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Natural processes, from cosmochemistry to human homeostasis, can be traced by means of the mass-dependent fractionation of K isotopes because the 39K/41K ratio is characterized by a wide range of variations (ca. 3‰). The measurement of the 39K/41K ratio is traditionally achieved by multi-collector inductively coupled plasma mass spectrometers (MC-ICPMS), but is significantly impeded by large isobaric argide interferences on K isotopes. A new generation of MC-ICPMS equipped with a collision/reaction cell allows the quantitative elimination of argide interferences using H2 as a reaction gas. We report on a set of high-precision K isotopic data obtained with the recently released ThermoScientific Neoma MC-ICPMS/MS equipped with a prefiltering system consisting of a double-Wien filter and a collision/reaction cell. In the low-resolution mode, the mass resolving power is ca. 2200, resulting in a K sensitivity of ca. 1000 V ppm-1 for 39K in dry mode with an Apex Omega desolvator. This large mass revolving power allows the observation of yet undetected interferences on the high-mass shoulders of 39K and 41K. The interference is ca. 25 mV on 39K and 1 mV on 41K in the low-resolution mode, similar in K and blank HNO3 (0.05 M) solutions, increases when N2 is added in the desolvator and decreases when He is added as a collision gas. The presence of these interferences, which contribute modestly < 0.02% of the K signal, is probably the result of the formation of complex organic compounds in the collision/reaction cell. However, blank subtraction is a critical step to achieve steady and accurate analysis of the 39K/41K ratio. The overall stability of the analysis of the 39K/41K ratio is greatly improved by using a continuous-flow microFAST Isotope autosampler. A survey on the potential effects of sample-standard mismatches reveals significant offsets for matrix elements (Ca, Mg and Na), no offset for acid molarity. Regarding the effect of sample-standard concentration mismatch, we show that the amplitude of the offset is session-dependent, such that no general correction could be applied. We use the autosampler adjustable injection flow rate to correct for a concentration mismatch up to ± 30% to recover expected K isotope composition within the ± 0.05‰ uncertainty. In these conditions, short-term external precision and long-term reproducibility are 0.07‰ (2SD, n = 500) and 0.08‰ (2SD, n = 66), respectively. For validation of the overall method, we finally purified K using a single step chemical separation by ion exchange chromatography, and measured the K isotope composition of geological and biological reference materials, for which we found values similar to the literature. Our study shows that the Neoma MC-ICPMS/MS with continuous flow injection is a robust instrumentation that will contribute to expediting high-precision K isotopic measurements for various applications. [ABSTRACT FROM AUTHOR]

The new Neoma MC-ICPMS/MS is equipped with a prefiltering system consisting of a double-Wien filter and a collision/reaction cell whose performances are challenged using different combinations of magnetic and electrostatic field values and adjustable slit apertures. The results show an asymmetrical attenuation of transmission relative to the chosen axial mass-to-charge value, with higher efficiency at removing low masses than high masses, even when magnetic induction is minimal. The resulting asymmetry of the bandpass window is fully predictable by theoretical calculations of ion trajectories in a Wien filter, either as a function of the magnetic field value or that of the aperture of the adjustable slit. With an axial mass-to-charge value set at 120Sn, the vertical deviation for a magnetic field value at 100% will be approximately 3 mm and 4 mm for a variation of mass-to-charge of ±20%, respectively. In these conditions, Ar was already barely detectable with the lowest magnetic field value (10%) and a fully open adjustable slit, while Pb is quantitatively transmitted. We then use the prefiltering system to remove on-line the 40Ar23Na+ compound that produces an isobaric interference with 63Cu, hampering high-precision measurement of Cu stable isotope composition (65Cu/63Cu). While Na is not transmitted thanks to the double-Wien filter, 40Ar23Na+ still interferes with 63Cu, demonstrating that this argide is produced in the plasma source but not in the reaction cell. Helium in the collision/reaction cell is necessary to remove the 40Ar23Na+ interference. The MS/MS technology of the Neoma allows for the correction of the 40Ar23Na+ interference up to a Na/Cu ratio of 10, where other classic MC-ICPMS already show an offset of the Cu stable isotope composition for a Na/Cu ratio of 1. The inability to correct the Cu stable isotope composition with a Na/Cu ratio higher than 10 suggests that the Na-based interference is no longer spectral and becomes linked to the matrix. We next measure the Cu stable isotope composition in eight certified reference materials prepared with a simple automated single step ion-chromatography procedure to purify Cu. The results show a very good agreement with previously reported values. The overall results suggest that the MS/MS technology of the Neoma MC-ICPMS allows efficient on-line isolation of analytes, therefore reducing potential spectral and matrix interferences to permit much better resolved and controlled subsequent effects in the collision/reaction cell. [ABSTRACT FROM AUTHOR]

The notion of a dry Moon has recently been challenged by the discovery of high water contents in lunar apatites and in melt inclusions within olivine crystals from two pyroclastic glasses. The highest and most compelling water contents were found in pyroclastic glasses that are not very common on the lunar surface. To obtain more representative constraints on the volatile content of the lunar interior, we measured the Zn content, a moderately volatile element, of mineral and rock fragments in lunar soils collected during Apollo missions. We here confirm that the Moon is significantly more depleted in Zn than the Earth. Combining Zn with existing K and Rb data on similar rocks allows us to anchor a new volatility scale based on the bond energy of nonsiderophile elements in their condensed phases. Extrapolating the volatility curve to H shows that the bulk of the lunar interior must be dry (≤1 ppm). This contrasts with the water content of the mantle sources of pyroclastic glasses, inferred to contain up to approximately 40 ppm water based on H2O/Ce ratios. These observations are best reconciled if the pyroclastic glasses derive from localized water-rich heterogeneities in a dominantly dry lunar interior. We argue that, although late addition of 0.015% of a chondritic veneer to the Moon seems required to explain the abundance of platinum group elements (Day et al. 2007), the volatile content of the added material was clearly heterogeneous. [ABSTRACT FROM AUTHOR]

Hereditary hemochromatosis is a genetic iron overload disease related to a mutation within the HFE gene that controls the expression of hepcidin, the master regulator of systemic iron metabolism. The natural stable iron isotope composition in whole blood of control subjects is different from that of hemochromatosis patients and is sensitive to the amount of total iron removed by the phlebotomy treatment. The use of stable isotopes to unravel the pathological mechanisms of iron overload diseases is promising but hampered by the lack of data in organs involved in the iron metabolism. Here, we use H fe -/- mice, a model of hereditary hemochromatosis, to study the impact of the knock-out on iron isotope compositions of erythrocytes, spleen and liver. Iron concentration increases in liver and red blood cells of H fe -/- mice compared to controls. The iron stable isotope composition also increases in liver and erythrocytes, consistent with a preferential accumulation of iron heavy isotopes in H fe -/- mice. In contrast, no difference in the iron concentration nor isotope composition is observed in spleen of H fe -/- and control mice. Our results in mice suggest that the observed increase of whole blood isotope composition in hemochromatosis human patients does not originate from, but is aggravated by, bloodletting. The subsequent rapid increase of whole blood iron isotope composition of treated hemochromatosis patients is rather due to the release of hepatic heavy isotope-enriched iron than augmented iron dietary absorption. Further research is required to uncover the iron light isotope component that needs to balance the accumulation of hepatic iron heavy isotope, and to better understand the iron isotope fractionation associated to metabolism dysregulation during hereditary hemochromatosis., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Albalat, Cavey, Leroyer, Ropert, Balter and Loréal.)