Stability constants of Zn(II), Pb(II), Cd(II) and Cu(II) complexes with hematoxylin

The composition and stability constants of the complexes of Zn(II), Pb(II), Cd(II) and Cu(II) with hematoxylin have been studied using direct current polarography and differential pulse polarography. The results showed the formation of 1:2 (M:L) complexes for Zn(II) and Pb(II), and a 1:6 (M:L) complex for Cd(II). However, the formation of copper-hematoxylin complex is irreversible. The values of the formation constants for the above complexes at 298, 308 and 318K were calculated as well as the relevant thermodynamic parameters.