S. Dalby, S. Milano, G. Craig, M. Pfeifer, C. Bouman and N. S. Lloyd
Thermo Fisher Scientific, Hanna-Kunath Str. 11, 28199 Bremen, Germany

Accurately constraining lowest abundance Th and U isotopes has become an important tool in geochronology and for nuclear forensics, e.g., in dating geologically young samples or controlling nuclear proliferation. Multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been used to accurately and precisely measure the isotopic composition of uranium for over two decades1-3. Due to uranium enrichment, samples often have a wide range of potential isotopic ratios, which is a challenge for analysis. In addition, the large abundance of the main isotopes 235U and 238U hamper measurements of smallest 234U and 236U intensities due to tailing effects superimposing on the lower signals.
The Thermo Scientific™ Neoma™ MC-ICP-MS offer several advantages to tackle these challenges. The 1013Ω amplifier technology extends the dynamic range of the Faraday Cup detectors, giving superior precision compared to 1011Ω amplifiers at signal intensities between several 10kcps to 10s of Mcps, related to their better signal-to-noise ratio3.
The combination of the game-changing novel pre-cell mass filter and hexapole collision/reaction in a Neoma MS/MS MC-ICP-MS4 with the RPQ allows an abundance sensitivity of better than 50 ppb at 1 amu for 238U. This is an order of magnitude improvement when compared to a conventional Neoma MC-ICP-MS with an RPQ.
We present Uranium isotope ratio measurements for the IRMM-183 to IRMM-187 series standard reference materials performed with improved abundance sensitivity on the Neoma MS/MS MC-ICP-MS. An amplifier with 1013Ω resistor was applied for the 234U/238U ratio determination and the 236U/238U measurements were recorded with a secondary electron multiplier (SEM) applying optimized RPQ settings to reduce the peak tail from 238U to single cps.
1.    K. Yamamoto, O. Takeshi, G. Kitamura, H. Takahashi, and T. Hirata, Environmental Technology & Innovation., 2024, 36, 103761–103769.
2.    S. F. Boulyga, A. Koepf, S. Konegger-Kappel, Z. Macsik and G. Stadelmann, J. Anal. At. Spectrom., 2016,31, 2272-2284.
3.    N. A. Zirakparvar, B. Manard, C. Hexel, D. Dunlap, S. Metzger, D. Bostick, V. Bradley, B. Ticknor, International Journal of Mass Spectrometry, 2023, 492, 117114-117123.
4.    G. Craig, H. Wehrs, D. G. Bevan, M. Pfeifer, J. Lewis, C. D. Coath, T. Elliott., C. Huang, N. S. Lloyd and J. B. Schwieters, Anal. Chem., 2021, 93, 10519-10527.