The Finow Canal has now become a recreational and touristic area. The picture shows one of the twelve heritage-protected locks.
Source: BAM, division Inorganic Trace Analysis
The properties (e.g., toxicity, mobility) of elements depend on the species (here: oxidation state and bonding state) in which they are present. Therefore, it is important to study the distribution of elemental species, especially in environmental systems. However, the analysis of the speciation of an element is not a simple task, because it depends on the ambient conditions and can change especially during sample preparation for the analysis leading to wrong results. An elegant strategy to avoid this problem is the isotope dilution analysis (IDA). In IDA, a known amount of the elemental species with a defined – but different from the natural - isotopic distribution of the element is added to the sample before preparation. Since the natural isotopic distribution is also known, the original amount of the species in the sample can be calculated after measuring the isotope ratio of the mixed sample. This approach has the advantage that any changes in speciation during sample preparation can be accounted for and, in addition, the results are very accurate because isotope ratios can be measured very precisely using mass spectrometry (MS).
In this work, the suitability of ICP-ToF-MS (time-of-flight mass spectrometry with inductively coupled plasma) as a detector of a gas chromatographic separation to achieve higher accuracy in IDA was investigated. Since an ICP-ToF-MS can measure all isotopes simultaneously, there is at least a theoretical advantage for high-precision measurements of isotope ratios over classical ICP-MS technologies.
The analysis of the speciation of mercury in sediments from the Finow Canal was chosen as a case study. Mercury is a heavy metal that is highly toxic to living organisms, particularly in the form of methylmercury, and biomagnifies in the food chain. The Finow Canal is known to be a polluted water body, as a number of industrial companies settled on its banks in the 20th century and used it to dispose of wastewater. Mercury has earlier been detected in high concentrations in the sediment, but a speciation analysis has not yet been performed.
In this work, the (dry) sediment was found to be contaminated with methylmercury in the µg/kg range using the IDA procedure. Compared to the unpolluted part of the Finow Canal this is a strongly increased concentration.
Species-specific isotope dilution analysis of monomethylmercury in sediment using GC/ICP-ToF-MS and comparison with ICP-Q-MS and ICP-SF-MS
Sebastian Faßbender, Marcus von der Au, Maren Koenig, J. Pelzer, Christian Piechotta, Jochen Vogl, Björn Meermann
published in Analytical and Bioanalytical Chemistry, Vol. 413, issue 21, pages 5279 - 5289, 2021
BAM, division Inorganic Trace Analysis and division Environmental Analysis