Fast detection of triacetone triperoxide (TATP) from headspace using planar solid-phase microextraction (PSPME) coupled to an IMS detector

Recent development and trends in the detection of peroxide-based explosives

Peroxide-based explosives (PBEs) are increasingly common in criminal and terrorist activity due to their easy synthesis and high explosive power. The rise in terrorist attacks involving PBEs has heightened the importance of detecting trace amounts of explosive residue or vapors. This paper aims to provide a review on the developments of techniques and instruments for detecting PBEs over the past ten years, specifically discussing advancements in ion mobility spectrometry, ambient mass spectrometry, fluorescence techniques, colorimetric methods, and electrochemical methods. We provide examples to illustrate their evolution and focus on new strategies for improving detection performance, specifically in terms of sensitivity, selectivity, high-throughput, and wide explosives coverage. Finally, we discuss future prospects for PBE detection. It is hoped this treatment will serve as a guide to the novitiate and as aid memoire to the researchers.

Determination of triacetone triperoxide (TATP) traces using passive samplers in combination with GC-MS and GC-PCI-MS/MS methods

The use of organic peroxides for the preparation of homemade explosives (HMEs) is common among terrorists due to inexpensive precursor chemicals and simple synthetic procedures. Triacetone triperoxide (TATP) is the most notable peroxide explosive, and has been deployed in several terrorist attacks as explosive filling of improvised explosive devices (IEDs). Forensic identification of TATP in pre-blast and post-blast residues, including on-site analysis, poses significant analytical challenges and induces demand for practicable and sensitive detection techniques. This work presents a concept suitable for laboratory and on-site identification of TATP residues in liquid samples (aqueous TATP synthetic waste) and in gas phase. It is based on TATP enrichment from the aqueous or gas phase using different types of passive samplers (polydimethylsiloxane (PDMS) sampling rods and activated carbon sampling tubes (ACST)) and subsequent identification of the explosive by gas chromatography-mass spectrometry (GC-MS) or GC with positive chemical ionization and tandem MS (GC-PCI-MS/MS) analytical techniques. Additionally, investigation of the stability of TATP in aqueous solutions and of the stability of enriched TATP in passive samplers under different storage conditions, as well as development of TATP re-extraction procedures from passive samplers have been performed in this study. The practical use of passive samplers was demonstrated during and after TATP production processes. Moreover, post-blast sampling of TATP under different conditions of controlled blasting events was investigated using the passive sampling concept.

Triacetone triperoxide characterization by FT-ICR mass spectrometry: Uncovering multiple forensic evidence

Triacetone triperoxide is one of the most common used explosives by terrorist and criminal groups, being easily synthesized with over the counter reagents. Moreover, it's difficult to detect since it contains no nitrogen. Extreme resolution mass spectrometry, based on Fourier transform ion cyclotron resonance mass spectrometry provides a way to established its composition, being able to detect its presence in complex matrixes. In this work, we investigated the detailed chemical composition of triacetone triperoxide and analysed latent fingerprints for evidence of its handling. Our results allowed the characterization of the oligoperoxides formed in the synthesis of triacetone triperoxide: oligomers dihydroperoxy terminated [H(OOC(CH₃)₂)_nOOH] and the oligomeric acetone carbonyl oxides terminated as hydroperoxides [H(O₂C(CH₃)₂)_nOOC(O)CH₃]. The discrimination between the different synthetic routes using different acid catalysts is possible given the clear differences between the mass spectrum corresponding to each case. Moreover, we identified triacetone triperoxide in latent fingerprints following its manipulation. For criminal investigation, in addition to the unambiguous detection and identification of the explosive, it is of the highest interest to identify the reagents used, who produced it and who used it for criminal purposes.

Detection of Triacetone Triperoxide (TATP) Precursors with an Array of Sensors Based on MoS₂/RGO Composites

Triacetone triperoxide (TATP) is a self-made explosive synthesized from the commonly used chemical acetone (C₃H₆O) and hydrogen peroxide (H₂O₂). As C₃H₆O and H₂O₂ are the precursors of TATP, their detection is very important due to the high risk of the presence of TATP. In order to detect the precursors of TATP effectively, hierarchical molybdenum disulfide/reduced graphene oxide (MoS₂/RGO) composites were synthesized by a hydrothermal method, using two-dimensional reduced graphene oxide (RGO) as template. The effects of the ratio of RGO to raw materials for the synthesis of MoS₂ on the morphology, structure, and gas sensing properties of the MoS₂/RGO composites were studied. It was found that after optimization, the response to 50 ppm of H₂O₂ vapor was increased from 29.0% to 373.1%, achieving an increase of about 12 times. Meanwhile, all three sensors based on MoS₂/RGO composites exhibited excellent anti-interference performance to ozone with strong oxidation. Furthermore, three sensors based on MoS₂/RGO composites were fabricated into a simple sensor array, realizing discriminative detection of three target analytes in 14.5 s at room temperature. This work shows that the synergistic effect between two-dimensional RGO and MoS₂ provides new possibilities for the development of high performance sensors.

Ammonia-Assisted Proton Transfer Reaction Mass Spectrometry for Detecting Triacetone Triperoxide (TATP) Explosive

Proton transfer reaction mass spectrometry (PTR-MS) usually detects different types of compounds by changing the discharge gas to produce different reagent ions in the ion source. In the present work, a novel method of changing reagent ions, ammonia-assisted PTR-MS, was developed. Through an injection port bypass, ammonia was injected into a homemade PTR-MS device. A conventional PTR-MS apparatus with reagent ions H₃O⁺(H₂O)_n (n = 0, 1, 2) can be converted to an ammonia-assisted PTR-MS with reagent ions NH₄⁺.The new method was introduced to detect triacetone triperoxide (TATP) explosive material. Results showed that the sensitivity is enhanced more than 37 times compared with TATP detection using conventional PTR-MS and the limit of detection (LOD) could reach 1.3 ppb. TATP in real complex matrixes can also be detected successfully using this method. Compared to conventional PTR-MS, ammonia-assisted PTR-MS has better sensitivity and better LOD for TATP detection, and the technique provides common users with a convenient and quick method to change reagent ions. The users of PTR-MS can easily obtain other reagent ions by injecting different assisted gases into an injection port to meet different detection needs. Graphical Abstract.

Trace analysis by ion mobility spectrometry: From conventional to smart sample preconcentration methods. A review

Ion mobility spectrometry (IMS) is a rapid and high sensitive technique widely used in security and forensic areas. However, a lack of selectivity is usually observed in the analysis of complex samples due to the scarce resolution of the technique. The literature concerning the use of conventional and novel smart materials in the pretreatment and preconcentration of samples previous to IMS determinations has been critically reviewed. The most relevant strategies to enhance selectivity and sensitivity of IMS determinations have been widely discussed, based in the use of smart materials, as immunosorbents, aptamers, molecularly imprinted polymers (MIPs), ionic liquids (ILs) and nanomaterial. The observed trend is focused on the development of IMS analytical methods in combination of selective sample treatments in order to achieve quick, reliable, sensitive, and selective methods for the analysis of complex samples such as biological fluids, food, or environmental samples.

Sorbent Film-Coated Passive Samplers for Explosives Vapour Detection Part A: Materials Optimisation and Integration with Analytical Technologies

A new thin-film passive sampler is presented as a low resource dependent and discrete continuous monitoring solution for explosives-related vapours. Using 15 mid-high vapour pressure explosives-related compounds as probes, combinations of four thermally stable substrates and six film-based sorbents were evaluated. Meta-aramid and phenylene oxide-based materials showed the best recoveries from small voids (~70%). Analysis was performed using liquid chromatography-high resolution accurate mass spectrometry which also enabled tentative identification of new targets from the acquired data. Preliminary uptake kinetics experiments revealed plateau concentrations on the device were reached between 3–5 days. Compounds used in improvised explosive devices, such as triacetone triperoxide, were detected within 1 hour and were stably retained by the sampler for up to 7 days. Sampler performance was consistent for 22 months after manufacture. Lastly, its direct integration with currently in-service explosives screening equipment including ion mobility spectrometry and thermal desorption mass spectrometry is presented. Following exposure to several open environments and targeted interferences, sampler performance was subsequently assessed and potential interferences identified. High-security building and area monitoring for concealed explosives using such cost-effective and discrete passive samplers can add extra assurance to search routines while minimising any additional burden on personnel or everyday site operation.

The gas chromatographic analysis of the reaction products of the partial isobutane oxidation as a two phase process

The partial oxidation of isobutane to t-butyl hydroperoxide (TBHP) has been studied analytically for the first time as a two-phase process in a capillary micro reactor. In order to obtain detailed information on products, yields, selectivities and reaction pathways, the products have been investigated by GC/MS. An Rxi-5ms column and a PTV-injector have been used to analyze the liquid products. TBHP, di-t-butyl peroxide (DTBP), t-butanol (TBA), and propanone as main products as well as further by-products e.g. methanal, isopropanol, isobutanol and isobutanal in minor quantities have been identified by MS. The liquid products have been obtained by quenching the reaction and vaporizing the isobutane afterwards by pressure reduction using a mass flow controller allowing a constant mass flow. For all liquid reaction products calibrations, a validation of the method including limits of quantification and detection as well as calculation of uncertainties has been performed. The results have been applied successfully for the investigation of the selectivities of the main products (TBHP, DTBP, TBA, propanone) of the isobutane oxidation. In the frame of the analytical investigation of this reaction a correlation coefficient of r(2)>0.999 for TBHP and DTBP, which is necessary to perform a validation, has been obtained for the first time. The gaseous phase has been analyzed using a GASPRO column, a DEANS switch, a mole sieve column and a TCD detector. Apart from the gaseous reactants, isobutene has been found.

Advances in explosives analysis--part I: animal, chemical, ion, and mechanical methods

The number and capability of explosives detection and analysis methods have increased substantially since the publication of the Analytical and Bioanalytical Chemistry special issue devoted to Explosives Analysis (Moore and Goodpaster, Anal Bioanal Chem 395(2):245-246, 2009). Here we review and critically evaluate the latest (the past five years) important advances in explosives detection, with details of the improvements over previous methods, and suggest possible avenues towards further advances in, e.g., stand-off distance, detection limit, selectivity, and penetration through camouflage or packaging. The review consists of two parts. This part, Part I, reviews methods based on animals, chemicals (including colorimetry, molecularly imprinted polymers, electrochemistry, and immunochemistry), ions (both ion-mobility spectrometry and mass spectrometry), and mechanical devices. Part II will review methods based on photons, from very energetic photons including X-rays and gamma rays down to the terahertz range, and neutrons.

Differentiation among peroxide explosives with an optoelectronic nose

Forensic identification of batches of homemade explosives (HME) poses a difficult analytical challenge. Differentiation among peroxide explosives is reported herein using a colorimetric sensor array and handheld scanner with a field-appropriate sampling protocol. Clear discrimination was demonstrated among twelve peroxide samples prepared from different reagents, with a classification accuracy >98%.

Detection of tetrahydrocannabinol residues on hands by ion-mobility spectrometry (IMS). Correlation of IMS data with saliva analysis

Ion-mobility spectroscopy (IMS) was evaluated as a high-throughput, cheap, and efficient analytical tool for detecting residues of tetrahydrocannabinol (THC) on hands. Regarding the usefulness of hand residues as potential samples for determining THC handling and abuse, we studied the correlation between data obtained from cannabis consumers who were classified as positive after saliva analysis and from those who were classified as positive on the basis of the information from hand-residue analysis. Sampling consisted of wiping the hands with borosilicate glass microfiber filters and introducing these directly into the IMS after thermal desorption. The possibility of false positive responses, resulting from the presence of other compounds with a similar drift time to THC, was evaluated and minimised by applying the truncated negative second-derivative algorithm. The possibility of false negative responses, mainly caused by competitive ionisation resulting from nicotine, was also studied. Graphical abstract THC residues: from hands to analytical signals.

Review on ion mobility spectrometry. Part 1: current instrumentation

Ion Mobility Spectrometry (IMS) is a widely used and 'well-known' technique of ion separation in the gaseous phase based on the differences in ion mobilities under an electric field. All IMS instruments operate with an electric field that provides space separation, but some IMS instruments also operate with a drift gas flow that provides also a temporal separation. In this review we will summarize the current IMS instrumentation. IMS techniques have received an increased interest as new instrumentation and have become available to be coupled with mass spectrometry (MS). For each of the eight types of IMS instruments reviewed it is mentioned whether they can be hyphenated with MS and whether they are commercially available. Finally, out of the described devices, the six most-consolidated ones are compared. The current review article is followed by a companion review article which details the IMS hyphenated techniques (mainly gas chromatography and mass spectrometry) and the factors that make the data from an IMS device change as a function of device parameters and sampling conditions. These reviews will provide the reader with an insightful view of the main characteristics and aspects of the IMS technique.

Cavitand-based solid-phase microextraction coating for the selective detection of nitroaromatic explosives in air and soil

A selective cavitand-based solid-phase microextraction coating was synthesized for the determination of nitroaromatic explosives and explosive taggants at trace levels in air and soil. A quinoxaline cavitand functionalized with a carboxylic group at the upper rim was used to enhance selectivity toward analytes containing nitro groups. The fibers were characterized in terms of film thickness, morphology, thermal stability, and pH resistance. An average coating thickness of 50 (±4) μm, a thermal stability until 400 °C, and an excellent fiber-to-fiber and batch to batch repeatability with RSD lower than 4% were obtained. The capabilities of the developed coating for the selective sampling of nitroaromatic explosives were proved achieving LOD values in the low ppbv and ng kg(-1) range, respectively, for air and soil samples.

Sensitivity of TATP to a TASER electrical output

A series of experiments were performed to evaluate and document the effect of a TASER ("stun gun") on triacetone triperoxide (TATP), an easily manufactured explosive used often in IEDs and suicide bombing vests. TATP samples were synthesized and subjected to several tests of their sensitivity. These samples were run through a BAM Friction test with a result of <0.5 N, Impact Test with a result of 5.8 ± 0.4 cm, and Electrostatic Discharge test with a result of 0.073 ± 0.018 J. In addition, TATP was shocked with a TASER in a variety of configurations. The TATP reacted in 17/17 tests when the TASER arced through the TATP and 0/4 times when the TATP was configured in such a way that the TATP was not subjected to the electrical arc. Based on the experimental data, TATP will readily explode in a variety of configurations by a TASER or similar device. Testing should be expanded, as the data presented here are limited to a single formulation of TATP. Just one of a large array of TASER-like devices by a single manufacturer were tested; other devices, scenarios and formulations of TATP and other likely threat materials should be assessed.

Application of Receiver Operating Characteristic (ROC) Curves for Explosives Detection Using Different Sampling and Detection Techniques

Reported for the first time are receiver operating characteristic (ROC) curves constructed to describe the performance of a sorbent-coated disk, planar solid phase microextraction (PSPME) unit for non-contact sampling of a variety of volatiles. The PSPME is coupled to ion mobility spectrometers (IMSs) for the detection of volatile chemical markers associated with the presence of smokeless powders, model systems of explosives containing diphenylamine (DPA), 2,4-dinitrotoluene (2,4-DNT) and nitroglycerin (NG) as the target analytes. The performance of the PSPME-IMS was compared with the widely accepted solid-phase microextraction (SPME), coupled to a GC-MS. A set of optimized sampling conditions for different volume containers (1–45 L) with various sample amounts of explosives, were studied in replicates (n = 30) to determine the true positive rates (TPR) and false positive detection rates (FPR) for the different scenarios. These studies were obtained in order to construct the ROC curves for two IMS instruments (a bench-top and field-portable system) and a bench top GC-MS system in low and high clutter environments. Both static and dynamic PSPME sampling were studied in which 10–500 mg quantities of smokeless powders were detected within 10 min of static sampling and 1 min of dynamic sampling.