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Forensic Analysis of Explosives Using Isotope Ratio Mass Spectrometry (IRMS)—Part 1: Instrument Validation of the DELTAplusXP IRMS for Bulk Nitrogen Isotope Ratio Measurements

Authors

  • Sarah J. Benson Ph.D.,

    1. Forensic & Data Centres, Australian Federal Police, GPO Box 401, Canberra, ACT 2601, Australia.
    2. Centre for Forensic Science, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007, Australia.
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  • Christopher J. Lennard Ph.D.,

    1. Forensic & Data Centres, Australian Federal Police, GPO Box 401, Canberra, ACT 2601, Australia.
    2. National Centre for Forensic Studies, University of Canberra, Canberra, ACT 2601, Australia.
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  • David M. Hill B.Sc.,

    1. Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234, Australia.
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  • Philip Maynard Ph.D.,

    1. Centre for Forensic Science, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007, Australia.
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  • Claude Roux Ph.D.

    1. Centre for Forensic Science, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007, Australia.
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Additional information and reprint requests:
Sarah Jane Benson, Ph.D.
Australian Federal Police
GPO Box 401
Canberra
ACT 2601
Australia
E-mail: sarah.benson@afp.gov.au

Abstract

Abstract:  A significant amount of research has been conducted into the use of stable isotopes to assist in determining the origin of various materials. The research conducted in the forensic field shows the potential of isotope ratio mass spectrometry (IRMS) to provide a level of discrimination not achievable utilizing traditional forensic techniques. Despite the research there have been few, if any, publications addressing the validation and measurement uncertainty of the technique for forensic applications. This study, the first in a planned series, presents validation data for the measurement of bulk nitrogen isotope ratios in ammonium nitrate (AN) using the DELTAplusXP (Thermo Finnigan) IRMS instrument equipped with a ConFlo III interface and FlashEA™ 1112 elemental analyzer (EA). Appropriate laboratory standards, analytical methods and correction calculations were developed and evaluated. A validation protocol was developed in line with the guidelines provided by the National Association of Testing Authorities, Australia (NATA). Performance characteristics including: accuracy, precision/repeatability, reproducibility/ruggedness, robustness, linear range, and measurement uncertainty were evaluated for the measurement of nitrogen isotope ratios in AN. AN (99.5%) and ammonium thiocyanate (99.99+%) were determined to be the most suitable laboratory standards and were calibrated against international standards (certified reference materials). All performance characteristics were within an acceptable range when potential uncertainties, including the manufacturer’s uncertainty of the technique and standards, were taken into account. The experiments described in this article could be used as a model for validation of other instruments for similar purposes. Later studies in this series will address the more general issue of demonstrating that the IRMS technique is scientifically sound and fit-for-purpose in the forensic explosives analysis field.

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