Isotopic and elemental profiling of ammonium nitrate in forensic explosives investigations Hanneke Brust a,b,c, *, Mattijs Koeberg b , Antoine van der Heijden c,d , Wim Wiarda b , Ines Mu ¨ gler b,1 , Marianne Schrader b , Gabriel Vivo-Truyols a , Peter Schoenmakers a , Arian van Asten a,b,e a University of Amsterdam, van ’t Hoff Institute for Molecular Sciences, PO Box 94157, 1090 GD Amsterdam, The Netherlands b Netherlands Forensic Institute, PO Box 24044, 2490 AA The Hague, The Netherlands c TNO Defence, Security and Safety, PO Box 45, 2280 AA Rijswijk, The Netherlands d Delft University of Technology, PO Box 5, 2600 AA Delft, The Netherlands e CLHC, Amsterdam Center for Forensic Science and Medicine, PO Box 94157, 1090 GD Amsterdam, The Netherlands 1. Introduction Ammonium nitrate (AN) has applications in explosives in industry, such as mining and civil construction [1,2]. Its chemical stability and low sensitivity to shock and friction [1,3,4] make it relatively safe to produce and to handle in large quantities. Combined with its low costs these properties make AN a suitable ingredient for explosive devices. Explosive-grade ammonium nitrate generally exists in the form of slurries, emulsions, or porous prills mixed with a fuel (ammonium nitrate fuel oil, ANFO) [1]. Obtaining explosive-grade AN for criminal abuse is difficult due to extensive regulations, but AN in the form of fertilizer prills or granules is widely available [1,3,4]. The European Commission prohibits the distribution of ammonium nitrate-containing ferti- lizers with a nitrogen percentage higher than 16% to private parties [5]. In addition, detonation tests should be performed on fertilizers with a nitrogen content of more than 28% [6]. Fertilizer prills have a higher density and a lower porosity than explosive-grade prills, reducing the sensitivity to detonate. However, fertilizer-grade ammonium nitrate can still detonate or be made to detonate [3,4]. Besides industrial applications of AN-based explosives, terrorist attacks involving the use of AN in improvised explosive devices (IEDs) have been a concern for many years. Afghanistan and Iraq are countries with a large number of attacks with AN-based IEDs, due to its low costs and ease of implementation. Forensic Science International 248 (2015) 101–112 A R T I C L E I N F O Article history: Received 3 July 2014 Received in revised form 22 November 2014 Accepted 27 November 2014 Available online 8 December 2014 Keywords: Ammonium nitrate Isotope-ratio mass spectrometry (laser ablation–) inductively coupled plasma–mass spectrometry Explosive Chemical profiling Likelihood ratios A B S T R A C T Ammonium nitrate (AN) is frequently encountered in explosives in forensic casework. It is widely available as fertilizer and easy to implement in explosive devices, for example by mixing it with a fuel. Forensic profiling methods to determine whether material found on a crime scene and material retrieved from a suspect arise from the same source are becoming increasingly important. In this work, we have explored the possibility of using isotopic and elemental profiling to discriminate between different batches of AN. Variations within a production batch, between different batches from the same manufacturer, and between batches from different manufacturers were studied using a total of 103 samples from 19 different fertilizer manufacturers. Isotope-ratio mass spectrometry (IRMS) was used to analyze AN samples for their 15 N and 18 O isotopic composition. The trace-elemental composition of these samples was studied using inductively coupled plasma–mass spectrometry (ICP–MS). All samples were analyzed for the occurrence of 66 elements. 32 of these elements were useful for the differentiation of AN samples. These include magnesium (Mg), calcium (Ca), iron (Fe) and strontium (Sr). Samples with a similar elemental profile may be differentiated based on their isotopic composition. Linear discriminant analysis (LDA) was used to calculate likelihood ratios and demonstrated the power of combining elemental and isotopic profiling for discrimination between different sources of AN. ß 2014 Elsevier Ireland Ltd. All rights reserved. * Corresponding author: Tel.: +31 613679924. E-mail addresses: hannekebrust@gmail.com (H. Brust), m.koeberg@nfi.minvenj.nl (M. Koeberg), antoine.vanderheijden@tno.nl (A. van der Heijden), w.wiarda@nfi.minvenj.nl (W. Wiarda), m.schrader@nfi.minvenj.nl (M. Schrader), g.vivotruyols@uva.nl (G. Vivo-Truyols), p.j.schoenmakers@uva.nl (P. Schoenmakers), a.van.asten@nfi.minvenj.nl (A. van Asten). 1 Present address: University of Hamburg, Centre for Earth System Research and Sustainability, Grindelberg 5, 20144 Hamburg, Germany. Contents lists available at ScienceDirect Forensic Science International jou r nal h o mep age: w ww.els evier .co m/lo c ate/fo r sc iin t http://dx.doi.org/10.1016/j.forsciint.2014.11.024 0379-0738/ß 2014 Elsevier Ireland Ltd. All rights reserved.