Characterization of immobilized poly(L-cysteine) for cadmium chelation and preconcentration

Poly(L-cysteine) (PLC) was successfully immobilized on controlled-pore glass (CPG) and used in a now injection system incorporating a microcolumn for separation of Cd from synthetic solutions, On-line breakthrough curves were used to study the effect of pH, concentration, and influent flow rate on Cd adsorption, The Cd breakthrough experiments revealed a significant strong-site capacity as well as weaker binding sites that showed a dependence on influent concentration, In addition, increased capacity was observed at more alkaline pH values, The now rate studies showed nonequilibrium conditions existed for Cd binding at flow rates of 0.55-3.75 mL/min, with decreased capacity for faster flow rates, Elemental analysis of immobilized PLC for sulfur estimated 6.8 x 10(-6) mol of PLC/g of CPG and the calculated mole ratio of Cd to PLC was 6.2:1 at pH 9. Stability constants governing the Cd adsorption by PLC were obtained by a nonlinear least-squares analysis of the Cd binding data and revealed at least four classes of binding sites were present and that the stable Cd complexation observed for the free molecule was retained by immobilized PLC. Stability constants for the most stable sites were estimated using EMTA and en as competing ligands and resulted in two sites: K-1 = 1 x 10(13) and K-2 = 10(9) - 10(11) with capacities of nl = 1 mu mol/g and and n(2) = 6 mu mol/g, respectively. Two weaker binding sites were also identified and represented by stability constants of K-3 = 1 x 10(6) and K-5 = 2 x 10(4) with Site capacities of n(4) = 20 mu mol/g and ns = 10 mu mol/g, respectively.