Chemical attribution of the homemade explosive ETN - Part II: Isotope ratio mass spectrometry analysis of ETN and its precursors

Lindsay McLennan,Alexander Yevdokimov,Peter Schoenmakers,Taylor Busby,Jos van den Elshout,Jimmie Oxley,Arian van Asten,Jorien Schoorl,Antoine van der Heijden,Annemieke Hulsbergen,Karlijn Bezemer,Mattijs Koeberg,Eva de Rijke,Rosanne Hessels,James Smith

doi:10.1016/j.forsciint.2020.110344

Abstract

In this follow-up study the collaboration between two research groups from the USA and the Netherlands was continued to expand the framework of chemical attribution for the homemade explosive erythritol tetranitrate (ETN). Isotope ratio mass spectrometry (IRMS) analysis was performed to predict possible links between ETN samples and its precursors. Carbon, nitrogen, hydrogen and oxygen isotope ratios were determined for a wide variety of precursor sources and for ETN samples that were prepared with selected precursors. The stability of isotope ratios of ETN has been demonstrated for melt-cast samples and two-year old samples, which enables sample comparison of ETN in forensic casework independent of age and appearance. Erythritol and nitric acid (or nitrate salt) are the exclusive donor of carbon and nitrogen atoms in ETN, respectively, and robust linear relationships between precursor and the end-product were observed for these isotopes. This allowed for defining isotopic enrichment ranges for carbon and nitrogen that support the hypothesis that a given erythritol or nitrate precursor was used to synthesize a specific ETN batch. The hydrogen and oxygen atoms in ETN do not originate from one exclusive donor material, making linkage prediction more difficult. However, the large negative enrichments observed for both isotopes do provide powerful information to exclude suspected precursor materials as donor of ETN. Additionally, combing the isotopic data of all elements results in a higher discrimination power for ETN samples and its precursor materials. Combining the findings of our previously reported LC–MS analysis of ETN with this IRMS study is expected to increase the robustness of the forensic comparison even further. The partially nitrated impurities can provide insight on the synthesis conditions while the isotope data contain information on the raw materials used for the production of ETN.

Highlights

Erythritol tetranitrate (ETN) is a nitrate ester homemade explosive (HME) that is gaining popularity among amateurs, criminals, and terrorist bomb makers
We have previously reported a study where two large sample sets of ETN were synthesized independently by two forensic laboratories using different synthesis routes and precursors [3]
This paper builds on our previously reported study, which focused on impurity analysis of partially nitrated erythritol using liquid chromatography-mass spectrometry (LC–MS) analysis, by expanding the framework of chemical attribution for forensic explosives intelligence using isotope ratio mass spectrometry (IRMS) to analyze the isotopic compositions of ETN and its precursors

Summary

Introduction

Erythritol tetranitrate (ETN) is a nitrate ester homemade explosive (HME) that is gaining popularity among amateurs, criminals, and terrorist bomb makers. This paper builds on our previously reported study, which focused on impurity analysis of partially nitrated erythritol using LC–MS analysis, by expanding the framework of chemical attribution for forensic explosives intelligence using IRMS to analyze the isotopic compositions of ETN and its precursors. Expanding the framework of chemical attribution with IRMS analysis could allow for predictions in forensic explosives casework concerning precursor materials that could have been used in the homemade synthesis of ETN.

Precursor materials

ETN synthesis

Data analysis

Á ðn m À

Erythritol isotopic composition and distribution

Á mi Á ðni À

Nitrate precursor

ETN samples

Precursor correlation and isotopic fractionation

Chemical attribution and forensic use

Conclusions

Acknowledgements and Disclaimers