Amberlite XAD-2 functionalized with chromotropic acid: synthesis of a new polymer matrix and its applications in metal ion enrichment for their determination by flame atomic absorption spectrometry

Abstract

Chromotropic acid has been covalently linked with the benzene ring of Amberlite XAD-2, through an –NN– group, to design a new polymer matrix. Elemental analyses, thermogravimetric analyses and infrared spectra were used to characterize the resulting functionalized Amberlite XAD-2. It was used for the separation and preconcentration of Cd^II, Co^II, Cu^II, Ni^II, Fe^III and Zn^II prior to their determination by flame atomic absorption spectrometry. The optimum pH values for quantitative sorption are 5.0–6.0, 4.0–4.5, 4.5–5.5, 4.0–5.0, 5.0–6.5 and 5.5–7.0 for Cd^II, Co^II, Cu^II, Fe^IlI, Ni^II and Zn^II, respectively. All these metal ions can be desorbed with 2 mol l^–1 HCl or HNO₃ (recovery, 96–100%). The sorption capacity of the resin is 9.35, 3.84, 8.50, 3.24, 6.07 and 9.65 mg g^–1 of resin for Cd, Co, Cu, Ni, Fe and Zn, respectively. Tolerance limits for electrolytes NaCl, NaBr, NaNO₃, Na₂SO₄ and Na₃PO₄ on the sorption of these metal ions are reported. NaNO₃, Na₂SO₄ and Na₃PO₄ are tolerable up to a concentration level of a few millimoles in the sorption of 0.1 mg l^–1 Cd. Similarly, NaNO₃ with Cu (0.1 mg l^–1) and Na₃PO₄ with Fe (0.1 mg l^–1) interfere when their concentration exceeds a few millimoles. The enrichment of all of these metal ions is quantitative in the presence of 0.1 mol l^–1 of Mg^II and Ca^II. The preconcentration factors are found to be 100, 150, 100, 120, 200 and 200 for Cd, Co, Cu, Fe, Ni and Zn (concentration level, 5–10 µg l^–1), respectively, and their respective t_1/2 values are 2.6, 4.3, 2.9, 5.8, 3.4 and 2.4 min. The simultaneous determination of Cd, Co, Cu, Fe, Ni and Zn is possible. The method was applied to the determination of these six metal ions in river water samples (RSD < 7.8%). Cobalt contents of pharmaceutical samples (vitamin tablets) were preconcentrated by the present chelating resin and estimated by flame atomic absorption spectrometry, with RSD < 1.1%.