Coupling of Capillary Electrophoresis with multicollector ICP-MS for species-specific isotope analysis of sulfur


D. Tukhmetova, S. Faßbender, B. Meermann

Federal Institute for Materials Research and Testing (BAM), Division 1.1 – Inorganic Trace Analysis, Unter den Eichen 87, 12205 Berlin

Sulfur is present in all proteins, in peptides and several other important biomolecules. Species-specific isotopic analysis of sulfur could offer detailed understanding of (bio)chemical and physiological processes. Therefore, efficient separation techniques coupled with reliable detection is required to measure slight variations in isotope ratio values in complex biological samples. As a proof of concept, capillary electrophoresis was coupled on-line with multicollector ICP-MS (CE/MC-ICP-MS) to separate naturally present sulphate from river water. Stable interfacing between CE and ICP was developed to provide reliable measurement. Open-source R programming language was used to perform automatic evaluation of transient signals in terms of isotope ratios to choose most suitable one among four known approaches. The on-line method was compared with traditional off-line method of separating analyte from matrix with ion exchange chromatography followed by MC-ICP-MS. Repeatability of the sulfate-δ34S value obtained with the on-line method was only two times higher than the off-line one, 0.57‰ (2SD) and (0.30‰, n = 68), respectively. Furthermore, the method is extended for the application for complex biological samples. This study includes initial results of analysis of animal blood serum to determine sulfur isotope ratio variations in Albumin fraction. The CE parameters of blood serum separation were modified to be compatible with MC-ICP-MS. Mass bias caused by instrumental mass discrimination is corrected externally by sample-standard bracketing procedure using matrix-match standard. The method presented in this study contributes to better understanding of the link between isotope ratio (delta) values and certain diseases in animal as well as in human body and might be a powerful diagnostic tool in the future.