The first work package aimed at exploring and optimizing the performances of the Proteus CRC-MC-ICP-MS prototype (developed by Thermo Fisher Scientific) for the analysis of K stable isotope ratios (41K/39K) and at establishing a protocol for the accurate and precise measurement of K stable isotope ratios. To this end, we explored the performances of the Proteus prototype in terms of precision and accuracy by developing an analytical strategy exploring the use of two different reaction gases. We compared its behaviour with measurements carried out using previously published data acquired with traditional MC-ICP-MS instruments and first generation of CRC- MC-ICP-MS instruments. This work led to the conclusion that the analytical methods developed for K isotopes on the Proteus are of high quality and competitive when compared to other more traditional technologies. This work also led to the constitution of a dataset of K isotope compositions of a series of 9 geological reference materials that will be made available to the community in a methodological publication.
The second work package aimed at developing a sample preparation procedure allowing precise and accurate analysis of K isotopes from a wide range of biological samples and reference materials while being versatile enough for geological materials processing as well. To this end, we adapted the K purification procedures for a wide range of biological samples. This chemical procedure was tested and met all quality criteria required for stable isotope analyses in a wide array of natural materials. We then calibrated the isotope compositions of a set of biological reference materials to provide the community with the basis for cross-laboratory benchmarking. This work notably led to the characterization of the K stable isotope compositions of a set of 7 biological reference materials with further successful quality controls.
The third work package aimed assessing the main mechanisms of K stable isotope cycling in vertebrate organisms. To this end, we measured the K isotope ratios of samples from biological materials and tissues (diet, blood plasma, red blood cells and whole blood, skeletal muscle and heart tissue, liver, bone, kidney, milk, fecal and urinary losses) of adult vertebrates reared in controlled feeding experiments for several animal model species. We built an unprecedented dataset of about 165 isotope compositions of these animal tissues. These results enabled us to assess the main mechanisms that drive K isotope fractionation at the organism level by first establishing the relationships between isotope compositions of the main K fluxes and reservoirs within vertebrate organisms. The dataset supports the predominant role of the transmembrane active transport of K as a key mechanism, with remarkably 41K enriched intracellular milieu in contrast with extracellular reservoirs (e.g. blood plasma). The study of the distributions of K isotopes in vertebrates also suggests that the homeostatic (K cycle regulation) response of the organism to varying dietary K availability plays an important role in the variability observed.
Throughout the BioIsoK project, the results of this research were presented in two main international conferences and an international workshop (Goldschmidt Conference and “Reaction Gases” workshop, 2020 Barcelona; 2020 Hawaii Goldschmidt conference). The dissemination of the results in scientific publications is due in the upcoming months in peer-review journals.
