Inorganic chemicals were supplied by Merck as analytical-grade reagents and deionized water was used.
The metal ions studied were Co(II), Cu(II), Zn(II), and Mn(II).
We prepared a synthetic stock solution of copper, manganese, and cobalt using their nitrate salts, Cu(NO3)2·3H2O,
Mn(NO3)2·4H2O, and Co(NO3)2·6H2O, respectively, in deionized water.
The stock solution of Zn(II) was prepared using ZnCl2 salts.