Anion exchangers functionalized by chelating reagents (AnChel) for preconcentration of trace elements: Capabilities and limitations

Summary

Conventional anion exchangers (e.g., Adsorbex SAX, Amberlite IRA 410, Dowex 1X8, Lewatit MP 5080, TEAE cellulose) functionalized by means of sulfonated metal reagents (e.g., Arsenazo III, Eriochrome Red B, 8-hydroxyquinoline-5-sulfonic acid, Tiron and others) were investigated as collectors (AnChel) for analytical preconcentration of trace elements. In particular, the stability of AnChel strongly depending on competing anions, on the anion exchanger and on the metal reagent chosen, was characterized. Accordingly, for appropriate combinations of AnChel (e.g., Dowex 1X8/Arsenazo III) reagent distribution coefficients K_d in the range 10⁴ to 10⁵ (ml/g) could be attained on polystyrene-based anion exchangers even in concentrated salt solutions (e.g., 4 mol/l NaCl), but not on hydrophilic exchangers (e.g., SAX, TEAE cellulose). In general, the stability of AnChel against competing anions followed the order Cl⁻>SO ²⁻₄ >NO ⁻₃ >ClO ⁻₄ . Reagent loadings of about 1 mmol/g (e.g., 8-hydroxyquinoline S) on the anion exchangers were obtainable. Trace metals precomplexed with the reagents cited could be separated (>90%) within 5 min and remobilized by acid (e.g. 2 mol/l HNO₃) within some 10 s (batch procedure). Using small columns filled with anion exchanger (e.g., 0.25 g Dowex 1X8) fast trace-matrix separations were carried out with 8-hydroxyquinoline S (Cu, Fe, In, Mn, Pb, Zn) in MgCl₂ solutions and with Arsenazo III (U, Th) in AlCl₃ solution, respectively. For subsequent trace determinations the flame-AAS (injection technique) was applied, except for Th and U [quantified by total reflection X-ray fluorescence (TXRF)].