Fig. 6. Model applied to Cd and Zn competition data; Cd and Zn were present in solution. The background electrolyte was 0.1 M NaNO₃. Data are presented as the natural log of the ratio of bound to free metal ions ([M]_bound/[M]_free), modeled vs. measured. The bound species considered in Model A included: monodentate Cd–carboxyl complex (CdC), bidentate Cd–carboxyl complex (CdCC), bidentate Cd–(carboxyl + phenolic hydroxyl) complex (CdC), monodentate Zn–carboxyl complex (ZnC), bidentate Zn–carboxyl complex (ZnCC), and bidentate Zn–(carboxyl + phenolic hydroxyl) complex (ZnC). The values of constants and parameters used in Model A were: for Cd, –log intrinsic stability constant for metal complexationto a monodentate carboxyl binding site (pß_int^M,C)=0.290, –log intrinsic stability constant for metal complexation to a monodentate phenolic hydroxyl binding site (pß_int^M,)=4.76, proportion of carboxyl groups capable of forming bidentate chelates (P_CC) = 0.051, proportion of monodentate binding carboxyl groups capable of forming bidentate chelates to a phenolic hydroxyl group (P_C) = 0.951, and proportionality factor F_W = 0.169; for Zn,pß_int^M,C=0.968, pß_int^M,=4.52, P_CC = 0.171, P_C = 0.883, and F_W = 0.259.