Calcium isotopic composition of widely available biological reference materials using collision cell (CC)-MC-ICP-MS

Background: The application of isotopes of metals in medical science (isotope metallomics) has shown significant growth in the last few years, specifically with respect to the study of metal cycles in the body and/or their use as diagnostic tools for diseases that affect metal homeostasis. Given the great potential for Ca stable isotopes to identify changes in Ca metabolism and bone metabolism, there have been major applications of Ca metallomics—and isotope metallomics. However, reliable and high precision Ca isotopic analysis is challenging considering the limited Ca amounts in some soft tissues compared to e.g., bones and the related interference effect during measurement. Furthermore, there is a lack of Ca isotopic data in widely available biological reference materials with various matrices. Method: The development of collision-cell multi-collection inductively-coupled-plasma mass-spectrometers (CC-MC-ICP-MS), such as the Nu Instrument Sapphire, has revolutionized Ca isotope analysis, improving the sensitivity by over a factor 10 compared to older generation instruments, and more readily overcoming isobaric interferences. In this study, we report the first set of high precision Ca isotopic data for several widely available biological reference materials, spanning both land and sea animals, as well as various bodily organs (muscle, kidney, liver). Result: Results indicate that animals are globally enriched in the lighter isotopes compared to their living environment, and that Ca isotopes are fractionated by more than 1.5 ‰ between organs (e.g., in bovine), further highlighting that Ca isotopes could be used to study Ca cycles within the body. Conclusion: These new data—and reference materials—could be used for future interlaboratory comparisons.