Electroanalytical procedures:
Why is a high supporting electrolyte concentration used in most electroanalytical procedures
Answer:
According to Ilkovic equation, id is proportional to η1/2. η varies as the aqueous solution changed partly to non-aqueous medium using solvents such as methanol, dioxane etc. modification in the composition of the supporting electrolyte through adding complexing ligands to the electrolyte solution changes the size of the metal complex and therefore D of the ion. id therefore decreases with complexation and E1/2 shifts to more negative potentials.
It is essential to keep the concentration of every constituent of the supporting electrolyte constant within about + 10% to ensure the variation of id resulting from this effect (viscosity) will be negligibly small.