Microdetermination of divalent sulphur in aliphatic compounds by visual titrimetry, potentiometry, and atomic absorption spectrometry

Abstract

Divalent sulphur in structurally different aliphatic compounds including thiols, sulphides, disulphides and thiocarbonyls is selectively determined by reaction with solid potassium hydroxide at 250–280° for 5–10 min, followed by addition of alkali plumbite whereby lead sulphide is stoichiometrically formed. The excess lead ions are measured by: (a) atomic absorption spectrometry at 217 nm; or (b) potentiometric titration with EDTA at pH 4.6 using the lead ion selective electrode; or (c) visual titration with EDTA using urotropine buffer and Xylenol Orange indicator. An average recovery of 99%, and a mean standard deviation of 0.9% are obtainable with samples down to 2 mg. Divalent sulphur in many aromatic compounds, and tetra- and hexa-valent sulphur in both aliphatic and aromatic compounds do not interfere.