Trace Explosives Vapor Generation and Quantitation at Parts per Quadrillion Concentrations

摘要

The generation of trace 2,4,6 -trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX), and pentaerythritol tetranitrate (PETN) vapors using a pneumatically modulated liquid delivery system (PMLDS) coupled to a polytetrafluoroethylene (PTFE) total-consumption micronebulizer is presented. The vapor generator operates in a continuous manner with final vapor concentrations proportional to the explosive concentration in aqueous solution delivered through the nebulizer and the diluent air flow rate. For quantitation of concentrations in the parts per billion(volume) (ppb(v)) to parts per trillion(volume) (pptr(v)) range, Tenax-TA thermal desorption tubes were used for vapor collection with subsequent analysis on a thermal-desorption system programmable-temperature vaporization gas chromatograph (TDS-PTV-GC) with a mu-ECD detector. With 30 min sample times and an average sampling rate of 100 mL min(-1), vapor concentrations of 38 pptr(v) for TNT, 25 pptr(v) for RDX, and 26 pptr(v) for PETN were determined. For parts per quadrillion(volume) (ppq(v)) vapor quantitation of TNT and RDX, an online PTV-GC system with a negative-ion chemical ionization mass spectrometer (methane reagent gas) was used for direct sampling and capture of the vapor on the PTV inlet. Vapor concentrations as low as 160 ppq(v) and 710 ppq(v) for TNT and RDX were quantified, respectively, with an instrument duty cycle as low as 4 min.