Separation and Identification of SO₄^2-, S₂O₃^2-, S₃O₆^-2, and SO₆^-2 Anions by Means of Thin Layer Radiochromatography

Abstract

Thin layer radiochromatography is a useful means to investigate into intermediateoxyacid species of sulphur in low concentrations formed during aqueous reactions involving elemental sulphur and metal sulphides. In this study, 0.1-0.5 mol/dm3 standard solutions of commercial Na₂ SO₄ and Na₂ S₂O₃, synthesized Na₂ S₃O₆ and Na₂S₄O₆ were used to ensure identification of the anions. In an Ar glove box, 1-5×10^-3 cm³ of the solutions were dropped on a thin layer plate and dried. Development experiments were conducted in a glass cylinder in Ar at 22°C. It was found that a solvent containing ethanol, butanol, and water in the ratio 1: 1: 1 (vol.) and 0.5wt.-% KCH₃COO (pH 8.3), and the plate, TLC plastic sheets Cellulose No.5577 (Merk) gave best results for separating the thionate anions. Rf values obtained were 0.11, 0.20, 0.38, and 0.49 for SO₄^2-, S²O₃^2-, S₃O₆^2-, and S₄O₆^2-, respectively. From optical density measurements using films exposed to the developed plates, it was shown that the area of absorption peak (peak value x full width at half maximum) was proportional to the amount of S taken for all species. Two examples of the development were presentedbriefly. Sample solutions were taken from an ammoniacal copper solution where elimination of the copper was conducted by adding activated sulphur containing S. It was shown that S₃O₆^2- and S₄O₆^2- were formed during the reaction, whereas only S₂O₃^2- was found after completion of the elimination.