DETERMINATION OF SULFUR IN MILLIGRAM STEEL SAMPLES BY CATHODIC STRIPPING VOLTAMMETRY

Sulfur at the mug g-1 level in 1-mg steel samples is determined by cathodic stripping voltammetry (CSV) with a silver disk electrode, after conversion of the sulfur into hydrogen sulfide followed by its absorption in a 0.2 M sodium hydroxide solution. Microscale operations with microliter volumes of solutions are used throughout the entire procedure, except for CSV. Simple apparatus have been devised for a safe treatment with perchloric acid and for the evolution of hydrogen sulfide by reducing with a mixture of hydroiodic and phosphinic acids. The proposed method can be applied to the determination of 60 to 200 mug g-1 of sulfur in steels with an RSD of ca. 5% (n=3 to 10). The time required for a determination is less than 2.5 h.