Evaluation of false positive responses by mass spectrometry and ion mobility spectrometry for the detection of trace explosives in complex samples

Practical Applications of Secondary/Extractive Electrospray Ionization (SESI): A Versatile Tool for Real-Time Chemical Analysis

In the 1980s, researchers discovered the remarkable ability of electrospray plumes to effectively ionize gas-phase molecules via secondary ionization. Around 20 years later-coinciding with the ambient mass spectrometry revolution-secondary electrospray ionization (SESI) and extractive electrospray ionization (EESI) coupled to mass spectrometry were revisited and further developed to analyze complex mixtures of gas and aerosol samples in real-time yet with high sensitivity. During the past two decades, these mass spectrometric techniques have been applied across a broad range of applications, such as the detection of illicit drugs, environmental aerosol analysis, and a series of metabolomic studies through the analysis of volatiles emitted from living organisms. This review offers a comprehensive overview of the progress of SESI and EESI applications since their emergence. Finally, we discuss the opportunities, challenges, along with future directions of SESI and EESI techniques.

Pursuing drug laboratories: Analysis of drug precursors with High Kinetic Energy Ion Mobility Spectrometry

High Kinetic Energy Ion Mobility Spectrometry (HiKE-IMS) is a technique for rapid and reliable detection of trace compounds down to ppbV-levels within one second. Compared to classical IMS operating at ambient pressure and providing the ion mobility at low electric fields, HiKE-IMS can also provide the analyte-specific field dependence of the ion mobility and a fragmentation pattern at high reduced electric field strengths. The additional information about the analyte obtained by varying the reduced electric field strength can contribute to reliable detection. Furthermore, the reduced number of ion-molecule reactions at the low operating pressure of 10 - 40 mbar and the shorter reaction times reduce the impact of competing ion-molecule reactions that can cause false negatives. In this work, we employ HiKE-IMS for the analysis of phenyl-2-propanone (P2P) and other precursor chemicals used for synthesis of methamphetamine and amphetamine. The results show that the precursor chemicals exhibit different behavior in HiKE-IMS. Some precursors form a single significant ion species, while others readily form a fragmentation pattern. Nevertheless, all drug precursors can be distinguished from each other, from the reactant ions and from interfering compounds. In particular, the field-dependent ion mobility as an additional separation dimension aids identification, potentially reducing the number of false positive alarms in field applications. Furthermore, the analysis of a seized illicit P2P sample shows that even low levels of P2P can be detected despite the complex background present in the headspace of real samples.

Ultrafast Gas Chromatography-Tandem Differential Mobility Spectrometry: Toward A New Generation of On-Site, Real-Time Trace-Explosives Detection

In the defense and security sector, rapid detection of trace quantities of threat materials is paramount. Traditional instrumentation typically relies on standalone ion mobility techniques due to being inexpensive, portable, and highly sensitive. However, these techniques face limitations when handling complex samples, suffering from low resolving power (often less than 100) and ion-suppression effects, which can lead to false-positive and false-negative results. Here, we present a foundation to the solution through the hyphenation of the flow field thermal gradient gas chromatograph (FF-TG-GC) developed by HyperChrom with a tandem differential ion mobility spectrometer (DMS-DMS) developed in-house at New Mexico State University. The FF-TG-GC demonstrates the ability to separate a variety of nitroaromatic compounds of explosive significance in 20 s using a nitrogen carrier gas, highlighting the potential to offer selectivity advantages without substantially compromising high-throughput demands. These selectivity advantages are illustrated by the successful application of the FF-TG-GC-DMS-DMS to the detection and identification of single-nanogram loadings of 18 explosives and related substances in the presence of interfering materials, such as lactic acid, musk, and diesel. Furthermore, the system is capable of mitigating in-source ion-suppression effects by chromatographic separation of target analytes from background interference prior to ionization.

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.

Analysis of drugs including illicit and new psychoactive substances in oral fluids by gas chromatography-drift tube ion mobility spectrometry

In this study, a gas chromatograph (GC) has been coupled to a drift tube ion mobility spectrometer (IMS) in order to develop an analytical procedure for the determination of psychoactive substances in oral fluids. Working parameters, including the GC-IMS interface ones, were adjusted in order to obtain sensitive and robust signals. A volume of 500 μL of oral fluid was extracted with 250 μL chloroform and, after centrifugation, were injected into the GC-IMS system. Amphetamine, methylone, α-PVP, ketamine, lidocaine, MPHP, cocaine, THJ-2201, and 5F-ADB were employed as model compounds, providing limits of detection from 6 to 15 μg L^-1 and recoveries from 70 to 115% for field oral fluids spiked with target analytes at 250, 500, and 600 μg L^-1. Moreover, two oral fluid certified reference materials were analysed by the proposed GC-IMS based methodology with obtained relative percentage errors lower than 8.4%, being the proposed GC-IMS procedure a reliable, selective, and sensitive technique for the determination of psychoactive substances in oral fluids.

Improved selectivity for the determination of trinitrotoluene through reactive stage tandem ion mobility spectrometry and a quantitative measure of source-based suppression of ionization

A tandem ion mobility spectrometer was used to mobility isolate ions at the drift time for trinitrotoluene (TNT) in a first mobility stage, remove an interfering compound by ion decomposition in a middle reactive stage, and mobility characterize the remaining TNT ions in a second mobility stage. This sequential processing of ions provided decisive detection of TNT in the presence of an interfering peak differing from TNT in reduced mobility coefficient (K_o) by only 0.02 cm²/V. Even though ions of TNT (as M - 1)^- and the interfering compound were more than 90% convolved, TNT could be selectively detected with more than 95% decomposition of the interferent at 123 Td to an ion now separated by ΔK_o of 0.2 cm²/V from TNT. Ions for TNT were not decomposed in these electric fields though transmission efficiency was decreased by 20% through a wire grid assembly (the reactive stage). Although tandem ion mobility spectrometry with a reactive stage improves selectivity of measurement in the drift time dimension, the chemistry of ion formation in the ion source is affected still by ion suppression. Response to 1 ng TNT was decreased as much as 30% from 200 ng of interferent deposited on sample trap.

Quantitative response to nitrite from field-induced decomposition of the chloride adduct of RDX by reactive stage tandem ion mobility spectrometry

An additional dimension of selectivity for the determination of RDX by ion mobility spectrometry (IMS) was introduced through field-induced decomposition of RDX·Cl^- to NO₂^- on a spectral baseline free of interfering peaks. In this variant of reactive stage tandem IMS, the explosive ion is decomposed selectively in the presence of an interferent and from significantly convolved peaks which were mobility isolated within a narrow range of drift times using dual ion shutters. Field-induced decomposition at 170 °C and field strength of 112 Td (∼16 kV cm^-1) provided 15% decomposition yield and RDX, amid interferent, was detected decisively even when peaks differed in reduced mobility coefficients (K_o) by only 0.02 cm² V^-1 s^-1. A nitrite peak with S/N of 8.5 was observed with vapour concentrations of 54 ppb for RDX and 329 ppb for Interferent A in the ionization volume corresponding to 2 ng of RDX and 100 ng of Interferent A deposited on sample traps in the thermal desorption inlet. Findings on quantitative response suggest the presence of excessive amounts of interferent caused ionization suppression of RDX. Still, RDX was determined quantitatively using sequential processing of ions by mobility isolation, selective field induced decomposition, and mobility analysis in a second drift region.

Electrospray ionization rapid screening sans liquid chromatography column: A sensitive method for detection and quantification of chemicals in animal tissues and urine

RATIONALE

Electrospray ionization mass spectrometry (ESI-MS) in conjunction with liquid chromatography (LC) can provide accurate quantitative data, but it is not well-suited for the rapid screening (RS) of analytes incurred into complex matrices. This study was designed to determine the usefulness of ESI for rapid detection and quantitation of veterinary drugs from complex biological matrices under near real-time conditions.

METHODS

Nine veterinary drugs or metabolites, clenbuterol, erythromycin, flunixin, 5-hydroxyflunixin, meloxicam, ractopamine, salbutamol, tylosin and zilpaterol, present in cow urine, sheep urine, sheep tissues (kidney, muscle, liver and lung) or pig kidney, were simultaneously analyzed. A simple sample clean-up procedure, which included dilution with 10% sodium carbonate followed by extraction with ethyl acetate, was used. For tissues, an additional pre-extraction with hexane was performed to remove fat prior to MS analysis. Samples were introduced into the mass spectrometer through the LC autosampler, but no chromatographic separation was employed. A Sciex 5600+ triple time-of-flight mass spectrometer with a dual-spray source interfaced with a Shimadzu Nexera LC system was used. Samples were analyzed in positive ion mode.

RESULTS

Sample extraction times were typically 10-30 min or less and instrumental analysis time was 1 min/sample. Regression coefficients of matrix-matched standard curves across all compounds ranged from 0.9701-0.9999 in urine (cow and sheep) and tissues (sheep kidney, liver, lung, muscle and pig kidney). Limits of detection ranged from 0.11 to 2.03 ng/mL across analytes in urine and 0.11 to 8.86 ng/g across tissues. Correlations between RS-ESI-MS and LC/MS/MS results were 0.956 to 0.998 for incurred residues of flunixin in cow urine, ractopamine in pig kidney and zilpaterol in sheep urine.

CONCLUSIONS

RS-ESI-MS provided rapid, sensitive, and accurate analyses of nine veterinary drugs from complex matrices with very little sample preparation and produced quantitative data akin to LC/MS/MS.

Fast Detection of 2,4,6-Trinitrotoluene (TNT) at ppt Level by a Laser-Induced Immunofluorometric Biosensor

The illegal use of explosives by terrorists and other criminals is an increasing issue in public spaces, such as airports, railway stations, highways, sports venues, theaters, and other large buildings. Security in these environments can be achieved by different means, including the installation of scanners and other analytical devices to detect ultra-small traces of explosives in a very short time-frame to be able to take action as early as possible to prevent the detonation of such devices. Unfortunately, an ideal explosive detection system still does not exist, which means that a compromise is needed in practice. Most detection devices lack the extreme analytical sensitivity, which is nevertheless necessary due to the low vapor pressure of nearly all explosives. In addition, the rate of false positives needs to be virtually zero, which is also very difficult to achieve. Here we present an immunosensor system based on kinetic competition, which is known to be very fast and may even overcome affinity limitation, which impairs the performance of many traditional competitive assays. This immunosensor consists of a monolithic glass column with a vast excess of immobilized hapten, which traps the fluorescently labeled antibody as long as no explosive is present. In the case of the explosive 2,4,6-trinitrotoluene (TNT), some binding sites of the antibody will be blocked, which leads to an immediate breakthrough of the labeled protein, detectable by highly sensitive laser-induced fluorescence with the help of a Peltier-cooled complementary metal-oxide-semiconductor (CMOS) camera. Liquid handling is performed with high-precision syringe pumps and chip-based mixing-devices and flow-cells. The system achieved limits of detection of 1 pM (1 ppt) of the fluorescent label and around 100 pM (20 ppt) of TNT. The total assay time is less than 8 min. A cross-reactivity test with 5000 pM solutions showed no signal by pentaerythritol tetranitrate (PETN), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). This immunosensor belongs to the most sensitive and fastest detectors for TNT with no significant cross-reactivity by non-related compounds. The consumption of the labeled antibody is surprisingly low: 1 mg of the reagent would be sufficient for more than one year of continuous biosensor operation.

Assessing the Benefits and Costs of Homeland Security Research: A Risk-Informed Methodology with Applications for the U.S. Coast Guard

This article describes a methodology for risk-informed benefit-cost analyses of homeland security research products. The methodology is field-tested with 10 research products developed for the U.S. Coast Guard. Risk-informed benefit-cost analysis is a tool for risk management that integrates elements of risk analysis, decision analysis, and benefit-cost analysis. The cost analysis methodology includes a full-cost accounting of research projects, starting with initial fundamental research costs and extending to the costs of implementation of the research products and, where applicable, training, maintenance, and upgrade costs. The benefits analysis methodology is driven by changes in costs and risks leading to five alternative models: cost savings at the same level of security, increased security at the same cost, signal detection improvements, risk reduction by deterrence, and value of information. The U.S. Coast Guard staff selected 10 research projects to test and generalize the methodology. Examples include tools to improve the detection of explosives, reduce the costs of harbor patrols, and provide better predictions of hurricane wind speeds and floods. Benefits models and estimates varied by research project and many input parameters of the benefit estimates were highly uncertain, so risk analysis for sensitivity testing and simulation was important. Aggregating across the 10 research products, we found an overall median net present value of about $385 million, with a range from $54 million (5th percentile) to $877 million (95th percentile). Lessons learned are provided for future applications.

Utilizing Surface Acoustic Wave Nebulization (SAWN) for the Rapid and Sensitive Ambient Ionization Mass Spectrometric Analysis of Organic Explosives

When considering incident investigations and security checks focused on energetic materials, there is an ongoing need for rapid, on-scene chemical identification. Currently applied methods are not capable of meeting all requirements, and hence, portable mass spectrometry is an interesting alternative although many instrumental challenges still exist. To be able to analyze explosives with mass spectrometry outside the traditional laboratory, suitable ambient ionization methods need to be developed. Ideally such methods are also easily implemented in the field requiring limited to no power sources, gas supplies, flow controllers, and heating devices. For this reason, the potential of SAWN (surface acoustic wave nebulization) for the ambient ionization and subsequent mass spectrometric (MS) analysis of organic explosives was investigated in this study. Excellent sensitivity was observed for nitrate-based organic explosives when operating the MS in negative mode. No dominant adduct peaks were observed for the peroxides TATP and HMTD with SAWN-MS in positive mode. The MS spectra indicate extensive fragmentation of the peroxide explosives even under the mild ionization conditions provided by SAWN. The potential of SAWN-MS was demonstrated with the correct identification of nitrate-based organic explosives in pre- and post-explosion case samples in only a fraction of the time and effort required for the regular laboratory analysis. Results show that SAWN-MS can convincingly identify intact organic energetic compounds and mixtures but that sensitivity is not always sufficient to detect traces of explosives in post-explosion residues.

Atmospheric Solid Analysis Probe and Modified Desorption Electrospray Ionization Mass Spectrometry for Rapid Screening and Semi-Quantification of Zilpaterol in Urine and Tissues of Sheep

Ambient ionization mass spectrometric methods including desorption electrospray ionization (DESI) and atmospheric solid analysis probe (ASAP) have great potential for applications requiring real-time screening of target molecules in complex matrixes. Such techniques can also rapidly produce repeatable semiquantitative data, with minimal sample preparation, relative to liquid chromatography-mass spectrometry (LC-MS). In this study, a commercial ASAP probe was used to conduct both ASAP-MS and modified DESI (MDESI) MS analyses. We conducted real-time qualitative and semiquantitative analysis of the leanness-enhancing agent zilpaterol in incurred sheep urine, kidney, muscle, liver, and lung samples using ASAP-MS and MDESI MS. Using ASAP, limits of detection (LOD) and quantitation (LOQ) in urine were 1.1 and 3.7 ng/mL, respectively, while for MDESI MS they were 1.3 and 4.4 ng/mL, respectively. The LODs for tissues were 0.1-0.4 ng/g using ASAP, and 0.2-0.6 ng/g with MDESI MS. The LOQs of the tissues in ASAP were 0.4-1.2 ng/g and 0.5-2.1 ng/g in MDESI MS. Trace levels of zilpaterol were accurately analyzed in urine and tissues of sheep treated with dietary zilpaterol HCl. The correlation coefficient ( R²) between semiquantitative ASAP-MS and MDESI MS results of urine samples was 0.872. The data from ASAP and MDESI MS were validated using LC-MS/MS; urinary zilpaterol concentrations ≥5.0 ng/mL or tissue zilpaterol concentrations ≥1.5 ng/g were detected by ASAP and MDESI MS, respectively, 100% of the time. Forty samples could be analyzed in triplicate, directly from biological matrixes in under an hour.

Study of the adhesion of explosive residues to the finger and transfer to clothing and luggage

It is important to understand the extent of transfer of explosive particles to different surfaces in order to better evaluate potential cross-contamination by explosives in crowded security controls such as those at airports. This work investigated the transfer of nine explosive residues (ANFO, dynamite, black powder, TNT, HMTD, PETN, NH₄NO₃, KNO₃, NaClO₃) through fingerprints from one surface to another. First, the extent of adhesion of explosive residues from different surfaces to the bare finger, nitrile and latex gloves was studied. Then, the transfer of explosive residues from one surface to another through fingerprints was investigated. Cotton fabric (hereinafter referred to as cotton) as clothing material and polycarbonate plastic (hereinafter referred to as polycarbonate) as luggage material were chosen for the experiments. These surfaces containing explosive particles were imaged using a reflex camera before and after the particles were transferred. Afterwards the images were processed in MATLAB where pixels corresponding to explosive residues were quantified. Results demonstrated that transfer of explosive residues frequently occurred with certain differences among materials. Generally, the amount of explosive particles adhered to the finger decreased in the following order: skin>latex>nitrile, while the transfer of particles from the finger to another surface was the opposite. The adhesion of explosive residues from polycarbonate to the finger was found to be better compared to cotton, while the amount of particles transferred to cotton was higher.

Sorbent Film-Coated Passive Samplers for Explosives Vapour Detection Part B: Deployment in Semi-Operational Environments and Alternative Applications

The application of new sorbent-film coated passive samplers for capture of bulk commercial and military explosives vapours in operationally relevant spaces such as luggage, rooms, vehicles and shipping containers is presented. Samplers were easily integrated with in-service detection technologies with little/no sample preparation required. Ethylene glycol dinitrate (EGDN) was detected within 4 h in a container holding a suitcase packed with 0.2 kg Perunit 28E. Within a 22,000 dm³ room, 1 kg of concealed Seguridad was detected within 24 h and in an adjoining room within 7 days. Exposed samplers also successfully captured components of 1 kg TNT after 72 h and 1 kg concealed Perunit 28E after 6 h in both a furnished room and a large, partially filled shipping container. For the latter, samplers captured detectable residues outside the container after 24 h and were stable during wet weather for 72 h. A one-week trial at three operationally relevant venues including a university, a theatre and a government building revealed a nuisance positive rate of <1.4% (n = 72). Finally, two alternative applications are presented for extraction of liquid samples and use a particulate contact swab showing flexibility for a range of different search activities.

Ion Mobility Spectrometry - High Resolution LTQ-Orbitrap Mass Spectrometry for Analysis of Homemade Explosives

The detailed chemical characterization of homemade explosives (HMEs) and other chemicals that can mimic or mask the presence of explosives is important for understanding and improving the performance of commercial instrumentation used for explosive detection. To that end, an atmospheric-pressure drift tube ion mobility spectrometry (IMS) instrument has been successfully coupled to a commercial tandem mass spectrometry (MS) system. The tandem MS system is comprised of a linear ion trap and a high resolution Orbitrap analyzer. This IMS-MS combination allows extensive characterization of threat chemical compounds, including HMEs, and complex real-world background chemicals that can interfere with detection. Here, the composition of ion species originating from a specific HME, erythritol tetranitrate, has been elucidated using accurate mass measurements, isotopic ratios, and tandem MS. Gated IMS-MS and high-resolution MS have been used to identify minor impurities that can be indicative of the HME source and/or synthesis route. Comparison between data obtained on the IMS/MS system and on commercial stand-alone IMS instruments used as explosive trace detectors (ETDs) has also been performed. Such analysis allows better signature assignments of threat compounds, modified detection algorithms, and improved overall ETD performance. Graphical Abstract ᅟ.

Chemical Sniffing Instrumentation for Security Applications

Border control for homeland security faces major challenges worldwide due to chemical threats from national and/or international terrorism as well as organized crime. A wide range of technologies and systems with threat detection and monitoring capabilities has emerged to identify the chemical footprint associated with these illegal activities. This review paper investigates artificial sniffing technologies used as chemical sensors for point-of-use chemical analysis, especially during border security applications. This article presents an overview of (a) the existing available technologies reported in the scientific literature for threat screening, (b) commercially available, portable (hand-held and stand-off) chemical detection systems, and (c) their underlying functional and operational principles. Emphasis is given to technologies that have been developed for in-field security operations, but laboratory developed techniques are also summarized as emerging technologies. The chemical analytes of interest in this review are (a) volatile organic compounds (VOCs) associated with security applications (e.g., illegal, hazardous, and terrorist events), (b) chemical "signatures" associated with human presence, and

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.

Development and validation of an isotope dilution ultra-high performance liquid chromatography tandem mass spectrometry method for the reliable quantification of 1,3,5-Triamino-2,4,6-trinitrobenzene (TATB) and 14 other explosives and their degradation products in environmental water samples

A comprehensive method for the determination and characterization of 15 common explosive compounds in water samples by ultra-high pressure liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (APCI-MS/MS) is presented. The method allows the determination of 10 nitroaromatics, two nitroamines and three nitrate ester compounds. Among these, 1,3,5-Triamino-2,4,6-trinitrobenzene (TATB) was quantified and detected for the first time in our knowledge at trace levels (0.2 µg/L). Furthermore, the collision induced dissociation (CID) mass spectrum of TATB is discussed and a fragmentation mechanism is proposed. The signal for each explosive was normalized by isotopically-enriched congeners used as internal standards. The limits of detection (LOD) reached 20 ng/L, depending on the type of energetic molecule, which are adequate for water samples and the linearity was verified from 1.4 to 2 orders of magnitude. The sensitivity of the UHPLC-APCI-MS/MS approach allows direct injection of aqueous samples without preceding extraction for concentration. Besides, the method displays a good reliability with low signal suppression in various matrices such as spring water, mineral water, acidified water or ground water. The effectiveness of the method is demonstrated by the analysis of underground water samples containing traces of explosives from test fields in France.

Portable solid phase micro-extraction coupled with ion mobility spectrometry system for on-site analysis of chemical warfare agents and simulants in water samples

On-site analysis is an efficient approach to facilitate analysis at the location of the system under investigation as it can result in more accurate, more precise and quickly available analytical data. In our work, a novel self-made thermal desorption based interface was fabricated to couple solid-phase microextraction with ion mobility spectrometry for on-site water analysis. The portable interface can be connected with the front-end of an ion mobility spectrometer directly without other modifications. The analytical performance was evaluated via the extraction of chemical warfare agents and simulants in water samples. Several parameters including ionic strength and extraction time have been investigated in detail. The application of the developed method afforded satisfactory recoveries ranging from 72.9% to 114.4% when applied to the analysis of real water samples.