MC-MICAP-MS

Many metals and metalloids are abundant across natural systems and plays critical roles in many geological, chemical, and biological processes; producing significant isotope fractionation. Over the last decades, the high-precision analysis of radiogenic and stable isotopic ratios of various metal(loid)s has evolved as a powerful research tool with applications in diverse fields, such as geosciences, environmental sciences, (bio-)archaeological sciences, nuclear and forensic sciences, ecological and food sciences, life and biomedical sciences. 

The variations in radiogenic and stable metal(loid) isotopic compositions are significant and measurable among natural samples when using appropriate methods and suitable calibration strategies. Multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) is an established technique for high-precision isotopic analysis of various metal(loid)s, however, argon-related spectral interferences generated by the argon plasma limit analytical performance, especially for elements like calcium, iron, and selenium.

Instrumental strategies to cope with the argon-related spectral interferences include either high mass resolution to resolve the interferences or instruments that are equipped with a collision/reaction cell to enable chemical resolution of the interferences. These approaches can lead to reduced sensitivity, altered isotope fractionation behaviour, and instabilities associated with matrix effects.

An alternative strategy for eliminating argon-based interferences is to use a different plasma ion source that sustains a plasma with gases other than argon. Of particular interest is the microwave inductively coupled atmospheric-pressure plasma (MICAP) ion source, designed and marketed by Radom Instruments LLC, because it sustains a nitrogen plasma. Recently, Anika Retzmann (postdoc, 2023-2027) pioneered the integration of the MICAP ion source with high-precision multi-collector mass spectrometry for stable metal(loid) isotope analysis. We characterize the new MC-MICAP-MS instrument for its isotope performance for radiogenic strontium and stable calcium, iron, and selenium isotopes, with more to come. Furthermore, Gabby Gelinas (PhD, 2025-2029) is investigating the instrumental isotopic fractionation behavior of the new MC-MICAP-MS instrument using zinc isotopes as a model system.

MC-MICAP-MS represents a new approach in multi-collector mass spectrometry, enabling reliable and precise metal(loid) isotope ratio measurements without the limitations imposed by argon-based interferences. Given its broad range of potential applications, significant further work will be required to fully explore the capabilities of this new technology for the isotope research community.

This project is realized by funding from a NSERC-Discovery Grant, a Robson DNA Science Centre Postdoctoral Fellowship, an Eyes High Doctoral Recruitment Scholarship, and an Izaak Watson Killam Scholarship.