Development of in-house reference materials for determination of inorganic polysulfides in water

In-house reference materials (IHRMs) for determination of inorganic polysulfides in water have been developed. The determination is based on the polysulfides’ derivatization with a methylation agent followed by GC/MS or HPLC analysis of the difunctionalized polysulfides. Therefore, the IHRMs are synthesized in the form of dimethylated polysulfides containing from four to eight atoms of sulfur. The composition of the compounds is confirmed by NMR and by the dependence of the HPLC retention time of the dimethyl polysulfides on the number of sulfur atoms in the molecule. Stability of the IHRMs is studied by HPLC with UV detection at 230 nm. Carbon tetrachloride solutions of the dimethyl polysulfides are stable at −20°C for 2 weeks, while their solutions in a mixture of acetonitrile and formic acid, 1:1, are stable even at +5°C for 3 weeks. The total sulfur content is controlled by the IHRMs’ oxidation with perchloric acid in high-pressure vessels (bombes) followed by determination of the formed sulfate using ICP-AES. Certified values of the dimethyl polysulfide concentrations are in the range of 416–3,327 ppm.