Fate dynamics of environmentally exposed explosive traces

The chemical and physical fates of trace amounts (<50 μg) of explosives containing 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and pentaerythritol tetranitrate (PETN) were determined for the purpose of informing the capabilities of tactical trace explosive detection systems. From these measurements, it was found that the mass decreases and the chemical composition changes on a time scale of hours, with the loss mechanism due to a combination of sublimation and photodegradation. The rates for these processes were dependent on the explosive composition, as well as on both the ambient temperature and the size distribution of the explosive particulates. From these results, a persistence model was developed and applied to model the time dependence of both the mass and areal coverage of the fingerprints, resulting in a predictive capability for determining fingerprint fate. Chemical analysis confirmed that sublimation rates for TNT were depressed by UV (330-400 nm) exposure due to photochemically driven increases in the molecular weight, whereas the opposite was observed for RDX. No changes were observed for PETN upon exposure to UV radiation, and this was attributed to its low UV absorbance.     

Optimized thermal desorption for improved sensitivity in trace explosives detection by ion mobility spectrometry

In this work we evaluate the influence of thermal desorber temperature on the analytical response of a swipe-based thermal desorption ion mobility spectrometer (IMS) for detection of trace explosives. IMS response for several common high explosives ranging from 0.1 ng to 100 ng was measured over a thermal desorber temperature range from 60 °C to 280 °C. Most of the explosives examined demonstrated a well-defined maximum IMS signal response at a temperature slightly below the melting point. Optimal temperatures, giving the highest IMS peak intensity, were 80 °C for trinitrotoluene (TNT), 100 °C for pentaerythritol tetranitrate (PETN), 160 °C for cyclotrimethylenetrinitramine (RDX) and 200 °C for cyclotetramethylenetetranitramine (HMX). By modifying the desorber temperature, we were able to increase cumulative IMS signal by a factor of 5 for TNT and HMX, and by a factor of 10 for RDX and PETN. Similar signal enhancements were observed for the same compounds formulated as plastic-bonded explosives (Composition 4 (C-4), Detasheet, and Semtex). In addition, mixtures of the explosives exhibited similar enhancements in analyte peak intensities. The increases in sensitivity were obtained at the expense of increased analysis times of up to 20 seconds. A slow sample heating rate as well as slower vapor-phase analyte introduction rate caused by low-temperature desorption enhanced the analytical sensitivity of individual explosives, plastic-bonded explosives, and explosives mixtures by IMS. Several possible mechanisms that can affect IMS signal response were investigated such as thermal degradation of the analytes, ionization efficiency, competitive ionization from background, and aerosol emission.     

Fast gas chromatography-differential mobility spectrometry of explosives from TATP to Tetryl without gas atmosphere modifiers

Explosives in solution were determined as mixtures containing highly volatile improvised explosives such as peroxides and conventional military grade explosives such as PETN, RDX, and Tetryl using a high speed gas chromatograph with differential mobility detector in a single measurement. Instrument parameters were evaluated and adjusted to permit detection of nanogram amounts of explosives with this broad range of vapor pressures in times under 3 min for HMTD to TNT or under 16 min for HMTD to Tetryl. As in prior studies of response to explosives with mobility spectrometers, pre-separation of sample by gas chromatography improved response in the differential mobility detector; however, unlike prior configurations, the supporting gas atmosphere did not contain modifiers to adjust selectivity in mobility and selectivity was provided only by characteristic stability of product ions in negative and positive polarities. Field dependence of product ions in purified air was determined for each explosive and patterns were sufficiently distinct to suggest the addition of selectivity through the use of several differential mobility detectors operated in parallel or series with characteristic separation voltages.     

气相色谱-质谱联用辅助鉴定细菌内毒素标准品菌种来源的纯度

为分析内毒素标准品菌种来源的纯度,建立了采用气相色谱-质谱联用法、以N,O-双三甲基硅三氟乙酰胺作为硅烷化试剂对待测物进行衍生、对内毒素标准品所含的3-羟基脂肪酸种类进行检测的方法。色谱柱为DB-5 (60 m×0.25 mm i.d.);载气为氦气,恒压,柱前压206 kPa;进样器温度250 ℃;柱箱初始温度为90 ℃,保持5 min,以5 ℃/min的升温速率升至280 ℃,保持5 min。进样量为1 μL,不分流进样。质谱离子源为电子轰击离子源（EI）,离子源温度为250 ℃,接口温度为280 ℃。通过对内毒素标准品和大肠杆菌、绿脓杆菌、去离子水中3-羟基脂肪酸种类的比较,探讨了通过3-羟基脂肪酸种类来辅助判断内毒素标准品菌种来源的问题。结果显示,来源为大肠杆菌的9000 EU/支内毒素国家标准品中只含有3-羟基十四烷酸;20 EU/支的内毒素工作标准品中除含有3-羟基十四烷酸外,还含有3-羟基十二烷酸,说明其含有非大肠杆菌的细菌。     

Photofragmentation of nitro-based explosives with chemiluminescence detection

A simple, fast, reliable, sensitive and potentially portable explosive detection device was developed employing laser photofragmentation (PF) followed by heterogeneous chemiluminescence (CL) detection. The PF process involves the release of NO_{x(x = 1,2)} moieties from explosive compounds such as TNT, RDX, and PETN through a stepwise excitation–dissociation process using a 193 nm ArF laser. The NO_{x(x = 1,2)} produced upon PF is subsequently detected by its CL reaction with basic luminol solution. The intensity of the CL signal was detected by a thermoelectrically cooled photomultiplier tube with high quantum efficiency and negligible dark current counts. The system was able to detect trace amounts of explosives in various forms in real time under ambient conditions. Detection limits of 3 ppbv for PETN, 2 ppbv for RDX, and 34 ppbv for TNT were obtained. It was also demonstrated that the presence of PETN residue within the range of 61 to 186 ng/cm² can be detected at a given signal-to-background ratio of 10 using a few microjoules of laser energy. The technique also demonstrated its potential for the direct analysis of trace explosive in soil. An LOD range of 0.5–4.3 ppm for PETN was established, which is comparable to currently available techniques. Figure Photofragmentation–chemiluminescence detector     

Micro structural investigations on TNT and PETN incorporated silica xerogels

Silica xerogels incorporated with trinitrotoluene (TNT) and pentaerythritoltetranitrate (PETN) were synthesized using sol–gel method. Tetramethoxysilane was used as precursor for silica. TNT and PETN content in the resulted explosive/silica xerogel was varied ranging from 50 to 90%. Infra red spectra showed that explosives were retained in the silica xerogel matrix. Transmission electron microscopy (TEM) reveal that explosives particles were uniformly distributed in xerogel matrix and the size of the PETN and TNT particles are in the range 15–18 nm. Small angle x-ray scattering showed that the sizes of the pores in the silica matrix are in the range 25–13 nm. The particles of TNT and PETN occupy the pores in the matrix resulting in gradual reduction of pore-size affecting the surface characteristics of the pore-matrix interface. Understanding of the structure of aggregates of small particles thus produced could be useful to explain the properties shown by the fine explosives. Our study suggests that particle size of explosives in the nanometer range can be achieved using the sol–gel method.     

Negative-Ion formation in the explosives RDX,PETN, and TNT by using the reversal electron attachment detection technique

First results of a beam-beam, single-collision study of negative-ion mass spectra produced by attachment of zero-energy electrons to the molecules of the explosives RDX, PETN, and TNT are presented. The technique used is reversal electron attachment detection (READ) wherein the zero-energy electrons are produced by focusing an intense electron beam into a shaped electrostatic field which reverses the trajectory of electrons. The target beam is introduced at the reversal point, and attachment occurs because the electrons have essentially zero longitudinal and radial velocity. The READ technique is used to obtain the “signature” of molecular ion formation and/or fragmentation for each explosive. Present data are compared with results from atmospheric-pressure ionization and negative-ion chemical ionization methods.     

Detection of explosives on skin using ambient ionization mass spectrometry

Single nanogram amounts of the explosives TNT, RDX, HMX, PETN and their mixtures were detected and identified in a few seconds on the surface of human skin without any sample preparation by desorption electrospray ionization (DESI) using a spray solution of methanol-water doped with sodium chloride to form the chloride adducts with RDX, HMX, and PETN while TNT was examined as the radical anion and tandem mass spectrometry was used to confirm the identifications.     

Orthogonal Detection of Nitroaromatic Explosives via Direct Voltammetry Coupled to Enzyme‐Mediated Biocatalysis

This article describes a rapid and reliable electrochemical/enzymatic method of verifying the presence of nitroaromatic explosives. The new technique leverages both conventional voltammetric analysis and biocatalytic conversion of TNT. The simultaneous use of independent measurement schemes, based on two distinct processes, dramatically increases the information content and offers substantially improved reliability while minimizing the occurrence of false alarms. This has been accomplished by coupling direct voltammetric analysis with the biocatalytic conversion of the TNT substrate via nitroreductase (NR), which reduces a nitro group of TNT using NADH as an electron donor. This chemical reduction (30 s timescale) can then be observed using square‐wave voltammetry by examination of the reductive and oxidative features. This novel protocol was found to be selective for TNT, not only when compared to DNT and NT, but also to other explosive species such as RDX and PETN. This unique dual‐mode detection strategy for measuring TNT at a single device holds considerable promise for improving the probability of explosive detection and hence for diverse security screening applications.     

Secondary electrospray ionization (SESI) of ambient vapors for explosive detection at concentrations below parts per trillion

We determine the sensitivity of several commercial atmospheric pressure ionization mass spectrometers towards ambient vapors, ionized by contact with an electrospray of acidified or ammoniated solvent, a technique often referred to as secondary electrospray ionization (SESI). Although a record limit of detection of 0.2 × 10⁻¹² atmospheres (0.2 ppt) is found for explosives such as PETN and 0.4 ppt for TNT (without preconcentration), this still implies the need for some 10⁸–10⁹ vapor molecules/s for positive identification of explosives. This extremely inefficient use of sample is partly due to low charging probability (∼10⁻⁴), finite ion transmission, and counting probability in the mass spectrometer (1/10 in quadrupoles), and a variable combination of duty cycle and background noise responsible typically for a 10³ factor loss of useful signal.     

单向气流负电晕放电离子迁移谱的研究及其在爆炸物检测中的应用

基于离子迁移谱的爆炸物探测仪多采用放射性电离源,发展非放射性电离源一直是该技术的研究热点。本研究基于电晕放电原理设计了一种新型负电晕放电电离源结构,结合自行研制的离子迁移谱仪,应用于痕量爆炸物的快速、高灵敏检测。单向气流模式下,对此电离源的气流、放电电压等运行参数进行了系统优化,得到最佳实验条件为：电晕放电电离源结构的电极环孔直径为3 mm,针-环距离为2 mm,放电电压为2400 V,漂气流速为1200 mL/min。在此条件下,避免了放电副产物氮氧化物和臭氧等引发的一系列复杂反应,得到了单一的反应试剂离子O-2(H2O)n。将其应用于爆炸物,如2,4,6-三硝基甲苯(TNT)、硝酸铵(AN)、硝化甘油( NG)、太安( PETN)、黑索金( RDX)等的高灵敏快速直接检测,对TNT的检测限达到200 pg/μL。结果表明,此负电晕放电电离源具有灵敏度高、结构简单、无辐射性、反应试剂离子单一等优点,在爆炸物快速高灵敏检测、公共安全保障等方面具有广阔的应用前景。     

Rapid Estimation of Thermodynamic Parameters and Vapor Pressures of Volatile Materials at Nanoscale

Non‐isothermal measurements of thermodynamic parameters and vapor pressures of low‐volatile materials are favored when time is a crucial factor to be considered, such as in the case of detection of hazardous materials. In this article, we demonstrate that optical absorbance spectroscopy can be used non‐isothermally to estimate the thermodynamic properties and vapor pressures of volatile materials with good accuracy. This is the first method to determine such parameters in nanoscale in just minutes. Trinitrotoluene (TNT) is chosen because of its low melting temperature, which makes it impossible to determine its thermodynamic parameter by other rising‐temperature techniques, such as thermogravimetric analysis (TGA). The well‐characterized vapor pressure of benzoic acid is used to calibrate the spectrometer in order to determine the vapor pressure of low‐volatile TNT. The estimated thermodynamic properties of both benzoic acid and TNT are in excellent agreement with the literature. The estimated vapor pressure of TNT is one order of magnitude larger than that determined isothermally using the same method. However, the values are still within the range reported in the literature. The data indicate the high potential for use of rising‐temperature absorbance spectroscopy in determining vapor pressures of materials at nanometer scale in minutes instead of hours or days.     

Separation of HT and HTO in the atmosphere with porous Vycor glass tube

The continuous selective monitoring of tritium gas (HT) in the air containing HT and tritiated water vapor (HTO) was investigated by using the separation cell made of porous Vycor glass tube. On admitting the air containing HT or HTO into the separation cell, HT permeated immediately through the Vycor tube depending on the partial pressure, however, HTO permeated very slowly through the Vycor tube after initial induction period. The initial induction period was elongated with a rise of the temperature of separation cell and then the permeability of HTO decreased remarkably. In the air containing HT and water vapor, the permeation of HT through the Vycor tube was considerably restricted by the water vapor adsorbed on the Vycor tube at lower temperature (at 25 degrees C) but it was hardly affected by water vapor at higher temperature (greater than 50 degrees C) since water vapor was difficult to adsorb on the Vycor tube. These results indicated that HT in the air containing HT and water vapor can be continuously monitored by using the separation cell made of the porous Vycor glass tube.     

Analysis of 2,4,6-trinitrotoluene, pentaerythritol tetranitrate and cyclo-1,3,5-trimethylene-2,4,6-trinitramine using negative corona discharge ion mobility spectrometry

In this study, the capability of negative corona discharge ion mobility spectrometry (IMS) for quantitative magnitude of several explosives including 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN) and cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) has been evaluated for the first time. The total current obtained with the negative corona discharge was about 100 times larger than that of IMS based on ⁶³Ni, which results in a lower detection limit and a wider linear dynamic range. The detection limits for PETN, TNT and RDX were 8×10⁻¹¹, 7×10⁻¹¹ and 3×10⁻¹⁰ g, respectively. The calibration plots for these explosives showed linear dynamic ranges of about four orders of magnitude.     

Construction and characterization of a high-flow, high-resolution ion mobility spectrometer for detection of explosives after personnel portal sampling

A novel analysis of explosives via the coupling of an airline passenger personnel portal with a high-flow (HF), high-resolution (HR) ion mobility spectrometry (IMS) was shown for the first time. The HF-HR-IMS utilized a novel ion aperture grid design with a (63)Ni ionization source while operating at ambient pressure in the positive ion mode at 200 degrees C. The HF-HR-IMS response characteristics of 2,4,6-trinitrotoluene (TNT), 4,6-dinitro-o-cresol (4,6DNOC), and cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) were investigated. Modifications made to the HF-HR-IMS exhaust and ionization source created an 800% increase in the total ion current (TIC), from 0.85 to 6.8 nA. This translated into a 65% ion response increase for TNT when compared with a traditional IMS. A mixture of TNT and (4,6DNOC) was used to successfully demonstrate the resolving power of the species with similar reduced mobility constants (K(o)), 1.54 and 1.59, respectively. The reactant ion (H(2)O)(n)H(+), peak was also used to measure the resolving power of the spectrometer while varying the internal diameter of three different aperture openings from 1.00 to 3.54cm. This provided a resolving power range of 50-60, double that typically achievable by commercial IMS instruments. Most important, these changes made in this new instrumental design can be implemented to all existing and future IMS's to greatly enhance the achievable IMS resolving power.     

Low-mass ions observed in plasma desorption mass spectrometry of high explosives

The low-mass ions observed in both positive and negative plasma desorption mass spectrometry (PDMS) of the high explosives HMX, RDX, CL-20, NC, PETN and TNT are reported. Possible identities of the most abundant ions are suggested and their presence or absence in the different spectra is related to the properties of the explosives as matrices in PDMS. The detection of abundant NO+ and NO2- ions for HMX, RDX and CL-20, which are efficient matrices, indicates that explosive decomposition takes place in PDMS of these three substances and that a contribution from the corresponding chemical energy release is possible. The observation of abundant C2H4N+ and CH2N+ ions, which have high protonation properties, might also explain the higher protein charge states observed with these matrices. Also, the observation of NO2-, possibly formed by electron scavenging which increases the survival probability of positively charged protein molecular ions, completes the pattern. TNT does not give any of these ions and it is thereby possible to explain why it does not work as a PDMS matrix. For NC and PETN, decomposition does not seem to be as pronounced as for HMX, RDX and CL-20, and also no particularly abundant ions with high protonation properties are observed. The fact that NC works well as a matrix might be related to other properties of this compound, such as its high adsorption ability.     

Predicting Trigger Bonds in Explosive Materials through Wiberg Bond Index Analysis

Understanding the explosive decomposition pathways of high‐energy‐density materials (HEDMs) is important for developing compounds with improved properties. Rapid reaction rates make the detonation mechanisms of HEDMs difficult to understand, so computational tools are used to predict trigger bonds—weak bonds that break, leading to detonation. Wiberg bond indices (WBIs) have been used to compare bond densities in HEDMs to reference molecules to provide a relative scale for the bond strength to predict the activated bonds most likely to break to trigger an explosion. This analysis confirms that X?NO₂ (X=N,C,O) bonds are trigger linkages in common HEDMs such as TNT, RDX and PETN, consistent with previous experimental and theoretical studies. Calculations on a small test set of substituted tetrazoles show that the assignment of the trigger bond depends upon the functionality of the material and that the relative weakening of the bond correlates with experimental impact sensitivities.     

Sensitive analysis of alkyl alcohols as decomposition products of alkyl nitrites in human whole blood and urine by headspace capillary GC with cryogenic oven trapping

The abuse of alkyl nitrites is becoming a serious social problem worldwide. In this report, a simple and sensitive method is presented for the determination of n-butyl alcohol, isobutyl alcohol, and isoamyl alcohol as decomposition products of alkyl nitrites in human whole blood and urine samples using capillary gas chromatography (GC) with cryogenic oven trapping. After heating a whole blood or urine sample containing each alkyl alcohol and t-butyl alcohol [the internal standard (IS)] in a 7-mL vial at 55 degrees C for 15 min, 5 mL of the headspace vapor is drawn into a gas-tight syringe and injected into a GC inlet port. The vapor is introduced into an Rtx-BAC2 medium-bore capillary column in the splitless mode at 0 degrees C oven temperature in order to trap the entire analytes, and then the oven temperature is programmed up to 240 degrees C for the GC measurements by flame ionization detection. These conditions give sharp peaks for each compound and the IS and low background noise for whole blood or urine samples. The detection limits of the analytes are 10 ng/mL for whole blood and 5 ng/mL for urine. Linearity and precision are also tested to confirm the reliability of this method. Isobutyl alcohol and methemoglobin could be determined from the whole blood samples of three male volunteers who had sniffed isobutyl nitrite.     

Quantitative thermodynamic analysis of sublimation rates using an atomic force microscope

Atomic force microscopy (AFM) has been successfully used to study the activation energy for evaporation of pentaerythritol tetranitrate (PETN) nanoislands formed by spin coating. These islands are annealed isothermally in the temperature range of 30-70 degrees C for a given time and are scanned with AFM in contact mode at room temperature. The volume of these islands does not change significantly up to about 35-40 degrees C indicating that sublimation is not significant below 40 degrees C. Above 40 degrees C, the islands start shrinking, and the rate of weight loss is analyzed as a function of temperature. The activation energy of evaporation using AFM was found to be similar to that for bulk PETN crystals using thermogravimetric analysis (TGA) at higher temperatures (110-135 degrees C). These results demonstrate that AFM is a useful tool to measure thermodynamic properties with a nanoscale probe.