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Isotopic and elemental profiling of ammonium nitrate in forensic explosives investigations

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Author: Brust, H. · Koeberg, M. · Heijden, A. van der · Wiarda, W. · Mügler, I. · Schrader, M. · Vivo-Truyols, G. · Schoenmakers, P. · Asten, A. van
Type:article
Date:2015
Publisher: Elsevier Ireland Ltd
Source:Forensic Science International, 248, 101-112
Identifier: 522500
doi: doi:10.1016/j.forsciint.2014.11.024
Keywords: (laser ablation-) inductively coupled plasma-mass spectrometry · Ammonium nitrate · Chemical profiling · Explosive · Isotope-ratio mass spectrometry · Likelihood ratios · Ammonium nitrate · Calcium · Fertilizer · Iron · Isotope · Magnesium · Nitrogen · Oxygen · Strontium · Analytic method · Chemical composition · Controlled study · Crime · Discriminant analysis · Isotope ratio mass spectrometry · Isotopic and elemental profiling · Mass spectrometry · Defence, Safety and Security · Fluid Mechanics Chemistry & Energetics · EM - Energetic Materials · TS - Technical Sciences

Abstract

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 15N and 18O 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.