TECHNICAL NOTE CRIMINALISTICS Sarah J. Benson, 1,2 Ph.D.; Christopher J. Lennard, 1,3 Ph.D.; Philip Maynard, 2 Ph.D.; David M. Hill, 4 B.Sc.; Anita S. Andrew, 5 Ph.D.; Ken Neal, 6 B.Sc.; Hilary Stuart-Williams, 7 Ph.D.; Janet Hope, 8 B.Sc.; G. Stewart Walker, 9 Ph.D.; and Claude Roux, 2 Ph.D. Forensic Analysis of Explosives Using Isotope Ratio Mass Spectrometry (IRMS)—Part 2: Forensic Inter-Laboratory Trial: Bulk Carbon and Nitrogen Stable Isotopes in a Range of Chemical Compounds (Australia and New Zealand) ABSTRACT: Comparability of data over time and between laboratories is a key issue for consideration in the development of global databases, and more broadly for quality assurance in general. One mechanism that can be utilized for evaluating traceability is an inter-laboratory trial. This paper addresses an inter-laboratory trial conducted across a number of Australian and New Zealand isotope ratio mass spectrometry (IRMS) laborato- ries. The main objective of this trial was to determine whether IRMS laboratories in these countries would record comparable values for the distrib- uted samples. Four carbon containing and four nitrogen containing compounds were distributed to seven laboratories in Australia and one in New Zealand. The laboratories were requested to analyze the samples using their standard procedures. The data from each laboratory was evaluated collec- tively using International Standard ISO 13528 (Statistical methods for use in proficiency testing by inter-laboratory comparisons). ‘‘Warning signals’’ were raised against one participant in this trial. ‘‘Action signals’’ requiring corrective action were raised against four participants. These participants reviewed the data and possible sources for the discrepancies. This inter-laboratory trial was successful in providing an initial snapshot of the potential for traceability between the participating laboratories. The statistical methods described in this article could be used as a model for others needing to evaluate stable isotope results derived from multiple laboratories, e.g., inter-laboratory trials ⁄ proficiency testing. Ongoing trials will be conducted to improve traceability across the Australian and New Zealand IRMS community. KEYWORDS: forensic science, isotope ratio mass spectrometry, inter-laboratory trial, traceability, nitrogen isotope, carbon isotope, isotope ratios The potential for the isotope ratio mass spectrometry (IRMS) technique to be utilized in the forensic field to assist in identifying the source of a variety of evidence types (e.g., explosives and illicit drugs) is well recognized and has recently been reviewed (1). Given the relatively short history of use of IRMS in the forensic science industry, the technique requires validation for a range of applications prior to casework implementation. One aspect of the technique requiring validation is traceability—the comparability of results obtained by different laboratories and at different times (2). In order to evaluate traceability in the Australian and New Zealand IRMS community, an inter-laboratory trial was organized. Samples were prepared and distributed to a number of Australian and New Zealand IRMS laboratories. A number of international inter-labora- tory trials have been conducted, including those by the FIRMS Network (3–5); however, it was deemed necessary to conduct a locally based trial as the laboratories in the region would be the ones most likely to exchange data and share databases. The primary objective of this inter-laboratory trial was to deter- mine whether IRMS laboratories in Australia and New Zealand would report comparable values for the distributed samples. A sec- ondary objective was to assist in determining the true stable isotope values for laboratory standards for use in the Australian Federal Police laboratory for the determination of bulk nitrogen and carbon isotope ratios. Additionally, the compilation of details of methodol- ogy used in each laboratory would provide data to recommend best 1 Forensic & Data Centres, Australian Federal Police, GPO Box 401, Canberra 2601, ACT, Australia. 2 Centre for Forensic Science, University of Technology, Sydney, PO Box 123, Broadway 2007, NSW, Australia. 3 National Centre for Forensic Studies, University of Canberra, Canberra 2601, ACT, Australia. 4 Australian Nuclear Science and Technology Organisation, PMB 1, Menai 2234, NSW, Australia. 5 Environmental Isotopes Pty. Ltd., PO Box 1492, Macquarie Centre 2113, NSW, Australia. 6 Iso-trace Ltd., Centre for Innovation, St David Street, Dunedin, New Zealand. 7 Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra 2601, ACT, Australia. 8 Geoscience Australia, GPO Box 378, Canberra 2601, ACT, Australia. 9 School of Chemistry, Physics and Earth Sciences, Flinders University, GPO 2100, Adelaide 5001, SA, Australia. Received 6 Oct. 2007; and in revised form 17 May 2008; accepted 24 Jan. 2009. J Forensic Sci, January 2010, Vol. 55, No. 1 doi: 10.1111/j.1556-4029.2009.01242.x Available online at: interscience.wiley.com Ó 2009 American Academy of Forensic Sciences 205