Fluorescence quenching of CdSe quantum dots by nitroaromatic explosives and their relative compounds

CdSe quantum dots (QDs) were synthesized in oleic acid and octadecene medium under high-temperature and dispersed in chloroform. Nitroaromatic explosives and their relative compounds, 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), nitrobenzene (NB), 2,4-dinitrochlorobenzene (DNBCl) and p-nitrotoluene (NT) can obviously cause the fluorescence quenching of the synthesized QDs. Under the optimum conditions, a nonlinear response was observed over the concentration range of 10(-8) to 10(-5) M for them all. The modified Stern-Volmer quenching equations of ln I(0)/I versus C show a good linear relation in 10(-5) M order of magnitude, and the detection limits approach 10(-6) to 10(-7) M.     

Solid-phase microextraction versus single-drop microextraction for the analysis of nitroaromatic explosives in water samples.

This paper compares solid-phase microextraction (SPME) with a recently developed extraction method called single-drop microextraction (SDME) for the analysis of nitroaromatic explosives in water samples. The two techniques are examined in terms of procedure, chromatographic analysis and method performance. All practical considerations for both techniques are also reviewed. SPME requires dedicated apparatus and is relatively expensive, as the fiber's lifetime is limited. However, it has the advantages over SDME that it can be easily used for headspace analysis and has lower detection limits for all the target analytes. SDME requires more elaborate manual operations, thus affecting linearity and precision.     

Application of solvent microextraction to the analysis of nitroaromatic explosives in water samples

The application of solvent microextraction to the analysis of nitroaromatic explosives is presented. Extraction of 11 nitroaromatics was achieved by suspending 1 microl of organic solvent to the tip of a microsyringe in a stirred aqueous solution. Parameters such as extraction solvent, stirring rate, salt concentration and sampling time were studied and optimized. The limits of detection using bench-top quadrupole mass spectrometry and short extraction times (15 min) were found to be between 0.08 and 1.3 microg/l and the relative standard deviations ranged between 4.3 and 9.8%. Although precision and accuracy of quantification of the method are still needed, solvent microextraction proved to be a fast, simple and inexpensive tool for preconcentration and matrix isolation of nitroaromatics on a microscale.     

Fluorescent metal-organic framework for selective sensing of nitroaromatic explosives

Highly luminescent micrometre-sized fine particles of a Zn(II) metal-organic framework (MOF) of a new π-electron rich tricarboxylate dispersed in ethanol is demonstrated as a selective sensory material for the detection of nitroaromatic explosives via a fluorescence quenching mechanism.     

Femtosecond laser photoionization time-of-flight mass spectrometry of nitro-aromatic explosives and explosives related compounds

The ultrafast laser-induced photoionization and photodissociation processes of the nitroaromatic containing explosive and explosive related compounds (ERCs) nitrobenzene (NB), 1,3-dinitrobenzene (DNB), m-nitrotoluene (MNT), 2,4-dinitrotoluene (DNT), and 2,4,6-trinitrotoluene (TNT) have been investigated at three laser wavelengths and power densities using a time-of-flight mass spectrometer. Examination of the mass spectra of these compounds reveals the enhanced formation of the molecular ion [M⁺] when ultraviolet (332 nm) and visible (495 nm) light is used relative to infrared (795 nm) radiation. In addition, at 795 nm and a power density of 3. 5 × 10¹⁴ W/cm², the presence of a competition between multiphoton ionization (MPI) and Coulomb explosion (CE) channels is revealed by peak shape analysis, and is thought to be operative under these conditions for all of the molecules investigated.     

Voltammetric determination of nitroaromatic and nitramine explosives contamination in soil

The contamination of soil by nitroaromatic and nitramine explosives is widespread during the manufacture, testing and disposal of explosives and ammunitions. The analysis for the presence of trace explosive contaminants in soil becomes important in the light of their effect on the growth of different varieties of plants and crops. 2,4,6-Trinitrotoluene (TNT), cyclotrimethylene trinitramine (Research Department explosive, RDX) and cyclotetramethylene tetranitramine (high melting point explosive, HMX), other related explosive compounds and their by-products must be monitored in soil and surrounding waterways since these are mutagenic, toxic and persistent pollutants that can leach from the contaminated soil to accumulate in the food chain. In this study, a voltammetric method has been developed for the determination of explosive such as RDX, HMX and TNT. The electrochemical redox behavior of RDX, HMX and TNT was studied through cyclic voltammetry and quantitative determination was carried out by using square wave voltammetry technique. Calibration curves were drawn and were linear in the range of 63-129 ppm for RDX with a detection limit of 10 ppm, 49-182 ppm for HMX with a detection limit of 1 ppm and 38-139 ppm for TNT with a detection limit of 1 ppm. This method was applied to determine the contaminations in several soil samples that yielded a relative error of 1% in the concentrations.     

A luminescent nanoscale metal-organic framework for sensing of nitroaromatic explosives

The first nanoscale luminescent metal-organic framework has been realized for the straightforward and highly sensitive sensing of nitroaromatic explosives in enthanol solution.     

Three-dimensional nanographene based on triptycene for detection of nitroaromatic explosives

3D nanographene 1, with three HBC units arraying in the 3D triptycene scaffold, displayed strong intrinsic fluorescence properties and could be used as a detector for nitroaromatic explosives such as TNP with quenching efficiency K_sv of 1.8 × 10⁴ M⁻¹ and sensitivity of 2.4 ng/mm², respectively.     

On-line preconcentration strategies for trace analysis of metabolites by capillary electrophoresis

Analysis of low concentrations of metabolites is required for new fields of biological research, such as metabolomics. In this review, recent work in our laboratory aimed at developing improved strategies for on-line sample preconcentration of metabolites by capillary electrophoresis (CE) is presented. Dynamic pH junction, sweeping and dynamic pH junction-sweeping represent three complementary methods for electrokinetic focusing of large volumes of sample directly on-capillary. Focusing selectivity and focusing efficiency are two factors that can be used to assess the suitability of each method for different classes of metabolites. Buffer properties can be selected to enhance the focusing of specific types of metabolites based on knowledge of the analyte physicochemical properties. The application of on-line preconcentration CE for trace analysis of metabolites in real samples of interest, such as biological fluids and cellular extracts, is also demonstrated. Under optimum conditions, up to three orders of magnitude increase in concentration sensitivity can be realized for several classes of metabolites, including catecholamines, purines, nucleosides, nucleotides, amino acids, steroids and coenzymes. Recent work on hyphenating on-line preconcentration with multiplexed CE is highlighted as a promising platform for sensitive and high-throughput analyses of metabolites.     

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.     

A new luminescent metal-organic framework for selective sensing of nitroaromatic explosives

A microporous luminescent metal-organic framework [Zn_4L_2(H_2O)_2].(H_2O)_m(DMA)_n(1)(H_4L=5,5'-((1H-pyrazole-3,5-dicarbonyl)bis(azanediyl))diisophthalic acid, DMA=N,N-dimethylacetamide) was synthesized and characterized by infrared radiation(IR), thermogravimetric analyses(TGA), powder X-ray diffraction spectra(PXRD) and X-ray diffraction. Complex 1has a three dimensional(3D) framework, which can be simplified as 5,5,5,5-c net with the Schlfi symbol of {43.64.83}{44.65.8}{45.65}2. This luminescent metal-organic framework(MOF) shows selectively sensitive to nitrobenzene and series of nitroaromatic explosives such as 4-nitrotoluene, 1,4-dinitrobenzene, 1,3-dinitrobenzene and 2,4-dinitrotoluene, and exhibits well recyclability. So complex 1 could be used to detect nitroaromatic explosives as a selective sensing material.     

Micellar electrokinetic chromatography and capillary electrochromatography of nitroaromatic explosives in seawater

The ability to separate nitroaromatic and nitramine explosives in seawater sample matrices is demonstrated using both MEKC and CEC. While several capillary-based separations exist for explosives, none address direct sampling from seawater, a sample matrix of particular interest in the detection of undersea mines. Direct comparisons are made between MEKC and CEC in terms of sensitivity and separation efficiency for the analysis of 14 explosives and explosive degradation products in seawater and diluted seawater. The use of high-salt stacking with MEKC results, on average, in a three-fold increase in the number of theoretical plates, and nearly double resolution for samples prepared in 25% seawater. By taking advantage of long injection times in conjunction with stacking, detection limits down to sub mg/L levels are attainable; however, resolution is sacrificed. CEC of explosive mixtures using sol-gels prepared from methyltrimethoxysilane does not perform as well as MEKC in terms of resolving power, but does permit extended injection times for concentrating analyte onto the head of the separation column with little or no subsequent loss in resolution. Electrokinetic injections of 8 min at high voltage allow for detection limits of explosives below 100 microg/L.     

Application of electron-attachment reactions to enhance selectivity of electron-capture detector for nitroaromatic explosives

The differences in the extent of electron-attachment reactions between thermal electrons and selected classes of organic molecules with high electron affinities were investigated. The investigations showed that interactions of thermal electrons with nitroaromatic compounds lead to the formation of neutral products with very low electron affinities. By contrast, a number of other analytes with high electron affinities such as polyhalogenated organic compounds, lead to products with high electron affinities. This difference was exploited to differentiate between nitroaromatic and polychlorinated organic compounds with a tandem arrangement consisting of two electron-capture detectors connected in series with an electron-attachment reactor.     

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.     

Inkjet printing lanthanide doped nanorods test paper for visual assays of nitroaromatic explosives

The facile and sensitive strategies for detections of nitroaromatic explosives are highly desirable in many challenging environments, especially for homeland security against terrorism. Here, we inkjet printed polyethylenimine (PEI)-coated Ce, Tb co-doped NaGdF₄ nanorods (NaGdF₄:Ce/Tb NRs) onto common filter paper to construct test paper for visual and instant detections of a typical explosive 2,4,6-trinitrophenol (TNP). Polyethylenimine molecules not only facilitate the formation of uniform NaGdF₄ nanorods but also provide specific recognized sites for TNP by the acid–base pairing interaction. The resultant TNP bound at the surface of PEI-coated NaGdF₄:Ce/Tb NRs can strongly quench the phosphorescence with a remarkably high quenching constant by the charge transfer mechanism from NaGdF₄:Ce/Tb NRs to TNP. By printing of the probe on a piece of filter paper, trace amounts of TNP can be visually detected by the appearance of a dark color against a bright green background under a UV lamp. This test paper can detect TNP as low as 0.45 ng mm⁻² by the naked eye, which provides a potential application in the rapid, on-line detections of explosives.     

Rearrangement energies for radicals of azido nitroaromatic compounds

Dissociation energies of C–N₃ bonds have been determined on the basis of data on the enthalpies of formation for a series of azido nitroaromatic compounds and the enthalpies of formation of radicals. Using fundamental relationships of chemical physics, a procedure has been suggested to calculate the energy of rearrangement of molecule fragments into radicals on the basis of special properties of rearrangement energy and the sums of average thermochemical energies for bonds comprising radical fragment in molecule. This calculation procedure provided a possibility to determine the energy of the N₃ moiety transformation into N₃ radical and the rearrangement energies of nitroaromatic radicals.     

Improvement of on-line solid-phase extraction for determining phenolic compounds in water

Summary Modifying the most common design for the on-line coupling of a precolumn to reversed phase LC with diode array detection has resulted in reduction of the broadening of the peaks which results when the compounds of interest are strongly retained by a highly hydrophobic sorbent. The modification consists of the desorption of the analytes trapped on the precolumn solely by the organic solvent used to modify the solvent strength of the mobile phase. Results obtained using this design were compared with those obtained with the conventional design, with C₁₈ and PLRP-S precolumns. The performance of the system was also tested with a highly cross-linked styrene-divinylbenzene copolymer (ENVI-chrom P) precolumn for the determination of phenolic compounds in real samples. The advantages and disadvantages are discussed. Ion-pair solid phase extraction is used in order to increase the breakthrough volumes of more polar compounds, mainly phenol. The use of the new design enables phenolic compounds to be determined at the low μg L⁻¹ level with limits of detection ranging between 0.1 and 2 μg L⁻¹ in tap water when a 10 mL sample was analyzed.     

Rational design of AIE-active biodegradable polycarbonates for high-performance WLED and selective detection of nitroaromatic explosives

Luminescent polymers have garnered considerable research attention for their excellent properties and wide range of applications in multi-responsive materials, bioimaging, and photoelectric devices. Thereout, various modulations of polymer structure are often the main approach to obtaining materials with different luminescent colors and functions. However, polymers with biodegradability, tunable color, and efficient emission simultaneously remain a challenge. Herein, we report a feasible strategy to achieve degradable and highly emissive polymers by exquisite combination and interplay of aggregation-induced emission (AIE) unit and environmental-friendly epoxide/CO₂ copolymerization. A series of polycarbonates P-TEP_xCN_y (x = 0, 1, 2, 4, 30, 120; y = 0, 1) were prepared, with emission color changed from blue to yellow by controlling the proportion of two designed AIE-active monomers. Among them, Using P-TCN as emitting layer, high performance white light-emitting diode (WLED) device with an external quantum efficiency (EQE) of 26.09% and CIE coordinates of (0.32, 0.32) was achieved. In addition, the designed polymers can be used as selective sensors for nitroaromatic compounds in their nanoaggregate states.     

Determination of trace levels of dinitrophenolic compounds by microporous membrane liquid-liquid extraction in environmental water samples

A fast and simple hollow fibre-based microporous membrane liquid-liquid extraction (MMLLE) method is proposed for the determination of trace levels of dinitrophenolic compounds in water samples. The optimization step was performed using a three-variables Doehlert matrix design, involving the fibre length, the quantity of trioctylphosphine oxide (TOPO) in the acceptor phase and the extraction time. Using the established experimental conditions, some other parameters such as stirring speed, salt content, humic acids and different organic solvents as the acceptor phase were studied. Validation of the method included calibration experiments, linearity studies and determination of method LOD (MLD). The RSD was around 11% in all the experiments on different days at different concentrations. Separation and detection of four dinitrophenols were performed in 10 min with an RP-LC and a C(8 )column ACN-citric buffer gradient elution and diode array detection.