Iodimetric titration of metallic zinc powder for paints

Abstract

The determination of the active metallic component in zinc dust for paints was conveniently determined by an iodimetric procedure in the presence of EDTA (H₂Y^2–, pH 5.3) to attack the ZnO protecting film. A precision of ±0.25%(95% confidence level) was attained for 0.13–0.15 g of zinc plus 25 ml of 0.1 mol l^–1 I_2–I^– solution with back-titration with 0.1 mol l^–1 S₂O₃^2–. The procedure was also applied to dry powdered paints in the presence of 5 ml of chloroform to attack the organic layer. Comparison with a modified permanganometric ASTM procedure for zinc dust, using an Fe^III–acetate reagent, showed a higher precision for the iodimetric method.