Metal ion enrichment with Amberlite XAD-2 functionalized with Tiron: analytical applications

Abstract

Amberlite XAD-2 was functionalized with Tiron (disodium salt of 1,2-dihydroxybenzene-3,5-disulfonic acid) by coupling it through an –NN– spacer. The resulting chelating resin, characterized by elemental analyses, thermogravimetric analysis and infrared (IR) spectra, was used to preconcentrate Cu^II, Cd^II, Co^II, Ni^II, Pb^II, Zn^II, Mn^II, Fe^III and UO₂^II. They were determined by flame atomic absorption spectrometry, except for uranium, for which fluorimetry was used. The pH ranges for quantitative sorption were 4.0–6.0, 4.5–6.0, 5.0–7.0, 5.0–6.0, 4.0–5.5, 5.0–6.0, 6.5–7.5, 5.0–6.0 and 4.5–5.5, for Cu, Cd, Co, Ni, Pb, Zn, Mn, Fe and U, respectively. All these metal ions can be desorbed (recovery 91–99%) with 4 mol l⁻¹ HNO₃ or HCl, except for uranyl ion, for which only 4 mol l⁻¹ HNO₃ is suitable. The sorption capacity of the resin was 14.0, 9.5, 6.5, 12.6, 12.6, 11.1, 10.0, 5.6 and 7.7 mg of metal ion per gram of resin, respectively, for the nine metals. The loading half time (t_1/2) was less than 5 min for all the metal ions. The effects of NaF, NaCl, NaNO₃, Na₂SO₄, and Na₃PO₄ on the sorption of these metal ions (0.2 μg ml⁻¹) are reported. Ca^II and Mg^II are tolerated with each of them (0.2 μg ml⁻¹) up to a concentration level of 2–30 and 2–10 mmol l⁻¹, respectively. The enrichment factors for Cu^II, Cd^II, Co^II, Ni^II, Pb^II, Zn^II, Mn^II, Fe^III and UO₂^II were 200, 50, 55, 150, 25, 180, 65, 80 and 150 (concentration level 2–25 μg l⁻¹), respectively. The limits of detection for these metal ions are 2.0, 1.3, 5.0, 4.0, 24.0, 0.5, 2.5, 5.0 and 1.0 μg l⁻¹, respectively. Simultaneous enrichment and determination of all the metal ions is possible. The flame AAS method was applied to determine these metal ions (except uranyl ion) in river water samples (RSD ⩽8%) after their enrichment with the present matrix. Uranium in well water samples and cobalt contents of pharmaceutical vitamin tablets were also determined fluorimetrically (RSD <5%) and by flame AAS (RSD ≡3%), respectively, after enrichment on the present resin.