Abstract This study presents a new technique for high precision measurement of iron isotope ratios using high mass resolution MC-ICPMS on the ThermoFinnigan Neptune. A mass resolving power of about 8000–9000 was used to resolve the mass interferences of isobaric polyatomic ions (e.g., 40 Ar 16 O + on 56 Fe + , 40 Ar 16 OH + on 57 Fe + and 40 Ar 14 N + on 54 Fe + ) from the Fe isotopes and to produce “flat top” peak shapes with a plateau width of about 100 ppm in mass (Δm/m). The abundance sensitivity was determined to 50 ppm contribution of the 40 Ar 16 O + peak tail on the 56 Fe + peak. This enables Fe isotope measurements with a Fe-isotope/interference ratio of up to 1, without significant contribution from the tail of the interference peak. The performance of the technique was tested by determining the reproducibility and accuracy of synthetic Fe samples and spiked standards against the IRMM014 standard. Various interface setups, including wet and dry plasma techniques, and a wide range of concentrations (from 50 ppb to 10 ppm) have been used to demonstrate the flexibility, robustness and sensitivity of the technique. An external precision of ca. 0.10‰ for δ 56 Fe and ca. 0.15‰ for δ 57 Fe (2 S.D.) was routinely achieved. Measured and calculated delta values between spiked standards and the IRMM014 standard agree within uncertainties. In the investigated concentration range, precision and accuracy are independent of both the sample introduction system and the sample concentration. The new technique presented in this study is a robust and simple method to perform high precision Fe isotope measurements, and it allows to measure much lower sample concentrations compared to previous techniques.

High Precision Iron Isotope Measurements With High Mass Resolution MC-ICPMS

Molybdenum in natural waters: A review of occurrence, distributions and controls

https://originslab.uchicago.edu/sites/default/files/articles/87_Tissot_Dauphas_GCA_2015.pdf

Uranium isotopic compositions of the crust and ocean: Age corrections, U budget and global extent of modern anoxia

> “The Answer to the Great Question... Of Life, the Universe and Everything... 
> 
> Is... Forty-two,” said Deep Thought, with infinite majesty and calm… 
> 
> “I checked it very thoroughly,” said the computer, “and that quite definitely is the answer.” 
> 
> — Douglas Adams, The Hitchhiker’s Guide to the Galaxy 
Molybdenum (Mo)—the element with atomic number 42—possesses unique properties that make it the answer to many questions in the geosciences, life sciences, and industry.

In the geosciences, the redox sensitivity of Mo makes it particularly useful for answering questions about environmental redox conditions. In particular, it was first suggested as an ocean paleoredox proxy over 30 years ago (Holland 1984; Emerson and Huested 1991)—an application that finally came to fruition in the late 1990s and 2000s when understanding of Mo geochemical behavior in modern environments improved significantly (e.g., Crusius et al. 1996; Helz et al. 1996, 2011; Morford and Emerson 1999; Erickson and Helz 2000; Barling et al. 2001; Siebert et al. 2003, 2005; Arnold et al. 2004; Vorlicek et al. 2004; Morford et al. 2005; Nagler et al. 2005; Algeo and Lyons 2006; McManus et al. 2006; Poulson et al. 2006; Anbar et al. 2007; Wille et al. 2007; Pearce et al. 2008; Archer and Vance 2008; Neubert et al. 2008; Scott et al. 2008; Gordon et al. 2009; Poulson Brucker et al. 2009).

In the life sciences, nature settled on Mo as the answer to the challenge of biological-N2 fixation at least ~ 2 billion years ago (Boyd et al. 2011), with the evolution of the Mo-dependent nitrogenase enzyme. Molybdenum is also at the heart of nitrate reductase enzymes, which are essential for assimilatory and dissimilatory nitrate reduction (Glass et al. 2009). Therefore, Mo is central …

/pdf/the-stable-isotope-geochemistry-of-molybdenum-5eblplscoa.pdf

The Stable Isotope Geochemistry of Molybdenum

This review focuses on the rapidly growing field of natural 238U/235U variability, largely driven by the technical advances in the measurement of U isotope ratios by mass spectrometry with increasing precision over the last decade. A thorough review on the application of the U-decay series systems within Earth sciences was published in Reviews in Mineralogy and Geochemistry (RiMG) volume 52 in 2003, and will not be discussed further within this review. Instead, this article will first focus on the basic chemical properties of U and the evolution of 238U/235U measurement techniques, before discussing the latest findings and use of this isotopic system to address questions within geochronology, cosmochemistry and Earth sciences.

M. Paetzel

Papers

Uranium and molybdenum isotope systematics in modern euxinic basins: Case studies from the central Baltic Sea and the Kyllaren fjord (Norway)