Chapter 27 - Direct Measurement of the Content and Isotopic Composition of Sulfur in Black Shales by Means of Combustion-Isotope-Ratio-Monitoring Mass Spectrometry (C-irmMS)

Abstract

The content and sulfur isotopic composition of black shales are directly measured by means of combustion-isotope-ratio-monitoring mass spectrometry (C-irmMS). The results are compared to the Kiba reagent method for sulfur isotope preparation and the coulometric method for determination of the concentration. This chapter discusses the determination of the contents and concentrations and sulfur isotopic composition of sulfur species in modern and ancient sediments is of fundamental interest for the evaluation of biogeochemical reactions in the coupled sedimentary element cycles. The C-irmMS measurements are not disturbed by the common combustion of sulfur- and carbon-bearing compounds up to 13 wt.% C. The C irmMS method is successfully applied to a set of different pure synthetic and natural sulfur- bearing compounds and natural shale geostandards. The results shows a good agreement, indicating that C-irmMS is a powerful analytical tool both precise and fast in sample preparation, which needs only small amounts of sample material. Therefore, for a detailed analysis of microbial reactions leading to an isotope fractionation among different sulfur bearing-species especially in recent marine sediments or bacterial cultures, the chemical separation of the different sulfur phases may be necessary.