Voltammetric determination of tin(II), tin(IV) and hydrolyzed tin in iron-zinc alloy plating solutions

Abstract

A method for determining Sn(II), Sn(IV) and hydrolyzed Sn has been developed in order to clarify the behavior of Sn in iron-zinc alloy plating solutions. Sn(II) was determined by differential-pulse anodic stripping voltammetry after reducing Fe(III) with ascorbic acid and masking Sn(IV) with H₃PO₄. Sn(IV) was determined by differentialpulse voltammetry in a Pyrogallol-HClO₄ solution with correction for the overlapping peak of Sn(II). The total Sn was determined by differential-pulse anodic stripping voltammetry after dissolving hydrolyzed Sn with HCl and oxidizing Sn(II) with H₂O₂. Hydrolyzed Sn was calculated as the difference between the total Sn and Sn-ions {Sn(II)+Sn(IV)}. Sn (II), Sn (IV) and the total Sn in an iron-zinc alloy plating solution containing 10 mg dm^-3 of Sn(II) and 10 mg dm^-3 of Sn(IV) were determined with a relative standard deviation of about 5%. The present method revealed that Sn(II) was appreciably stable in plating solutions. In addition, it was found that the presence of Fe (III) in the plating solutions accelerated the oxidation of Sn(II) to Sn(IV), which was finally hydrolyzed.