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Title: New methods of mass spectrometry based on an Electron Cyclotron Resonance ion source
Authors: Hotchkis, MAC
Josh, M
Waring, CL
Wei, T
Keywords: Mass spectrometry
ECR ion sources
Atomic ions
Carbon 14
Stable isotopes
Issue Date: 5-Dec-2006
Publisher: Australian Institute of Physics
Citation: Hotchkis, M., Josh, M., Waring, C., & Wei, T. (2006). New methods of mass spectrometry based on an Electron Cyclotron Resonance ion source. Paper presented at the Australian Instute of Physics 17th National Congress 2006, Brisbane Convention and Exhibition Centre, Brisbane Australia, Sunday 3 - Friday 8 December 2006. Retrieved from:
Abstract: We are investigating the use of multiply-charged atomic ions for measuring isotopic ratios by mass spectrometry. With multiply-charged ions, molecular interferences are reduced or eliminated, as small molecules generally cannot exist as multiply-charged ions. The Electron Cyclotron Resonance Ion Source (ECRIS) provides a highly efficient means for the production of beams of multiply-charged atomic ions [1]. We have built a compact ECRIS at ANSTO for this work. Applications include the measurement of radiocarbon in small mass samples, as an alternative to Accelerator Mass Spectrometry (AMS). In our method for radiocarbon [3], the same two principles that enable AMS to work are used, but in reverse order. Molecular interferences are eliminated in the first stage of the spectrometer system, by producing high charge state ions directly from an ECRIS. 14N interference is eliminated in the second stage, by converting the beam to negative ions in a charge exchange cell. In another application of the ECRIS, we are using it with a single magnetic sector analyser to determine stable isotopic ratios such as 13C/12C and 18O/16O. Measurements of these and other stable isotopes are widely used in geo- and bio-sciences, where either natural variations are studied or isotopic tracers are used. Conventional isotope ratio mass spectrometers use molecular ions (such as CO2+) to determine such ratios. In our method, 2+ atomic ions are selected, thereby eliminating possible molecular interferences and resolving mass ambiguities that exist with the conventional molecular ion method. [1] R. Geller, Electron Cyclotron Resonance Ion Sources and ECR Plasmas, IOP, Bristol, 1996. [2] R. Middleton, in Proc. First Conf. on Radiocarbon Dating with Accelerators, H.E. Gove (ed.), Rochester, USA, 1978. [3] M.A.C. Hotchkis and T. Wei, 10th International Conference on AMS, Sept 5-10 2005, Berkeley, USA.
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