Synthesis and structures of Hexa-peri-hexabenzocoronene-based triptycenes

A series of Hexa-peri-hexabenzocoronene-based triptycenes bearing mono-, di-, or tri-HBC moieties were synthesized from iodotriptycenes. Their structures were determined by NMR, MS spectra, and X-ray analysis. The planar HBC moieties displayed strong deshielding effect to triptycene scaffold, resulting in significant downfield chemical shift of the two methenyl protons. Moreover, the HBC units are well separated in the triptycene scaffold, without quenching the fluorescent properties of each HBC unit.     

Rapid voltammetric determination of nitroaromatic explosives at electrochemically activated carbon-fibre electrodes

The electrochemical behaviour of some nitroaromatic explosives (2,4,6-trinitrotoluene, TNT; 2,6-dinitrotoluene, 2,6-DNT; 2-nitrotoluene, 2-NT; 2-amino-4,6-dinitrotoluene, 2-A-4,6-DNT; 3,5-dinitroaniline, 3,5-DNA; and nitrobenzene, NB) at electrochemically activated carbon-fibre microelectrodes is reported. Electrochemical activation of such electrode material by repeated square-wave (SW) voltammetric scans between 0.0 and +2.6 V versus Ag/AgCl, produced a dramatic increase in the cathodic response from these compounds. This is attributed to the increase of the carbon-fibre surface area, because of its fracture, and the appearance of deep fissures along the main fibre axis into which the nitroaromatic compounds penetrate. Based on the important contribution of adsorption and/or thin layer electrolysis to the total voltammetric response, a SW voltammetric method for rapid detection of nitroaromatic explosives was developed. No interference was found from compounds such as hydrazine, phenolic compounds, carbamates, triazines or surfactants. The limits of detection obtained are approximately 0.03 g mL^–1 for all the nitroaromatic compounds tested. The method was applied for the determination of TNT in water and soil spiked samples; recoveries were higher than 95% in all cases.     

Highly sensitive detection of nitroaromatic explosives using an electrospun nanofibrous sensor based on a novel fluorescent conjugated polymer

An electrospun nanofibrous explosive sensor was first constructed based on a newly developed fluorescent conjugated polymer P containing heteroatom polycyclic units. Electrospinning by doping polymer P as a fluorescent probe in a polystyrene supporting matrix afforded a fluorescence nanofibrous film with unique porous structures, and effectively avoided the aggregation of polymer P. The novel explosive sensor exhibited stable fluorescence property, satisfactory reversibility with less than 5% loss of signal intensity after four quenching–regeneration cycles, and good reproducibility among three batches with a relative standard deviation of 2.8%. Such fabricated sensor also showed remarkable sensitivity toward a series of trace nitroaromatic explosive vapors, including picric acid (parts-per-trillion level) and 2,4,6-trinitrotoluene vapor (parts-per-billion level), as well as good selectivity with less than 10% response to typical interferents. Therefore, the present strategy extends the application of different kinds of conjugated polymers for the construction of optical chemosensors.     

Direct injection of seawater for the analysis of nitroaromatic explosives and their degradation products by micellar electrokinetic chromatography

Practical considerations for the injection and separation of nitroaromatic explosives in seawater sample matrices are discussed. The use of high surfactant concentrations and long electrokinetic injections allows for improved detection limits. Sensitivity was enhanced by two mechanisms, improved stacking at the detector-side of the sample plug and desorption of analyte from the capillary wall by surfactant-containing BGE from the inlet side of the sample plug. Calculated limits of detection (S/N = 3) for analytes prepared in pure seawater were 70–800 ppb with injection times varying from 5 to 100 s.     

Development of imprinted materials for the selective extraction of nitroaromatic explosives

Molecularly imprinted sorbents were synthesized and used as selective extraction sorbents for the analysis of nitroaromatic explosives. Their synthesis by radical polymerization using organic monomers and by sol–gel approach using organosilanes was considered to develop a selective sorbent. The sol–gel approach with phenyltrimethoxysilane (PTMS) as monomer and 2,4-dinitrotoluene (2,4-DNT) as template gave the most promising results. An optimized procedure adapted to the selective treatment of aqueous samples was then developed and applied to various target explosives. For the first time four nitroaromatic compounds were retained on the molecularly imprinted silica (MIS) with extraction recoveries between 29% and 81%, while only low recoveries were obtained on the non-imprinted sorbent, thus highlighting the high degree of selectivity. The MIS was then used for the clean-up of a sample containing motor oil spiked with 2,4-DNT and 2,4,6-trinitrotoluene (2,4,6-TNT). The results were compared with those obtained using a conventional sorbent (Oasis HLB). The cleanest chromatogram obtained using the MIS emphasized the high potential of the MIS as selective sorbent.     

Determination of nitroaromatic explosives in water samples by direct ultrasound-assisted dispersive liquid-liquid microextraction followed by gas chromatography-mass spectrometry

A fast, simple, inexpensive, sensitive, efficient and environmental friendly direct ultrasound-assisted dispersive liquid-liquid microextraction (DUSA-DLLME) procedure has been developed to concentrate five nitroaromatic explosives from water samples prior to quantification by gas chromatography-mass spectrometry (GC-MS). An efficient ultrasonic probe has been used to radiate directly the samples producing very fine emulsions from immiscible liquids. A D-optimal design was used for optimizing the factors and to evaluate their influential upon extraction. The optimum experimental conditions were: sample volume, 10 mL; extraction time, 60 s; cycles, 0.6 s(s⁻¹); power of ultrasound energy, 40% (70 W); and, extractant solvent (chlorobenzene) volume, 20 μL. Under the optimized experimental conditions the method presents good level of repeatability with coefficients of variation under 6% (n = 8; spiking level 10 μg L⁻¹). Calculated calibration curves gave high level of linearity with correlation coefficient values between 0.9949 and 0.9992. Limits of detection were ranged between 0.03 and 0.91 μg L⁻¹. Finally, the proposed method was applied to the analysis of two types of water samples, reservoir and effluent wastewater. The samples were previously analysed and confirmed free of target analytes. At 5 μg L⁻¹ spiking level recovery values ranged between 75 and 96% for reservoir water sample showing that the matrix had a negligible effect upon extraction. However, a noticeable matrix effect (around 50% recovery) was observed for effluent wastewater sample. In order to alleviate this matrix effect, the standard addition calibration method was used for quantitative determination. This calibration method supplied recovery values ranged between 71 and 79%. The same conclusions have been obtained from an uncertainty budget evaluation study.     

超声-气相联合扩散法快速合成ZIF-8用于硝基芳香化合物炸药的传感

三维微孔沸石咪唑基骨架(ZIF-8)纳米晶通过超声-气相联合扩散法快速合成.对该纳米晶进行荧光研究表明,纳米晶对硝基芳香化合物炸药具有良好的荧光淬灭能力.通过建立的Stern-Volmer方程,在1×10-4～8×10-4 mol/L范围内,每种炸药的浓度与纳米晶的荧光淬灭程度呈线性关系.对于2,4,6-三硝基苯酚(T...     

Highly selective synthesis of triptycene o-quinone derivatives and their optical and electrochemical properties

A convenient and efficient method for the selective synthesis of a series of triptycene o-quinone derivatives is described. The triptycene o-quinones, especially the ones containing the methoxy group(s) (electron donor) and the o-quinone group(s) (electron acceptor) simultaneously, show interesting intramolecular CT interactions and electrochemical properties. Moreover, DFT calculations display that introducing a strong electron-donor group into triptycene o-quinone results in an increasing of the HOMO energy level, which subsequently decreases the HOMO-LUMO energy gap.     

Vibrational spectroscopy standoff detection of explosives

Standoff infrared and Raman spectroscopy (SIRS and SRS) detection systems were designed from commercial instrumentation and successfully tested in remote detection of high explosives (HE). The SIRS system was configured by coupling a Fourier-transform infrared interferometer to a gold mirror and detector. The SRS instrument was built by fiber coupling a spectrograph to a reflective telescope. HE samples were detected on stainless steel surfaces as thin films (2–30 μg/cm²) for SIRS experiments and as particles (3–85 mg) for SRS measurements. Nitroaromatic HEs: TNT, DNT, RDX, C4, and Semtex-H and TATP cyclic peroxide homemade explosive were used as targets. For the SIRS experiments, samples were placed at increasing distances and an infrared beam was reflected from the stainless steel surfaces coated with the target chemicals at an angle of ∼180° from surface normal. Stainless steel plates containing TNT and RDX were first characterized for coverage distribution and surface concentration by reflection–absorption infrared spectroscopy. Targets were then placed at the standoff distance and SIRS spectra were collected in active reflectance mode. Limits of detection (LOD) were determined for all distances measured for the target HE. LOD values of 18 and 20 μg/cm² were obtained for TNT and RDX, respectively, for the SIR longest standoff distance measured. For SRS experiments, as low as 3 mg of TNT and RDX were detected at 7 m source–target distance employing 488 and 514.5 nm excitation wavelengths. The first detection and quantification study of the important formulation C4 is reported. Detection limits as function of laser powers and acquisition times and at a standoff distance of 7 m were obtained.     

Electrochemical detection of ultratrace nitroaromatic explosives using ordered mesoporous carbon

A sensitive electrochemical sensor has been fabricated to detect ultratrace nitroaromatic explosives using ordered mesoporus carbon (OMC). OMC was synthesized and characterized by scanning electron microscopy, transmission electron microscopy and nitrogen adsorption/desorption measurements. Glassy carbon electrodes functionalized with OMC show high sensitivity of 62.7 μA cm⁻² per ppb towards 2,4,6-trinitrotoluene (TNT). By comparison with other materials such as carbon nanotubes and ordered mesoporous silica, it is found that the high performance of OMC toward sensing TNT is attributed to its large specific surface area and fast electron transfer capability. As low as 0.2 ppb TNT, 1 ppb 2,4-dinitrotoluene and 1 ppb 1,3-dinitrobenzene can be detected on OMC based electrodes. This work renders new opportunities to detect ultratrace explosives for applications of environment protections and home securities against chemical warfare agents.     

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     

A quantitative assessment of chemical techniques for detecting traces of explosives at counter-terrorist portals

Previous reviews have discussed in a qualitative manner the various highly sensitive analytical techniques for detecting minute traces of explosive material. However, there is no review available which compares quantitatively the sensitivities of the different analytical methods for detecting explosives. In view of the importance of this area to the present day planning of counter-terrorist strategies, this review makes a comprehensive and quantitative comparison of the analytical chemical methods which can be used for the detection of trace explosives in the luggage and on the persons of travelers. Possible directions of future development in this area are also discussed.     

Recent advances in fluorescence sensor for the detection of peroxide explosives

The detection of peroxide explosives (PEs) has attracted considerable attention all over the world in global security owing to their simple preparation, poor chemical stability and easy decomposition. In recent years, great efforts have been devoted to developing organic fluorescence sensors for detecting the PEs because of their fast response, high sensitivity and high selectivity. In this short review, we firstly discuss the sensing mechanisms for fluorescence based the PEs detection. Next, we reviewed recent progress of PE probes in the nearly 5 years and the design strategies of the material structures to enhance the sensitivity or selectivity, such as conjugated polymers and assembled nanoparticles.     

CdSe quantum dots capped PAMAM dendrimer nanocomposites for sensing nitroaromatic compounds

The detection of nitroaromatic compounds, best known as raw materials in explosives preparations, is important in many fields including environmental science, public security and forensics. CdSe quantum dots capped with PAMAM-G₄ dendrimer were synthetized in water and used for the detection of trace amounts of three nitroaromatic compounds: 4-methoxy-2-nitrophenol (MNP), 2-amine-5-chloro-1,3-dinitrobenzene (ACNB) and 3-methoxy-4-nitrobenzoic acid (MNB). To increase the apparent water solubility of these compounds α-cyclodextrin (α-CD) was used to promote the formation of inclusion complexes. The studied nitroaromatic compounds (plus α-CD) significantly quenched the fluorescence intensity of the nanocomposite with linear Stern-Volmer plots. The Stern-Volmer constants (standard deviation in parenthesis) were: MNB, K_SV = 65(5) × 10⁴ M⁻¹; ACNB, K_SV = 19(2) × 10⁴ M⁻¹; and, MNP, K_SV = 33(1) × 10² M⁻¹. These constants suggest the formation of a ground state complex between the nitroaromatric compounds and the sensor which confers a relatively high analytical sensitivity. The detection sensibilities are about 0.01 mg L⁻¹ for MNB and ACNB and about 0.1 mg L⁻¹ for MNP. No interferences or small interferences are observed for trinitrotoluene [K_SV = 10(2) × 10² × M⁻¹], 2,4-dinitrotoluene [K_SV = 20(3) × 10 M⁻¹], 2,6-dinitrotoluene [K_SV = 11(4) × 10 M⁻¹] and nitrobenzene [K_SV = 2(1) × 10³ × M⁻¹].     

A three-dimensionally adjustable amperometric detector for microchip electrophoretic measurement of nitroaromatic pollutants

A microchip capillary electrophoresis (CE)–amperometric detection (AD) system has been fabricated by integrating a two-dimensionally adjustable CE microchip and an amperometric detection cell containing a one-dimensionally adjustable disc detection electrode in a Plexiglas holder. It facilitates the precise three-dimensional alignment between the channel outlet and the detection electrode without a complicated three-dimensional manipulator. The performance of this unique system was demonstrated by separating four nitroaromatic pollutants (nitrobenzene, 2,4-dinitrotoluene, 2,4,6-trinitrotoluene, and p-nitrobenzene). Factors influencing their separation and detection processes were examined and optimised. The four analytes have been well-separated within 120 s in a 75 cm long separation channel at a separation voltage of +2000 V using an electrophoretic separation medium containing 15 mM borax and 15 mM sodium dodecyl sulfate (pH 9.2). Highly linear response is obtained for the four analytes over the range of 0–5 ppm with the detection limits ranging from 12 to 52 ppb. The present system demonstrated long-term stability and reproducibility with relative standard deviations of less than 5% for the peak current (n = 9). The new approach for the microchannel–electrode alignment should find a wide range of applications in other microfluidic analysis systems.     

Simultaneous determination of nitroaromatic compounds in water using capillary electrophoresis with amperometric detection on an electrode modified with a mesoporous nano‐structured carbon material

In this article, a carbon disk electrode modified with mesoporous carbon material (CMK‐3) was used in CE with amperometric detection system for the simultaneous determination of four types of important nitroaromatic compounds, including 2,4,6‐trinitrotoluene (TNT), 1,3,5‐trinitrobenzene (TNB), 2,4‐dinitrotoluene (DNT) and 1,3‐dinitrobenzene (DNB). Compared with the bare carbon electrode, the CMK‐3 modified electrode greatly improved the sensitivity at a relatively positive detection potential due to its excellent electrocatalytic activities, high conductivity and large effective surface area. The four analytes could be well separated and detected within 480 s. A good linear response was obtained for TNB, DNB, TNT and DNT from 8.4 to 5.0×10³ μg/L, with correlation coefficients higher than 0.9992. And the detection limits were established between 3.0 and 4.7 μg/L for the four investigated nitroaromatic compounds (S/N=3). The CMK‐3‐modified electrode was successfully employed to analyze coking wastewater, tap water and river samples with recoveries in the range of 94.8–109.0%, and RSDs less than 5.0%. The presented results demonstrated that the CMK‐3‐modified carbon electrode used in CE with amperometric detection was of convenient preparation, high sensitivity and good repeatability, which could be employed in the rapid determination of practical samples.     

Rapid detection of nitroaromatic and nitramine explosives on chromatographic paper and their reflectometric sensing on PVC tablets

Rapid and inexpensive sensing of explosive traces in soil and post-blast debris for environmental and criminological purposes with optical sensors has recently gained importance. The developed sensing method for nitro-aromatic and nitramine-based explosives is based on dropping an acetone solution of the analyte to an adsorbent surface, letting the solvent to dry, spraying an analytical reagent to produce a persistent spot, and indirectly measuring its reflectance by means of a miniature spectrometer. This method proved to be useful for on-site determination of nitro-aromatics (trinitrotoluene (TNT), 2,4,6-trinitrophenylmethylnitramine (tetryl) and dinitrotoluene (DNT)) and nitramines (1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)) pre-adsorbed on a poly vinyl chloride (PVC) surface, with the use of different spray reagents for each group of explosives producing different colors. The calibration equations of the tested compounds as reflectance vs. concentration showed excellent linearity (correlation coefficient: 0.998-0.999). The linear quantification interval in terms of absolute quantity of analyte was 0.1-0.5 μg. The developed method was successfully tested for the analysis of military explosives Comp B and Octol, and was validated against high performance liquid chromatography (HPLC). The reflectometric sensing method could also be used for qualitative identification of the nitrated explosives on a chromatographic paper. The reagent-impregnated paper could also serve as sensor, enabling semi-quantitative determinations of TNT and tetryl.     

Direct detection of explosives on solid surfaces by mass spectrometry with an ambient ion source based on dielectric barrier discharge

Trace amounts of explosives on solid surfaces were detected by mass spectrometry at ambient conditions with a new technique termed dielectric barrier discharge ionization (DBDI). By the needle-plate discharge mode, a plasma discharge with energetic electrons was generated, which could launch the desorption and ionization of the explosives from solid surfaces. Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,4,6-trinitrotoluene (TNT), and pentaerythritol tetranitrate (PETN) were desorbed directly from the explosives-contaminated surface by DBDI, forming the typical anions of [TNT](-), [TNT - H](-), [RDX + NO(2)](-), [PETN + ONO(2)](-), and [RDX + ONO(2)](-). The ions were transferred into the MS instrument for analysis in the negative ion mode. The detection limit of present method was 10 pg for TNT (m/z 197, S/N 8 : 1), 0.1 ng for RDX (m/z 284, S/N 10 : 1), and 1 ng for PETN (m/z 260, S/N 12 : 1). The present method allowed the detection of trace explosives on various matrices, including paper, cloth, chemical fiber, glass, paints, and soil. A relative standard deviation of 5.57% was achieved by depositing 100 pg of TNT on these matrices. The analysis of A-5, a mixture of RDX and additives, has been carried out and the results were consistent with the reference values. The DBDI-MS method represents a simple and rapid way for the detection of explosives with high sensitivity and specificity, which is especially useful when they are present in trace amounts on ordinary environmental surfaces.     

Investigation of common fluorophores for the detection of nitrated explosives by fluorescence quenching

This study assessed the impact of fruit temperature on the phenolic metabolism of grape berries (Vitis vinifera L. cv. Merlot) grown under field conditions with controlled exposure to sunlight. Individual cluster temperatures were manipulated in situ. Diurnal temperature fluctuation was damped by daytime cooling and nighttime heating of clusters. Daytime-only and nighttime-only temperature controls were applied for comparison. Berry temperatures were recorded continuously to compare the chemical data. Samples collected at véraison indicated that damping the diurnal temperature fluctuation advanced the onset of ripening. Those berries were larger (double-damped: 0.753 ± 0.015 g berry⁻¹ vs control: 0.512 ± 0.034 g berry⁻¹) and more colored than all others. Development of phenolic metabolites was followed by two reversed-phase high performance liquid chromatography methods and gel permeation chromatography. These methods provided information on anthocyanins, proanthocyanidins, flavonols, flavan-3-ol monomers, and polymeric material. Damping the diurnal temperature fluctuation reduced proanthocyanidin mean degree of polymerization (double-damped: 21.8 ± 1.0 vs control: 28.0 ± 1.7). Proanthocyanidin accumulation at véraison was linearly related to heat summation over the developmental period with nighttime heating yielding the highest concentration and daytime cooling yielding the lowest (night-heat: 1.46 ± 0.13 mg berry⁻¹ vs day-cool: 0.97 ± 0.09 mg berry⁻¹). Damping the diurnal temperature fluctuation had a marked effect on the rate of fruit development whereas total heat summation had more of an effect on phenolic metabolism alone. The results provide insight on the direct effect of temperature on phenolic metabolism.     

Theoretical evaluation of sensitivity and thermal stability for high explosives based on quantum chemistry methods: A brief review

Over the past 20 years, a number of scientists have conducted numerous fundamental investigations based on quantum chemistry theory into various mechanistic processes that seems to contribute to the sensitivity of energetic materials. A large number of theoretical methods that have been used to predict their mechanical and spark sensitivity are summarized in this article, in which the advantages and disadvantages of these methods, together with their scope of use are clarified. In addition, the theoretical models for thermal stability of explosives are briefly introduced as a supplement. It has been concluded that the current ability to predict sensitivity is merely based on a series of empirical rules, such as simple oxygen balance, molecular properties, and the ratios of C and H to oxygen for different classes of explosive compounds. These are valid only for organic classes of explosives, though some special models have been proposed for inorganic explosives, such as azides. An exact standard for sensitivity should be established experimentally by some new techniques for both energetic compounds and their mixtures. © 2013 Wiley Periodicals, Inc.