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

Due to the wide range of natural abundances for its six naturally occurring nuclides and the high number of potential interferences, high precision measurement of the Ca isotope system has always been challenging. Most obviously for those wishing to use multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) to measure Ca is the isobaric overlap between 40Ar+, the single largest component of the ICP, and 40Ca+. MC-ICP-MS has for some time used to measure 42Ca – 48Ca1, but it is only in the last few years, with the re-introduction of collision/reaction cell technology to MC-ICP-MS, that it has been possible to report δ44/40Ca with MC-ICP-MS2,3, instead of a double spike TIMS method. The addition of H2 (alongside He) to the collision/reaction cell neutralizes the 40Ar+ ion to 40Ar0, allowing the 40Ca to be measured interference free.
However, there is another potential mechanism to measure 40Ca+ free from 40Ar+ with a MC-ICP-MS. Like its fellow alkaline earth element Sr4, Ca+ ions readily react with SF6 in a collision/reaction cell to form CaF+. This has the potential to eliminate not only the 40Ar+ interference on 40Ca+, but also the interference of 88Sr2+ on 44Ca+. This opens the possibility of measuring high precision Ca isotope ratios in-situ for solid samples via laser ablation. Here we report our investigations into using SF6 as a reaction gas to measure high-precision calcium ratios with a Thermo Scientific™ Neoma™ MS/MS MC-ICP-MS for both solution and solid samples.
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