Potentiometric determination of sulphur in solid samples with a sulphide selective electrode

Up to date the potentiometric analysis of low sulphur amounts present in solid samples has been made by reducing the solid sample and absorbing the formed H2S(g) in an appropriate solution (basic and resistant to sulphur oxidation). The total sulphur content of the solution is then analysed either by direct measurement or by potentiometric titration via a sulphide selective electrode. However, all the reported techniques make use of a previous standardisation with solid samples of known sulphur content, in order to avoid the error produced by the losses of sulphur in solution during the long titration times. These losses are especially significant for sulphur concentrations below 10(-3) M. Standardisation is a time-consuming process, which introduces an additional error by assuming a linear dependence of the sulphur losses on the sulphur concentration of the solution. In this work, standardisation is proven to be unnecessary if the potentiometric titration of the solution is substituted by the direct measurement of its sulphur content via the sulphur selective electrode. In this way the analysis times are drastically reduced, and therefore, the sulphur losses are minimised. Standardisation is thus replaced by a less time-consuming calibration of the electrode with few solutions of known sulphur concentration. This method is recommended especially for solutions with sulphur concentrations below 10(-3) M. (C) 1999 Elsevier Science B.V. All rights reserved.