ISO International Standard

Relates to products boiling below 200 °C. Directly applicable to contents of 0.1 mg/kg to 30 mg/kg. Higher contents may be determined by a suitable dilution of the sample. Alkylsulphones, arylsulphonic acids and arylsulphonates give incomplete recovery of sulphur. Reduction of the sulphur compounds to nickel sulphide with Raney nickel. Stripping of the hydrogen sulphide in hydrochloric acid medium and absorption in an alkaline zinc acetate solution. Formation of methylene blue with N,N-dimethyl-p-phenylenediamine sulphate and iron(III) ammonium sulphate. Determination of the absorbance of the blue coloured solution at a wavelength of 667 nm.