Impurity profiling of trinitrotoluene using vacuum-outlet gas chromatography–mass spectrometry

• Vacuum-outlet GC–MS for fast analysis of the explosive trinitrotoluene.
• Identification and quantification of impurities in trinitrotoluene.
• Trinitrotoluene from different sources can be discriminated using impurity profiles.
• Calculation of the evidential value of impurity profiles using likelihood ratios.

In this work, a reliable and robust vacuum-outlet gas chromatography–mass spectrometry (GC–MS) method is introduced for the identification and quantification of impurities in trinitrotoluene (TNT). Vacuum-outlet GC–MS allows for short analysis times; the analysis of impurities in TNT was performed in 4 min. This study shows that impurity profiling of TNT can be used to investigate relations between TNT samples encountered in forensic casework. A wide variety of TNT samples were analyzed with the developed method. Dinitrobenzene, dinitrotoluene, trinitrotoluene and amino-dinitrotoluene isomers were detected at very low levels (<1 wt.%) by applying the MS in selected-ion monitoring (SIM) mode. Limits of detection ranged from 6 ng/mL for 2,6-dinitrotoluene to 43 ng/mL for 4-amino-2,6-dinitrotoluene. Major impurities in TNT were 2,4-dinitrotoluene and 2,3,4-trinitrotoluene. Impurity profiles based on seven compounds showed to be useful to TNT samples from different sources. Statistical analysis of these impurity profiles using likelihood ratios demonstrated the potential to investigate whether two questioned TNT samples encountered in forensic casework are from the same source.