Determination of Stability Constants of Copper(II)-Glycine Complex in Mixed Solvents by Copper(II)-Selective Electrode

The first stability constants (in logβ1 form) of the Cu(II)-glycine complex have been determined at 25 °C and ionic strength of 0.10 mol/L in water and in mixed aqueous solutions of methanol (MeOH), ethanol (EtOH), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF) and 1,4-dioxane (DOX) from pH and pCu measurements of cells containing a copper(II) ion-selective electrode. In general, the stability constants of the complex increase with increasing composition of the co-solvents in the order: DOX>DMF>DMSO>EtOH>MeOH>H2O. An approximate linear relationship between logβ1 and the mole fraction of the co-solvent was observed for the complex in all the mixed solvents except in DMF+H2O mixtures. The response of the ion selective electrode to copper(II) ion in the mixed solvents was also investigated. The effects of solvent on the complex stability are discussed in terms of the polarity of the solvents.