Determination of manganese(II) in cyanide medium by volumetric and coulometric titration with hexacyanoferrate(III)

Abstract

A volumetric titration of manganese(II) may be carried out with hexacyanoferrate(III) in cyanide medium under an inert atmosphere with a potentiometric, amperometric or biamperometric end-point. In very strong NaCN solution or at high temperature, positive errors are produced by the Fe(CN)₆^3–-CN^– reaction. At lower cyanide concentrations errors become negative owing to manganese(II) oxidation with dissolved oxygen. In 2.0 M NaCN solution, 1–5 mmol of manganese(II) may be titrated with a 0.2–0.3% relative error. A relative standard deviation for a 2.5-mmol determination is 0.14%. Foreign ion effects were studied and methods for avoiding interferences from Fe(II), Fe(III) and V(IV) are described. The proposed procedure was applied to slag analysis.

Coulometric titration of 2.5–100 µmol of manganese(II) with electrogenerated hexacyanoferrate(III) may be carried out in 1.0 M NaCN solution with relative errors lower than 0.4%. The relative standard deviation for the determination of about 120 µmol of manganese(II) is 0.01%.