr(VI), respectively. The preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were found to be 47.3/8.6, 0.38/2.1 mL and 7.88/1.43 min− 1 for Cr(III) and Cr(VI), respectively. The developed method was successfully applied to the speciation of chromium in different kinds of water samples. Satisfactory recovery values ranging from 89.9 to 108.3% were obtained.