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

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 (δ13Ci) and 15N/14N ratios (δ15Ni) 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.