Assessment of portable FTIR and Raman spectroscopy for the detection of 2,3-dimethyl-2,3-dinitrobutane (DMDNB) in plastic explosives

Abstract

The Marplex Convention was established to prevent the manufacture of unmarked plastic explosives and stipulates that a volatile detection agent must be added at the time of manufacture. However, to-date, laboratory testing remains the internationally accepted practice for identifying and quantifying the taggants stipulated in the Convention. In this project, portable FTIR and Raman instruments were tested for their ability to detect 2,3-dimethyl-2,3-dinitrobutane (DMDNB), the chemical marker incorporated in plastic explosives that are manufactured within Australia. While both FTIR and Raman instruments detected solid DMDNB (98% purity), field analysis of plastic explosives at an Australian Defence establishment showed that both FTIR and Raman spectra were matched the relevant explosive (RDX or PETN), rather than the DMDNB taggant. For all three plastic explosives tested, the concentration of DMDNB was measured by SPME-GC-MS to be between 1.8 and 2%, greater than the minimum 1% concentration stipulated by the Marplex Convention. Additional testing with a plastic explosive analogue confirmed that the minor absorption peaks that would characterize low concentrations of DMDNB were masked by absorption bands from other compounds within the solid. Thus, while both FTIR and Raman spectroscopy are suitable for detection of plastic explosives, neither rely on the presence of DMDNB for detection. It is likely that similar results would be found for other taggants stipulated by the Marplex Convention, given they are also present in concentrations less than 1%.