Gas chromatography, liquid chromatography and ion chromatography adapted to the trace analysis of explosives

Investigations into the source attribution of party sparklers using trace elemental analysis and chemometrics

In Australia, party sparklers are commonly used to initiate or prepare inorganic based homemade explosives (HMEs) as they are the most easily accessible and inexpensive pyrotechnic available on the market. As sparkler residue would be encountered in cases involving these types of devices, the characterisation and source determination of the residue would be beneficial within a forensic investigation. The aim of this study is to demonstrate the potential of using trace elemental profiling coupled with chemometric and other statistical techniques to link a variety of different sparklers to their origin. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to determine the concentration of 50 elements in 48 pre-blast sparkler samples from eight sparkler brands/classes available in Australia. Extracting ground-up sparkler residue in 10% nitric acid for 24 hours was found to give the most reliable quantification. The collected data were analysed using Principal Component Analysis (PCA) to visualise the distribution of the sample data and explore whether the sparkler samples could be classified into their respective brands. ANOVA based feature selection was used to remove elements that did not largely contribute to the separation between classes. This resulted in the development of a 7-elemental profile, consisting of V, Co, Ni, Sr, Sn, Sb, W, which could be used to correctly classify the samples into eight distinct groups. Linear Discriminant Analysis (LDA) was subsequently used to construct a discriminant model using four out of six samples from each class. The model successfully classified 100% of the samples to their correct sparkler brand. The model also correctly matched 100% of the remaining samples to the correct class. This demonstrates the potential of using trace elemental analysis and chemometrics to correctly identify and discriminate between party sparklers.

Chemical Classification of Explosives

This work comprehensively reviews some fundamental concepts about explosives and their two commonly used classifications based on either their velocity of detonation or their application. These classifications are highly useful in the military/legal field, but completely useless for the chemical determination of explosives. Because of this reason, a classification of explosives based on their chemical composition is comprehensively revised, discussed and updated. This classification seeks to merge those dispersed chemical classifications of explosives found in literature into a unique general classification, which might be useful for every researcher dealing with the analytical chemical identification of explosives. In the knowledge of the chemical composition of explosives, the most adequate analytical techniques to determine them are finally discussed.

Pt(II)C∧N∧N-Based Luminophore-Micelle Adducts for Sensing Nitroaromatic Explosives

Two luminescent cyclometalated Pt(II)-complexes, 1•Pt and 2•Pt, respectively, were synthesized by using unsymmetrical C^∧N^∧N ligands having different alkyl substituents. These π-electron-rich complexes are used for sensing various electron deficient nitroaromatic explosives, e.g., 4-nitrotoluene (NT), 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT), and 2,4,6-trinitrophenol (TNP), in aqueous, nonaqueous, as well as in the solid state as a paper strip with maximum detection limit of ca. 10^-9 M. It was demonstrated that the sparingly soluble 2•Pt complex becomes water-soluble in the presence of all kinds of surfactants, viz., cationic (e.g., cetyltrimethylammonium bromide, CTAB), anionic (e.g., sodium dodecyl sulfate, SDS), and neutral (e.g., Triton X-100). This may be due to the incorporation of its long lyophilic tail group (-C₁₂H₂₅) inside the micellar core, exposing planar Pt(II)C^∧N^∧N headgroup to the aqueous bulk phase. It was also observed that the extent of solubility of these Pt(II)-complexes in micellar media strongly depends on the length of the existing alkyl chain. For instance, the presence of longer dodecyl chain makes 2•Pt complex ca. 1000-fold more soluble than the complex 1•Pt, which contains a shorter propyl chain. Their sensing behavior essentially arises by the quenching of Pt(II)-based intense luminescence due to the supramolecular charge transfer (CT) process originating from Pt(II)C^∧N^∧N-antenna to the electron deficient nitroaromatic explosives. Our present work shows that the micellar adducts formed by highly luminophoric material and surfactant molecules could effectively detect such explosives in aqueous medium with better sensitivity compared to what were observed in other media.

Effective collection and detection of airborne species using SERS-based detection and localized electrodynamic precipitation

Three different delivery concepts (standard diffusion, global electrodynamic precipitation, and localized nanolens-based precipitation) and three different SERS enhancement layers (a silver film, a nanolens-based localized silver nanoparticle film, and the standard AgFON) are compared. The nanolens concept is applied to increase the SERS signal: a factor of 633, when compared to a standard mechanism of diffusion, is observed.

Effective localized collection and identification of airborne species through electrodynamic precipitation and SERS-based detection

Various nanostructured sensor designs currently aim to achieve or claim single molecular detection by a reduction of the active sensor size. However, a reduction of the sensor size has the negative effect of reducing the capture probability considering the diffusion-based analyte transport commonly used. Here we introduce and apply a localized programmable electrodynamic precipitation concept as an alternative to diffusion. The process provides higher collection rates of airborne species and detection at lower concentration. As an example, we compare an identical nanostructured surfaced-enhanced Raman spectroscopy sensor with and without localized delivery and find that the sensitivity and detection time is improved by at least two orders of magnitudes. Localized collection in an active-matrix array-like fashion is also tested, yielding hybrid molecular arrays on a single chip over a broad range of molecular weights, including small benzenethiol (110.18 Da) and 4-fluorobenzenethiol (128.17 Da), or large macromolecules such as anti-mouse IgG (~150 kDa).

Determination of nitroaromatic and nitramine explosives from a PTFE wipe using thermal desorption-gas chromatography with electron-capture detection

A method for the detection of nitroaromatic and nitramine explosives from a PTFE wipe has been developed using thermal desorption andgas chromatography with electron-capture detection (TD-GC-ECD). For method development a standard mixture containing eight nitroaromatic and two nitramine (HMX and RDX) explosive compounds was spiked onto a PTFE wipe. Explosives were desorbed from the wipe in a commercial thermal desorption system and trapped onto a cooled injection system, which was incorporated into the injection port of the GC. A dual column, dual ECD configuration was adopted to enable simultaneous confirmation analysis of the explosives desorbed. For the desorption of 50 ng of each explosive, desorption efficiencies ranged between 80.0 and 117%, for both columns. Linearity over the range 2.5-50 ng was demonstrated for each explosive on both columns with r2 values ranging from 0.979 to 0.991 and limits of detection less than 4 ng. Desorption of HMX from a PTFE wipe has also been demonstrated for the first time, albeit at relatively high loadings (100 ng).

Explosives detection: a challenge for physical chemistry

The detection of explosives, energetic materials, and their associated compounds for security screening, demining, detection of unexploded ordnance, and pollution monitoring is an active area of research. A wide variety of detection methods and an even wider range of physical chemistry issues are involved in this very challenging area. This review focuses on techniques such as optical and mass spectrometry and chromatography for detection of trace amounts of explosives with short response times. We also review techniques for detecting the decomposition fragments of these materials. Molecular data for explosive compounds are reviewed where available.

Explosives detection in soil using a field-portable continuous flow immunosensor

A field method for quantitative analysis of explosives in contaminated soil samples is described. The method is based on a displacement immunoassay performed in a commercial instrument, the FAST 2000, engineered by Research International Inc. The method can be used on-site to measure 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) within 5min. For this study, replicate analyses were performed on soil extracts prepared from each field sample as well as appropriate controls, blanks, and laboratory standards. Statistical analyses were done to assess accuracy, bias, and predictability of the method. The results demonstrated that the immunosensor could be used effectively to screen environmental samples for the presence or absence of explosives. In most samples, the method also provided quantitative values that were in good agreement with standard laboratory analyses using HPLC. A limited number of sample matrices interfered with the immunoassay and produced results that varied significantly from the laboratory data. In each case, the compounds causing the problem have been identified and efforts are being made to minimize these matrix interferences in future field evaluations.

High-speed fluorescence detection of explosives-like vapors

In this paper, we report on the preparation of novel cross-reactive optical microsensors for high-speed detection of low-level explosives and explosives-like vapors. Porous silica microspheres with an incorporated environmentally sensitive fluorescent dye are employed in high-density sensor arrays to monitor fluorescence changes during nitroaromatic compound (NAC) vapor exposure. The porous silica-based sensor materials have good adsorption characteristics, high surface areas, and surface functionality to help maximize analyte-dye interactions. These interactions occur immediately upon vapor exposure, i.e., in less than 200 ms and are monitored with a high-speed charge-coupled device camera to produce characteristic and reproducible vapor response profiles for individual sensors within an array. Employing thousands of identical microsensors permits sensor responses to be combined, which significantly reduces sensor noise and enhances detection limits. Normalized response profiles for 1,3-dinitrobenzene (1,3-DNB) are independent of analyte concentration, analyte exposure time, or sensor age for an array of one sensor type. Explosives-like NACs such as 2,4-dinitrotoluene and DNB are detected at low part-per-billion levels in seconds. Sensor-analyte profiles of some sensor types are more sensitive to low-level NAC vapor even when in a higher organic vapor background. We show that single-element arrays permit the detection of low-level nitroaromatic compound vapors because of sensor-to-sensor reproducibility and signal averaging.