Search

The development of instruments and methods for explosive vapor detection is a continually evolving field of interest. A thorough understanding of the characteristic vapor signatures of explosive material is imperative for the development and testing of new and current detectors. In this research a headspace sampling chamber was designed to contain explosive materials for the controlled, reproducible sampling and characterization of vapors associated with these materials. In a detonation test, the chamber was shown to contain an explosion equivalent to three grams of trinitrotoluene (TNT) without damage to the chamber. The efficacy of the chamber in controlled headspace sampling was evaluated in laboratory tests with bulk explosive materials. Small quantities of TNT, triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) were separately placed in the sampling chamber, and the headspace of each material was analyzed by gas chromatography/mass spectrometry (GC/MS) with online cryogenic trapping to yield characteristic vapor signatures for each explosive compound. Chamber sampling conditions, temperature and sampling time, were varied to demonstrate suitability for precise headspace analysis. [ABSTRACT FROM AUTHOR]

This note describes the design of a simple, wire-array ion gate that is easy to create and machine. The gate consists of two separate wires that can be pulsed differentially to either neutralize ions or deflect the path of an ion beam. Unlike previous designs, the gate described herein consists of only a single piece: an insulator through which two wires are woven to create an interdigitated array. The wires are then terminated at both ends, where electrical connections to external voltage sources can be made. Once constructed, the gate has a 1 mm grid spacing and takes about 3–4 h to complete after the initial support is machined. A gate constructed with this design has been successfully installed in an ion-mobility spectrometer, and its performance compares favorably to that of a previously configured gate system. [ABSTRACT FROM AUTHOR]

Abstract: A simple method for establishing calibration curves with sorbent-filled thermal desorption tubes has been demonstrated for nitroaromatic and nitramine vapor samples using a thermal desorption system with a cooled inlet system (TDS–CIS), which was coupled to a gas chromatograph (GC) with an electron capture detector (ECD). The method relies upon the direct liquid deposition of standard solutions onto the glass frit at the head of sorbent-filled thermal desorption tubes. Linear calibration results and ideal system conditions for the TDS–CIS–GC–ECD were established for mixtures containing both cyclotrimethylenetrinitramine, a.k.a. RDX, and 2,4,6-trinitrotoluene (TNT). Because of the chemical characteristics of RDX, a higher TDS–CIS flow rate relative to the optimized approach for TNT was required for efficient RDX desorption. Simultaneous quantitation of TNT and RDX using the direct liquid deposition method with optimized instrumentation parameters for RDX were compared to results from a standard split/splitless GC inlet and a CIS. [Copyright &y& Elsevier]

Abstract: The use of thermal desorption systems for the analysis of trace vapors typically requires establishing a calibration curve from vapors generated with a permeation tube. The slow equilibration time of permeation tubes causes such an approach to become laborious when covering a wide dynamic range. Furthermore, many analytes of interest, such as explosives, are not available as permeation tubes. A method for easily and effectively establishing calibration curves for explosive vapor samples via direct deposition of standard solutions on thermal desorption tubes was investigated. The various components of the thermal desorption system were compared to a standard split/splitless inlet. Calibration curves using the direct liquid deposition method with a thermal desorption unit coupled to a cryo-focusing inlet were compared to a standard split/splitless inlet, and a statistical difference was observed but does not eliminate or deter the use of the direct liquid deposition method for obtaining quantitative results for explosive vapors. [Copyright &y& Elsevier]

A novel vapor delivery testbed, referred to as the Trace Explosives Sensor Testbed, or TESTbed, is demonstrated that is amenable to both high- and low-volatility explosives vapors including nitromethane, nitroglycerine, ethylene glycol dinitrate, triacetone triperoxide, 2,4,6-trinitrotoluene, pentaerythritol tetranitrate, and hexahydro-1,3,5-trinitro-1,3,5-triazine. The TESTbed incorporates a six-port dual-line manifold system allowing for rapid actuation between a dedicated clean air source and a trace explosives vapor source. Explosives and explosives-related vapors can be sourced through a number of means including gas cylinders, permeation tube ovens, dynamic headspace chambers, and a Pneumatically Modulated Liquid Delivery System coupled to a perfluoroalkoxy total-consumption microflow nebulizer. Key features of the TESTbed include continuous and pulseless control of trace vapor concentrations with wide dynamic range of concentration generation, six sampling ports with reproducible vapor profile outputs, limited low-volatility explosives adsorption to the manifold surface, temperature and humidity control of the vapor stream, and a graphical user interface for system operation and testing protocol implementation. [ABSTRACT FROM AUTHOR]

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 billionvolume (ppbv) to parts per trillionvolume (pptrv) 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 µ-ECD detector. With 30 min sample times and an average sampling rate of 100 mL min-1, vapor concentrations of 38 pptrv for TNT, 25 pptrvfor RDX, and 26 pptrv for PETN were determined. For parts per quadrillionvolume (ppqv) 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 ppqv and 710 ppqv for TNT and RDX were quantified, respectively, with an instrument duty cycle as low as 4 min. [ABSTRACT FROM AUTHOR]

An analytical method for establishing calibration curves for the quantitation of pentaerythriol tetranitrate (PETN) from sorbent-filled thermal desorption tubes by gas chromatography with electron capture detection (TDS-GC-ECD) was developed. As PETN has been demonstrated to thermally degrade under typical GC instrument conditions, peaks corresponding to both PETN degradants and molecular PETN are observed. The retention time corresponding to intact PETN was verified by high-resolution mass spectrometry with a flowing atmospheric pressure afterglow (FAPA) ionization source, which enabled soft ionization of intact PETN eluting the GC and subsequent accurate-mass identification. The GC separation parameters were transferred to a conventional GC-ECD instrument where analytical method-induced PETN degradation was further characterized and minimized. A method calibration curve was established by direct liquid deposition of PETN standard solutions onto the glass frit at the head of sorbent-filled thermal desorption tubes. Two local, linear relationships between detector response and PETN concentration were observed, with a total dynamic range of 0.25–25 ng. [ABSTRACT FROM AUTHOR]

Current and emerging capabilities of plasma-source mass spectrometry (PS-MS) as it is employed for elemental speciation analysis are reviewed. Fundamental concepts and their advantageous aspects, experimental conditions, and analytical performance are described and illustrated by recent examples from the literature. Novel instrumentation, techniques, and strategies for inductively-coupled plasma mass spectrometry (ICP-MS), microwave-induced plasma (MIP) mass spectrometry, glow-discharge (GD) mass spectrometry, and electrospray ionization (ESI), among others, are described. The use of ionization sources that provide tunable ionization, others that can be modulated between different sets of operating conditions, and others used in parallel is also examined. [Copyright &y& Elsevier]