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Published February 1, 2013 | public
Journal Article

A high-resolution gas-source isotope ratio mass spectrometer

Abstract

We describe a new high-resolution, multi-collector gas source mass spectrometer designed for isotopic analysis of volatile and semi-volatile molecules: the Thermo Scientific MAT253-Ultra, a prototype double-focusing isotope ratio mass spectrometer installed in the Caltech laboratories for stable isotope geochemistry. This instrument achieves mass resolving power of up to ∼27,000 (M/ΔM) and can analyze diverse gases and semi-volatile compounds using a conventional dual inlet and/or a carrier gas. It has a multi-collector array comprised of 7 detector positions with adjustable spacing, all of which can register ions through an SEM or Faraday cup and spanning up to a 10^(13) range in signal strength. Abundance sensitivity in the He mass range is as good as 10^(−12), and precision commonly approaches the counting statistics limit down to 0.1‰ (SEM) or 0.01‰ (Faraday) for a range of analytes. This instrument permits resolution of isobaric interferences arising from both contaminants and multiple isotopologues of an analyte that share a cardinal mass, enabling direct isotopic analysis of molecules with complex mass spectra such as hydrocarbons. This ability should enable the measurement of position-specific isotopic compositions, including multiple substitutions, by comparing isotope ratios of molecular ions with those of daughter fragment ions (assuming products of recombination and other source reactions are recognized and corrected for). The combination of high mass resolution with stable multicollection will provide a wide range of potential new tools for isotope geochemistry, including (but not limited to): singly and multiply substituted methane and larger hydrocarbons; position-specific ^(13)C analysis of propane and larger hydrocarbons; precise analysis of ^(17)O/^(16)O and ^(18)O/^(16)O on fragment ions from CO_2 and other molecules; analysis of a variety of N_2O isotopologues (including ^(18)O, ^(17)O, position-specific ^(15)N, and various 'clumped' species); and high precision and abundance sensitivity noble gas analyses. These capabilities greatly extend the scope of stable isotope variations that can be utilized for problems in forensics, environmental geochemistry, biochemistry, and Earth and planetary sciences.

Additional Information

© 2012 Elsevier B.V. Received 24 August 2012. Received in revised form 16 October 2012. Accepted 17 October 2012. Available online 23 October 2012. The Ultra prototype mass spectrometer received partial funding from the NSF-EAR Instruments and Facilities program and from the California Institute of Technology. Some of the illustrative data presented in this paper was generated as part of an applied research project funded by Petrobras. Additional funding to support components of this work came from an NSF Graduate Fellowship and postdoctoral fellowship funding from the California Institute of Technology. We thank Nami Kitchen for assistance in the laboratories for stable isotope geochemistry at Caltech, and the staff at Thermo Scientific, including Chuck Douthitt, Frank Heine, Thomas Heise, Andreas Hilkert, and Silke Seedorf, for their commitment to the construction of the Ultra. We thank Ken Farley for providing samples of helium analyzed as part of this study.

Additional details

Created:
August 22, 2023
Modified:
October 23, 2023