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

• NCJ Number: 229705
• Journal: Journal of Forensic Sciences Volume: 55 Issue: 1 Dated: January 2010 Pages: 193-204
• Author(s): Sarah J. Benson, Ph.D.; Christopher J. Lennard, Ph.D.; David M. Hill, B.Sc.; Philip Maynard, Ph.D.; Claude Roux, Ph.D.
• Date Published: January 2010
• Length: 12 pages
• Publication Format: Article
• Publication Type: Report (Study/Research)
• Language: English
• Country: United States of America
• Note: For Part 2 of this two-part article, see NCJ-229706.

Annotation

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.

Abstract

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 FlashEAtm 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 percent) and ammonium thiocyanate (99.99+percent) 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. 10 tables, 12 figures, 27 references, and appendix (Published abstract)