In many scientific fields, isotopic analysis can offer valuable information, e.g., for tracing the origin of minerals, agricultural products of plant or of animal origin or artifacts, for age determination, the elucidation of reaction mechanisms, and lately also for medical diagnosis. Up to date, isotope ratio measurements are performed on the entire elemental content of the sample. However, the analyte element is usually present under the form of different compounds, also called elemental species. Separating elemental species of interest from one another and from all other components of the sample that are not target analytes but may interfere with the measurements prior to isotope ratio measurements can provide species-specific isotopic information. This expanded information could be used for tracing the origin of environmental pollutants which are not the major species of the target element, or for the elucidation of speciation mechanisms.
Using multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS), the conventional analytical methods for isotope ratio measurements, the separation of different species has to be performed in tedious sample preparation procedures. A technically more elaborated approach was applied here: The hyphenation of MC-ICP-MS with an analytical separation technique. This way, the effort for sample preparation is minimized because the separation of elemental species is accomplished in the separation system (here: capillary electrophoresis), and the separated species are introduced directly (on-line) into the MC-ICP-MS.
With this hyphenated method, the isotopic composition of sulfur in sulfate originating from river water could be analyzed without sample preparation. The results were compared to data from conventional analysis of the same samples for validation. The precision of the results of the new method was promising regarding the differentiation of the river systems by the isotopic signature of river water sulfate. In a further experiment, it could be shown that also two elemental species in one sample could be analyzed with reasonable precision, allowing the isotopic analysis of both, natural and anthropogenic compounds in one single measurement.
Apart from the environmental field, this method could also be applied in the life sciences, such as the species-specific isotopic analysis of biomolecules like (metallo-)proteins.
Method development for on-line species-specific sulfur isotopic analysis by means of capillary electrophoresis/multicollector ICP-mass spectrometry
Sebastian Faßbender, K. Rodiouchkina, F. Vanhaecke, Björn Meermann
published in Analytical and Bioanalytical Chemistry, Vol. 412, pages 5637 - 5646, 2020
BAM, division Inorganic Trace Analysis