RESUMO
The coupling of an atmospheric pressure ionization source (Direct Analysis in Real Time, DART) and a high-resolution mass spectrometer (Orbitrap) has enabled the rapid and efficient analysis of a variety of energetic formulations. This approach was used to generate mass spectra for 83 plastic explosives and polymer samples in less than 2 min per sample. To manually interpret and identify all of the constituent polymers and other interesting features in the acquired mass spectra is a tedious and time-consuming challenge. Instead, a methodology based on the systematic calculation of Kendrick mass defects (KMDs) was developed and implemented. Its application allowed the identification of the polymeric support present in each energetic formulation. The presence of polyisobutylene in PG2 has been confirmed thanks to this approach, and a mixture of polyisobutylene, polybutadiene, and polystyrene has been confirmed in the Semtex 10 formulation. The developed methodology has also permitted the observation of changes that occur to the polymeric composition of these formulations after a blast. It appears that the most adequate way to describe post blast polymer samples is that they are less oxygenated and, above all, more unsaturated than the original starting material. These conclusions were deduced with the aid of principal component analysis, which served to establish the main factors that differentiate the samples.
RESUMO
Fluorinated polymers are a diverse and important class of polymers with unique applications. However, characterization of fluorinated polymers by conventional mass spectrometric methods is challenging because (i) their high fluorine contents make them insoluble or only sparingly soluble in most common solvents and (ii) commonly used matrices employed for MALDI do not desorb or ionize them efficiently. In this work, atmospheric-solid-analysis-probe (ASAP) high-resolution orbitrap mass spectrometry (HRMS) was used as a new tool for the molecular characterization of various fluorinated polymers, including polyvinylidene fluoride (PVDF) and fluorinated copolymers containing PVDF and chlorotrifluoroethylene (KEL-F 800) or PVDF and hexafluoropropylene (Viton A and Tecnoflon). The major peaks of the observed distributions were assigned compositions, but the high number of species required the use of an alternative method to treat such complex data. Kendrick-mass defects (KMD) were calculated on the basis of the "common-to-all" vinylidene difluoride repeating unit. By plotting the KMD as a function of the nominal Kendrick masses (NKM), specific patterns based on homologous series emerged. Kendrick maps were therefore drawn to simplify the mass spectra and provide confident peak assignments through homologous-series recognition. A specific fingerprint for each polymer has been identified, and the ability to discern the four species present in a blend through KMD analysis was demonstrated.
RESUMO
The development of rapid, efficient, and reliable detection methods for the characterization of energetic compounds is of high importance to security forces concerned with terrorist threats. With a mass spectrometric approach, characteristic ions can be produced by attaching anions to analyte molecules in the negative ion mode of electrospray ionization mass spectrometry (ESI-MS). Under optimized conditions, formed anionic adducts can be detected with higher sensitivities as compared with the deprotonated molecules. Fundamental aspects pertaining to the formation of anionic adducts of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), 1,3,5-trinitro-1,3,5-triazinane (RDX), pentaerythritol tetranitrate (PETN), nitroglycerin (NG), and 1,3,5-trinitroso-1,3,5-triazinane energetic (R-salt) compounds using various anions have been systematically studied by ESI-MS and ESI tandem mass spectrometry (collision-induced dissociation) experiments. Bracketing method results show that the gas-phase acidities of PETN, RDX, and HMX fall between those of HF and acetic acid. Moreover, PETN and RDX are each less acidic than HMX in the gas phase. Nitroglycerin was found to be the most acidic among the nitrogen-rich explosives studied. The ensemble of bracketing results allows the construction of the following ranking of gas-phase acidities: PETN (1530-1458 kJ/mol) > RDX (approximately 1458 kJ/mol) > HMX (approximately 1433 kJ/mol) > nitroglycerin (1427-1327.8 kJ/mol).
