Equilibria of the Simultaneously Existing Multiple Species in the Copper(II)–L-Histidine System

Abstract

The complete species distribution and the stability constants of the complex species in the Cu(II)–L-histidine system have been worked out for the pH range 2–11. The method of "analytical potentiometry" has been applied successfully to this system having excess ligand with respect to Cu(II) ion. The equilibria of three systems of Cu(II) (M) and L-histidine (H₃A) in molar ratios of 1:2, 1:4, and 1:8 were investigated by this technique in 0.15 M NaCl at 25°. The following species were detected in this system: MHA, MA, MH₂A₂, MHA₂, MA₂, MH₋₁A₂, MH₋₁A, and M₂H₋₂A₂. Statistical analysis on the numerical results has been performed and is given as standard deviation together with the individual values for the stability constants.