Spectrophotometric Determination of Micro-amounts of Sulfide on the Surface of Tin-plated Articles by the Methylene-blue Method

Abstract

This paper describes about an analytical method for evaluating the degree of sulfide stain on the surface of tin-plated articles treated with sulfur-containing solutions. The method is based on the difference in the solubilities of the sulfide and the iron matrix in a dilute hydrochloric acid.
The outline of procedure is as follows:
To disslove all the sulfide on the surface, the sample is treated with 20ml of 2N hyrdochloric acid at room temperature for 20 minutes under passing nitrogen gas. The evolved hydrogen sulfide is absorbed in a zinc acetate solution and caught as zinc sulfide. Then methylene blue is formed by the reaction of the sulfide ion with P-aminodimethylaniline in the presence of ferric chloride. The microamounts of sulfide on the surface of the sample is determined by measuring the absorbance of the methylene-blue at 660mμ.
By this method, several samples (sulfide-treated tin-platings) were analysed and the satisfactory results were obtained.