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

In this work, a reliable and robust vacuum-​outlet gas chromatog.-​mass spectrometry (GC-​MS) method is introduced for the identification and quantification of impurities in trinitrotoluene (TNT)​. Vacuum-​outlet GC-​MS allows for short anal. times; the anal. 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 compds. showed to be useful for discrimination between TNT samples from different sources. Statistical anal. of these impurity profiles using likelihood ratios demonstrated the potential to investigating whether two questioned TNT samples encountered in forensic casework are from the same source.