Evaluation of copper speciation in the extract of Eichhornia crassipes using reverse and forward/CLE voltammetric titrations

Abstract

Reverse and forward titrations coupled with the competitive ligand equilibration (CLE) technique were, for the first time, used to investigate the chemical organic speciation of copper ions in an aqueous extract of Eichhornia crassipes (E.C) plant growing in Egypt. Salicylaldoxime (SA) was used as the competitive ligand. Two samples were collected from huge submerged masses in the Nile water at Sohag and Mansura cities. In this study the concentration of the natural complexing ligands (CLn) and their conditional stability constants with copper (KCuLn′) in the aqueous extract were determined by linear and nonlinear modeling. Reverse titration resulted in two classes of copper complexation (CuL1 and CuL2) in both samples. The strongest class, CuL1, is predominant in Sohag-sample with average logKCuL1′ and CL1 of 15.66 and 435.5nM, respectively, and also dominated in the Mansura-sample with average 16.77 and 162nM, respectively. The second class (CuL2) is minor in both samples. For comparison, forward titration was performed for the Sohag-sample. The results indicated that reverse titration showed a breakthrough ability to detect, for the first time, different types of metal complexation present in equilibrium in the aqueous extracts of biological samples. Moreover, the presence of E.C in Nile water is so useful in transforming free Cu ions to less toxic forms by organic complexation.