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Identification of Nitro Explosives by Direct Analysis in Real-Time Time-of-Flight Mass Spectrometry

ABSTRACT Nitro compounds such as 2,4,6-trinitrotoluene, cyclotrimethylene trinitramine, and pentaerythritol tetranitrate are common ingredients of high explosives found in homeland security threats, minefields, and industrial materials. This study aims at developing a convenient surface analysis method for rapid identification of these compounds by direct analysis in real time coupled with time-of-flight mass spectrometry. The possible ionization mechanisms and fragmentation pathways using the direct analysis in real-time ionization source were developed for each compound based on the ions produced by in-source collision-induced dissociation and acquired by a time-of-flight mass spectrometer. These compounds release nitro groups and form nitroless characteristic fragments with other nitro adducts during in-source collision-induced dissociation processes. The characteristic ion [M + C2H4N3O2]− produced by cyclotrimethylene trinitramine was observed for the first time to our best knowledge. Direct analysis in real-time time-of-flight mass spectrometry has provided rapid identification of residues from various samples from explosion scenes and, therefore, is a potential powerful screening tool for criminal evidence.