Fragmentation study of hexanitrostilbene by ion trap multiple mass spectrometry and analysis by liquid chromatography/mass spectrometry

LC-MS/MS monitoring for explosives residues and OGSR with diverse ionization temperatures in soil & hands: 30 minutes for extraction + elution

A fast LC-APCI-MS/MS screening/confirmation method was developed and validated for trace analyses of 18 analytes which are explosives and organic gun shot residues including the challenging ones with diverse ionization conditions, in soil and on hands. (+) and (−) ionization modes were used after a single-step, low-volume solvent extraction procedure developed using methanol. Tape-lifting, stub, alcohol wipes, cotton bud were compared for collecting the residues from hands of a shooter. Tape-lifting and stub gave the highest recoveries and tape-lifting was chosen. Gradient elution system using ammonium chloride:methanol was developed. Whole procedure lasted approximately 30 min, was validated in both matrices, applied to real samples as post-blast residues, smokeless powder and the hands of a shooter, after shooting. Most of the recoveries were >80% and since all the precisions were <15%, quantitation was possible for all. Limit of Detection (LOD) and Limit of Quantification (LOQ) values were: 0.2–54.1 and 0.3–190.0 ngg−1 in soil, and 0.2–132.3 and 1.1–355.0 ngg−1 in tape-lift.

Optical and mass spectral characterization of the electrospray ionization/corona discharge ionization interface

The interchange between electrospray ionization (ESI) and corona discharge ionization (CDI) with respect to applied bias on the needle is customarily placed at the point where light production begins at the tip of the needle. If a liquid sample is flowing through a needle that is observed to produce light, the ionization process is assumed to be harsher and the term coronaspray ionization has been coined to describe this hybrid ionization mechanism. In this work, the transition between ESI and CDI is investigated with respect to applied bias through optical and mass spectrometric measurements. As a function of applied bias potential, the optical signal at the tip of the needle was recorded simultaneously with the resultant ionization products. In this effort, the production of ions from an electrospray ionization needle has been demonstrated to produce light regardless of bias if ions are also formed. With this understanding, an ESI/CDI needle was designed to allow the bias to be temporarily pulsed over the 'onset' voltage necessary for ionization and the rise and decay of the optical signal was measured. Positive mode CDI onset to a stable discharge state within 0.05 ms, while positive ESI required 1.9 ms to reach a stable condition. In the negative mode, the stability of the ionization process was highly variable in both ESI and CDI modes, though CDI was generally faster to reach the stable mode of operation. When the resultant ions were investigated, the effect of increased bias on an ESI needle was found to be species-dependent. Recognizing that the range of compounds probed was limited, for those examined, it appears that stable, non-labile species may be investigated via ESI under extremely high biases while labile species demonstrate a narrow range of stable biases before significant fragmentation occurs.

Identification and analysis of organic explosives from post-blast debris by nuclear magnetic resonance

The growing threat of terrorism has triggered an urgent need to find effective ways to improve the analysis of explosives. This will aid forensic scientists in analysing the post-blast debris, which in turn helps the law enforcement agencies to frame suitable regulations. Analysis of post-blast debris is challenging as it hosts a massive amount of complexity. There are various techniques reported till date such as mass spectrometry, gas chromatography, high-performance liquid chromatography, Fourier transform infrared spectroscopy, and Raman spectroscopy for the analysis of post-blast residues. However, none of them has been able to identify the structural composition of the explosives. The current research study focuses on identifying the structural composition of the explosives from the post-blast debris using the nuclear magnetic resonance (NMR) technology. The post-blast analytes were extracted from soil samples, cleaned by the solid phase extraction (SPE) method and were rapidly analysed by the nuclear magnetic resonance spectrometer. This paper reports the identification of nitro organic explosives such as pentaerythritol tetranitrate (PETN), trinitrotoluene (TNT) and 2,4,6-trinitrophenylmethylnitramine (tetryl) in post-blast debris by 400 MHz nuclear magnetic resonance spectrometer.

Multifunctional Flexible SERS Sensor on a Fixate Gel Pad: Capturing, Derivation, and Selective Picogram Indirect Detection of Explosive 2,2',4,4',6,6'-Hexanitrostilbene

2,2',4,4',6,6'-Hexanitrostilbene (HNS) is an explosive with better explosion performance than the well-known 2,4,6-trinitrotoluene (TNT). Surprisingly, unlike other nitroaromatic explosives, there are limited reports regarding the detection of the HNS, let alone sensing reports on surface residues. In this work, a multifunctional flexible SERS sensor was proposed for the indirect detection of HNS based on the transparent fixate gel pads. The sticky and flexible gel pad can effectively collect any HNS surface residues. The inherent amine groups within the gel pad of which the main ingredient is polyurethane can react with HNS to form the orange Meisenheimer-alike complex. The modification of Ag NPs with halide ions was screened for the best SERS performance. KI-modified-citrate-reduced Ag NPs showed selective but enormous SERS enhancement for the HNS derivative. The detection of HNS in the solution phase was explored, and a linear range of 0.01-25 ppm was achieved. The lowest detectable amount (LDA) of HNS was found to be 50 pg, making it one of the most sensitive methods in literature. It was successfully utilized for the HNS residues sensing on fingerprints and bags with LDAs of 5 and 200 ng, respectively. In addition, other explosives including TATB, LLM-105, RDX, HMX, FOX-7, and TNT were also examined to assess the selectivity of the fixate. It was found that the fixate showed excellent selectivity for HNS.

Exploration of an odorous aldehydes and ketones produced by Uroglena americana using high resolution mass spectrometry, GC-Olfactometry, and multivariate analysis

Off-flavor events in tap water have been reported from various regions of Japan. Fishy smell is the second most common off-flavor in Japan and Uroglena americana (U. americana) is known to be a major contributor to the smell. However, the causative compound of the smell it produces still remains unrevealed to the best of our knowledge. In this study, an exploration of odorous aldehydes and ketones originating from U. americana was performed with a view to discovering a possible candidate substance of causative compounds. Environmental samples containing U. americana colony and cultured media with U. americana were analyzed with two high resolution mass spectrometers, one of them is coupled with liquid chromatography (LC-HRMS), and the other is with gas chromatography and a sniffing port (GC-O-HRMS). Multivariate analyses (MVA) were utilized to explore a compound that is likely to be odorous aldehydes or ketones with a reduced time of exploration. A combination of LC-HRMS and MVA resulted in the selection of one candidate substance and its formula was determined to be C₁₃H₂₀O₃ on the basis of its accurate mass and natural isotopic pattern. The candidate substance underwent GC-O-HRMS analyses and milk-like smell was detected at around its retention time. Although the detected smell was different from fishy smell, it is expected that the fishy smell is caused by multiple compounds to which the candidate substance belongs. First generation product ion spectra of the candidate substance suggested that it contains a hydroxyl group, a cyclohexene ring, and a ketone moiety.

Differentiation of isomeric dinitrotoluenes and aminodinitrotoluenes using electrospray high resolution mass spectrometry

Explosive detection and identification play an important role in the environmental and forensic sciences. However, accurate identification of isomeric compounds remains a challenging task for current analytical methods. The combination of electrospray multistage mass spectrometry (ESI-MS(n) ) and high resolution mass spectrometry (HRMS) is a powerful tool for the structure characterization of isomeric compounds. We show herein that resonant ion activation performed in a linear quadrupole ion trap allows the differentiation of dinitrotoluene isomers as well as aminodinitrotoluene isomers. The explosive-related compounds: 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), 2-amino-4,6-dinitrotoluene (2A-4,6-DNT) and 4-amino-2,6-dinitrotoluene (4A-2,6-DNT) were analyzed by ESI-MS in the negative ion mode; they produced mainly deprotonated molecules [M - H](-) . Subsequent low resolution MS(n) experiments provided support for fragment ion assignments and determination of consecutive dissociation pathways. Resonant activation of deprotonated dinitrotoluene isomers gave different fragment ions according to the position of the nitro and amino groups on the toluene backbone. Fragment ion identification was bolstered by accurate mass measurements performed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS). Notably, unexpected results were found from accurate mass measurements performed at high resolution for 2,6-DNT where a 30-Da loss was observed that corresponds to CH2 O departure instead of the expected isobaric NO(•) loss. Moreover, 2,4-DNT showed a diagnostic fragment ion at m/z 116, allowing the unambiguous distinction between 2,4- and 2,6-DNT isomers. Here, CH2 O loss is hindered by the presence of an amino group in both 2A-4,6-DNT and 4A-2,6-DNT isomers, but nevertheless, these isomers showed significant differences in their fragmentation sequences, thus allowing their differentiation. DFT calculations were also performed to support experimental observations.

A fast liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) method for the identification of organic explosives and propellants

A fast, highly specific and sensitive method for the detection of an extensive list of organic explosives and propellants using an optimised Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry (LC-QToF-MS) procedure has been developed. Analyte specific information including retention time, adduct accurate mass and fragmentation data was firstly collected using both positive and negative ion Atmospheric Pressure Chemical Ionisation (APCI) and entered into a Personal Compound Database/Library (PCDL). The custom PCDL can then be used to screen any sample for the presence of organic explosives and propellants, generating a match score for any identified compounds. To date over 50 organic explosives and propellants have been characterised and entered into the database representing those likely to be encountered in forensic and environmental samples and also a range of specialist explosives.

Ion spectrometric detection technologies for ultra-traces of explosives: a review

In recent years, explosive materials have been widely employed for various military applications and civilian conflicts; their use for hostile purposes has increased considerably. The detection of different kind of explosive agents has become crucially important for protection of human lives, infrastructures, and properties. Moreover, both the environmental aspects such as the risk of soil and water contamination and health risks related to the release of explosive particles need to be taken into account. For these reasons, there is a growing need to develop analyzing methods which are faster and more sensitive for detecting explosives. The detection techniques of the explosive materials should ideally serve fast real-time analysis in high accuracy and resolution from a minimal quantity of explosive without involving complicated sample preparation. The performance of the in-field analysis of extremely hazardous material has to be user-friendly and safe for operators. The two closely related ion spectrometric methods used in explosive analyses include mass spectrometry (MS) and ion mobility spectrometry (IMS). The four requirements-speed, selectivity, sensitivity, and sampling-are fulfilled with both of these methods.

Negative ion-atmospheric pressure photoionization: electron capture, dissociative electron capture, proton transfer, and anion attachment

To better guide the development of liquid chromatography/electron capture-atmospheric pressure photoionization-mass spectrometry (LC/EC-APPI-MS) in analysis of low polarity compounds, the ionization mechanism of 19 compounds was studied using dopant assisted negative ion-APPI. Four ionization mechanisms, i.e., EC, dissociative EC, proton transfer, and anion attachment, were identified as being responsible for the ionization of the studied compounds. The mechanisms were found to sometimes compete with each other, resulting in multiple ionization products from the same molecule. However, dissociative EC and proton transfer could also combine to generate the same [M - H](-) ions. Experimental evidence suggests that O(2)(-*), which was directly observed in the APPI source, plays a key role in the formation of [M - H](-) ions by way of proton transfer. Introduction of anions more basic than O(2)(-*), i.e., C(6)H(5)CH(2)(-), into the APPI source, via addition of di-tert-butyl peroxide in the solvent and/or dopant, i.e., toluene, enhanced the deprotonation ability of negative ion-APPI. Although the use of halogenated solvents could hinder efficient EC, dissociative EC, and proton transfer of negative ion-APPI due to their EC ability, the subsequently generated halide anions promoted halide attachment to compounds that otherwise could not be efficiently ionized. With the four available ionization mechanisms, it becomes obvious that negative ion-APPI is capable of ionizing a wider range of compounds than negative ion chemical ionization (NICI), negative ion-atmospheric pressure chemical ionization (negative ion-APCI) or negative ion-electrospray ionization (negative ion-ESI).

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.