All solutions were prepared by using doubly distilled water. The
stock solutions of Pb (II) and Cd (II), 1000 mg/L, were prepared by a
careful weighting of solid lead nitrate and cadmium nitrate
(Merck) and dissolving in distilled water in two 100 ml volumetric
flasks. A stock solution of 1.0 103 M 2-mercaptobenzothiazole
(Merck) was prepared by dissolving 0.01672 g of the compound
in 100.0 ml water. Borate buffer solutions (pH 6.0–10.0) were prepared
by mixing different amounts of boric acid, 0.1 M, and NaOH
(0.1 M) in a 100.0 ml volumetric flask.