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The Determination of Total Sulphur in Geological Materials by Coulometric Titration

“The Determination of Total Sulphur in Geological Materials by Coulometric Titration” Chemical Geology 111 (1994): 131-134.

Brian P. Atkin and Chris Somerfield

Department of Mineral Resources Engineering, University of Nottingham NG7 2RD, UK.

Determination of these methods range from 50 ppm for XRF 2 ppm for ion chromatography.
One of the main problems relating to the analysis of sulphur in geological materials is the poor quality of the available geochemical reference standards required for the calibration and quality control of instrumental analysis. This is demonstrated by examining compilations of the values reported for Geochemical Reference Standards. It is clear by examining such compilations that the reported data for sulphur is highly variable and is therefore unreliable. The data quoted by Gladney and Roelandts (1990) for the Geochemical Exploration Samples GXR-1 to GXR-6 illustrates this point very well. Quoted data for GXR-1 range from 2300 to 4700 ppm, for GXR-2 from 275 to 2300 ppm, for GXR-3 from 1700 to 17000 ppm, for GXR-4 from 1.68 to 1.88 %, for GXR-5 from 200 to 2300 ppm and for GXR-6 from 100 to 25400 ppm. Even if obvious outliers are removed from the range the variability of the quoted data is still large and often unacceptable foe use as primary standards. Many of the techniques which require standardization have had to rely on synthetic or simple chemical standards which may not adequately match the matrix of geological samples.

We have tested a UIC Model 3200 Sulphur coulometer on samples ranging in sulphur content from a few parts per million to several per cent. The main advantage of this technique is that it does not require calibration against natural or synthetic standards and therefore the data should be independent of the problems associated with the low quality data available for geochemical reference standards. Most of the samples quoted in this paper are recognized geochemical reference standards and comparisons are given to the values quoted in Govindaraju (1989).