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

摘要

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 C-13 and (15N). The range of variation between samples is rather small particularly for C-13. In the other hand, irm-C-13 NMR and irm-N-15 NMR enable the determination of positional intramolecular C-13/C-12 ratios (delta C-13(i)) and N-15/N-14 ratios (delta N-15(i)) with high precision that lead to larger variation between samples. The present work reports an application of the recent methodology using irm-N-15 NMR to determine position-specific N-15 isotope content of TNT. The interest of this methodology is compared to irm-C-13 NMR and irm-MS (C-13 and N-15) 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.