A new method for transforming trace amounts of elemental sulfur dissolved in hydrocarbons quantltatively to thiosulfate is developed. The sensltlvlty and accuracy of the method were checked by titratlng 1 m L samples of sodlum thlosulfate containlng sulfur in the range of 3.22 X to 6.85 X lo-'

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A potentiometric method is described for the determination of elemental sulphur in petroleum and petroleum fractions over all concentration ranges. The method involves the conversion of elemental sulphur into a homogeneous thiosulphate solution, followed by potentiometric titration using mercury(l1) chloride as titrant with a sulphide-selective indicator electrode.The accuracy and reproducibility of the method were established by titrating several synthetic standards dissolved in heptane in which the free sulphur, at levels ranging between 1.0 x 10-3 and 1.0 x 10-1 g, was converted quantitatively into homogeneous thiosulphate solutions containing from 4.0 x 10-6 to 4.0 x 10-4 g ml-l of elemental sulphur. The results obtained, expressed in the form of a Gran plot, showed an error ranging from 0.88 to 2.33% by mass. The range of concentrations of elemental sulphur in crude oil and eleven petroleum fractions ranged from 1.83 x lO-3% by mass in heavy naphtha to 4.62 x lO-5% by mass in hydrotreater kerosene, with a relative standard deviation ranging from 1.20 to 5.61%.