Forensic application of position-specific isotopic analysis of trinitrotoluene (TNT) by NMR to determine 13C and 15N intramolecular isotopic profiles

Valentin Joubert; Virginie Silvestre; Virginie Ladroue; Fabrice Besacier; Paule Blondel; Serge Akoka; Evelyne Baguet; Gérald S Remaud

doi:10.1016/j.talanta.2020.120819

Forensic application of position-specific isotopic analysis of trinitrotoluene (TNT) by NMR to determine ¹³C and ¹⁵N intramolecular isotopic profiles

Talanta. 2020 Jun 1:213:120819. doi: 10.1016/j.talanta.2020.120819. Epub 2020 Feb 13.

Authors

Valentin Joubert¹, Virginie Silvestre¹, Virginie Ladroue², Fabrice Besacier², Paule Blondel², Serge Akoka¹, Evelyne Baguet¹, Gérald S Remaud³

Affiliations

¹ Elucidation of Biosynthesis by Isotopic Spectrometry Group, CEISAM, University of Nantes, CNRS UMR6230, F-44322, Nantes, France.
² Institut National de Police Scientifique, Laboratoire de Lyon, 31 avenue Franklin Roosevelt, 69134, Ecully Cedex, France.
³ Elucidation of Biosynthesis by Isotopic Spectrometry Group, CEISAM, University of Nantes, CNRS UMR6230, F-44322, Nantes, France. Electronic address: gerald.remaud@univ-nantes.fr.

PMID: 32200922
DOI: 10.1016/j.talanta.2020.120819

Abstract

2,4,6-trinitrotoluene (TNT) is a molecule which is easily identified with current instrumental techniques but it is generally impossible to distinguish between sources of the same substance (TNT). To overcome this difficulty, we present a multi stable isotope approach using isotope ratio monitoring by mass spectrometry (irm-MS) and Nuclear Magnetic Resonance spectrometry (irm-NMR). In the one hand, irm-MS provides bulk isotopic composition at natural abundance in ¹³C and ¹⁵N. The range of variation between samples is rather small particularly for ¹³C. In the other hand, irm-¹³C NMR and irm-¹⁵N NMR enable the determination of positional intramolecular ¹³C/¹²C ratios (δ¹³C_i) and ¹⁵N/¹⁴N ratios (δ¹⁵N_i) with high precision that lead to larger variation between samples. The present work reports an application of the recent methodology using irm-¹⁵N NMR to determine position-specific ¹⁵N isotope content of TNT. The interest of this methodology is compared to irm-¹³C NMR and irm-MS (¹³C and ¹⁵N) in terms of TNT samples discrimination. Thanks to the use of irm-NMR the results show a unique isotopic fingerprint for each TNT which enable origin discrimination between the samples without ambiguity.

Keywords: 2,4,6-Trinitrotoluene; Explosives; Irm-(13)C NMR; Irm-(15)N NMR; PSIA.