Elucidating the Gas-Phase Behavior of Nitazene Analog Protomers Using Structures for Lossless Ion Manipulations Ion Mobility-Orbitrap Mass Spectrometry.

2-Benzylbenzimidazoles, or "nitazenes", are a class of novel synthetic opioids (NSOs) that are increasingly being detected alongside fentanyl analogs and other opioids in drug overdose cases. Nitazenes can be 20× more potent than fentanyl but are not routinely tested for during postmortem or clinical toxicology drug screens; thus, their prevalence in drug overdose cases may be under-reported. Traditional analytical workflows utilizing liquid chromatography-tandem mass spectrometry (LC-MS/MS) often require additional confirmation with authentic reference standards to identify a novel nitazene. However, additional analytical measurements with ion mobility spectrometry (IMS) may provide a path toward reference-free identification, which would greatly accelerate NSO identification rates in toxicology laboratories. Presented here are the first IMS and collision cross section (CCS) measurements on a set of fourteen nitazene analogs using a structures for lossless ion manipulations (SLIM)-orbitrap MS. All nitazenes exhibited two high intensity baseline-separated IMS distributions, which fentanyls and other drug and druglike compounds also exhibit. Incorporating water into the electrospray ionization (ESI) solution caused the intensities of the higher mobility IMS distributions to increase and the intensities of the lower mobility IMS distributions to decrease. Nitazenes lacking a nitro group at the R1 position exhibited the greatest shifts in signal intensities due to water. Furthermore, IMS-MS/MS experiments showed that the higher mobility IMS distributions of all nitazenes possessing a triethylamine group produced fragment ions with m/z 72, 100, and other low intensity fragments while the lower mobility IMS distributions only produced fragment ions with m/z 72 and 100. The IMS, solvent, and fragmentation studies provide experimental evidence that nitazenes potentially exhibit three gas-phase protomers. The cyclic IMS capability of SLIM was also employed to partially resolve four sets of structurally similar nitazene isomers (e.g., protonitazene/isotonitazene, butonitazene/isobutonitazene/secbutonitazene), showcasing the potential of using high-resolution IMS separations in MS-based workflows for reference-free identification of emerging nitazenes and other NSOs.

Identification of Unique Fragmentation Patterns of Fentanyl Analog Protomers Using Structures for Lossless Ion Manipulations Ion Mobility-Orbitrap Mass Spectrometry.

The opioid crisis in the United States is being fueled by the rapid emergence of new fentanyl analogs and precursors that can elude traditional library-based screening methods, which require data from known reference compounds. Since reference compounds are unavailable for new fentanyl analogs, we examined if fentanyls (fentanyl + fentanyl analogs) could be identified in a reference-free manner using a combination of electrospray ionization (ESI), high-resolution ion mobility (IM) spectrometry, high-resolution mass spectrometry (MS), and higher-energy collision-induced dissociation (MS/MS). We analyzed a mixture containing nine fentanyls and W-15 (a structurally similar molecule) and found that the protonated forms of all fentanyls exhibited two baseline-separated IM distributions that produced different MS/MS patterns. Upon fragmentation, both IM distributions of all fentanyls produced two high intensity fragments, resulting from amine site cleavages. The higher mobility distributions of all fentanyls also produced several low intensity fragments, but surprisingly, these same fragments exhibited much greater intensities in the lower mobility distributions. This observation demonstrates that many fragments of fentanyls predominantly originate from one of two different gas-phase structures (suggestive of protomers). Furthermore, increasing the water concentration in the ESI solution increased the intensity of the lower mobility distribution relative to the higher mobility distribution, which further supports that fentanyls exist as two gas-phase protomers. Our observations on the IM and MS/MS properties of fentanyls can be exploited to positively differentiate fentanyls from other compounds without requiring reference libraries and will hopefully assist first responders and law enforcement in combating new and emerging fentanyls.

Standoff trace explosives vapor detection at meter distances.

Vapor detection is a noncontact sampling method, which is a less invasive means of explosives screening than physical swiping. Explosive vapor detection is a challenge due to the low levels of vapors available for detection. This study demonstrates that the parts-per-quadrillion sensitivity of atmospheric flow tube-mass spectrometry (AFT-MS) combined with a high-volume air sampler enables standoff detection of trace explosives vapor at distances of centimeters to meters. Standoff detection of explosives vapor was possible both upstream and downstream of the vapor source relative to room air currents. RDX vapor from a saturated source was detected at up to 2.5 m. Vapors from RDX residue and nitroglycerin residue were detected at distances up to 0.5 m. The sampling can be optimized by accounting for air movement in the room or environment, which could further extend standoff detection distances. Using AFT-MS with a high-volume sampler could also be effective for standoff vapor detection of drugs and additional chemical threats and could be useful for security screening applications such as at mail facilities, border crossings, and security checkpoints.

A Dual-Gated Structures for Lossless Ion Manipulations-Ion Mobility Orbitrap Mass Spectrometry Platform for Combined Ultra-High-Resolution Molecular Analysis.

High-resolution ion mobility spectrometry-mass spectrometry (HR-IMS-MS) instruments have enormously advanced the ability to characterize complex biological mixtures. Unfortunately, HR-IMS and HR-MS measurements are typically performed independently due to mismatches in analysis time scales. Here, we overcome this limitation by using a dual-gated ion injection approach to couple an 11 m path length structures for lossless ion manipulations (SLIM) module to a Q-Exactive Plus Orbitrap MS platform. The dual-gate setup was implemented by placing one ion gate before the SLIM module and a second ion gate after the module. The dual-gated ion injection approach allowed the new SLIM-Orbitrap platform to simultaneously perform an 11 m SLIM separation, Orbitrap mass analysis using the highest selectable mass resolution setting (up to 140 k), and high-energy collision-induced dissociation (HCD) in ∼25 min over an m/z range of ∼1500 amu. The SLIM-Orbitrap platform was initially characterized using a mixture of standard phosphazene cations and demonstrated an average SLIM CCS resolving power (RpCCS) of ∼218 and an SLIM peak capacity of ∼156, while simultaneously obtaining high mass resolutions. SLIM-Orbitrap analysis with fragmentation was then performed on mixtures of standard peptides and two reverse peptides (SDGRG1+, GRGDS1+, and RpCCS = 305) to demonstrate the utility of combined HR-IMS-MS/MS measurements for peptide identification. Our new HR-IMS-MS/MS capability was further demonstrated by analyzing a complex lipid mixture and showcasing SLIM separations on isobaric lipids. This new SLIM-Orbitrap platform demonstrates a critical new capability for proteomics and lipidomics applications, and the high-resolution multimodal data obtained using this system establish the foundation for reference-free identification of unknown ion structures.

Vapor detection and vapor pressure measurements of fentanyl and fentanyl hydrochloride salt at ambient temperatures.

There is a need for non-contact, real-time vapor detection of drugs to combat illicit transportation and help curb the opioid epidemic. The low volatility of drugs, like fentanyl, makes room temperature vapor detection of illicit drugs challenging, but feasible by atmospheric flow tube-mass spectrometry (AFT-MS). AFT-MS is a non-contact vapor detection approach capable of ultra-trace detection of drugs, including fentanyl and its analogs at low parts-per-quadrillion (ppqv) levels. The determination of vapor pressure values of fentanyl is necessary to understand potential vapor concentrations that may be available for detection. In this paper, vapor pressures of fentanyl free base and fentanyl hydrochloride salt (a common form of the illicit drug) were measured as a function of temperature at or near ambient conditions using the transpiration (gas saturation) method and AFT-MS. Based on our measurements, the vapor pressure of fentanyl at 25 °C is 9.0 × 10-14 atm (90 ppqv), and the vapor pressure of fentanyl hydrochloride at 25 °C is 1.8 × 10-17 atm (0.018 ppqv). We also demonstrate non-contact, real-time vapor detection of fentanyl. Preconcentration of vapors can further extend the detection capabilities. The collection, desorption, and detection of fentanyl vapors at ambient conditions was demonstrated for sampling times of seconds to an hour resulting in increased signal. AFT-MS is a viable detection method of fentanyl and other drugs for screening of packages and cargo.

Proton Affinity Values of Fentanyl and Fentanyl Analogues Pertinent to Ambient Ionization and Detection.

Proton affinity is a major factor in the atmospheric pressure chemical ionization of illicit drugs. The detection of illicit drugs by mass spectrometry and ion mobility spectrometry relies on the analytes having greater proton affinities than background species. Evaluating proton affinities for fentanyl and its analogues is informative for predicting the likelihood of ionization in different environments and for optimizing the compounds' ionization and detection, such as through the addition of dopant chemicals. Herein, density functional theory was used to computationally determine the proton affinity and gas-phase basicity of 15 fentanyl compounds and several relevant molecules as a reference point. The range of proton affinities for the fentanyl compounds was from 1018 to 1078 kJ/mol. Fentanyl compounds with the higher proton affinity values appeared to form a bridge between the oxygen on the amide and the protonated nitrogen on the piperidine ring based on models and calculated bond distances. Experiments with fragmentation of proton-bound clusters using atmospheric flow tube-mass spectrometry (AFT-MS) provided estimates of relative proton affinities and showed proton affinity values of fentanyl compounds >1000 kJ/mol, which were consistent with the computational results. The high proton affinities of fentanyl compounds facilitate their detection by ambient ionization techniques in complex environments. The detection limits of the fentanyl compounds with AFT-MS are in the low femtogram range, which demonstrates the feasibility of trace vapor drug detection.

Trace explosive residue detection of HMX and RDX in post-detonation dust from an open-air environment.

Explosives are often used in industry, geology, mining, and other applications, but it is not always clear what remains after a detonation or the fate and transport of any residual material. The goal of this study was to determine to what extent intact molecules of high explosive (HE) compounds are detectable and quantifiable from post-detonation dust and particulates in a field experiment with varied topography. We focused on HMX (1,3,5,7-Tetranitro-1,3,5,7-tetrazocane), which is less studied in field detonation literature, as the primary explosive material and RDX (1,3,5-Trinitroperhydro-1,3,5-triazine) as the secondary material. The experiment was conducted at Site 300, Lawrence Livermore National Laboratory's Experimental Test Site, in California, USA. Two 20.4 kg and one 40.8 kg above ground explosions (primarily comprised of LX-14, an HMX-based polymer-bonded high explosive) were detonated on an open-air firing area on separate days. The complex terrain of the firing area (e.g., buildings, berm, low-height obstacles) was advantageous to study HE deposition in relation to plume dynamics. Three types of samples were collected up to 100 m away from each shot: surface swipes of aluminum plates, surface swipes of fixed objects, and filters from air samples. We used atmospheric flow tube-mass spectrometry (AFT-MS) to quantify picogram levels of molecular residue of HE material in the post-detonation dust. An aliquot of sample extract in methanol (e.g., 1 µL of 0.5 mL) was placed onto a resistive material and then thermally desorbed into the AFT-MS. We successfully detected and quantified both HMX and RDX in many of the samples. Based on mass (pg) detected and solution dilution, we back-calculated the mass collected on the swipe or filter (ng per sample). The aerial distribution of molecular residue was consistent with the path of the plume, which was strongly determined by wind speed and direction at the time of each shot. The quantity of material detected appeared to correlate more with distance from the shot and the wind conditions than with shot size. This study demonstrates that the picogram detection levels of AFT-MS are well-suited for quantification of analytes (e.g., HMX and RDX) in environmental samples.

Vapor Pressures of RDX and HMX Explosives Measured at and Near Room Temperature: 1,3,5-Trinitro-1,3,5-triazinane and 1,3,5,7-Tetranitro-1,3,5,7-tetrazocane.

Knowing accurate saturated vapor pressures of explosives at ambient conditions is imperative to provide realistic boundaries on available vapor for ultra-trace detection. In quantifying vapor content emanating from low-volatility explosives, we observed discrepancies between the quantity of explosive expected based on literature vapor pressure values and the amount detected near ambient temperatures. Most vapor pressure measurements for low-volatility explosives, such as RDX (1,3,5-trinitro-1,3,5-triazinane) and HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane), have been made at temperatures far exceeding 25 °C and linear extrapolation of these higher temperature trends appears to underestimate vapor pressures near room temperature. Our goal was to measure vapor pressures as a function of temperature closer to ambient conditions. We used saturated RDX and HMX vapor sources at controlled temperatures to produce vapors that were then collected and analyzed via atmospheric flow tube-mass spectrometry (AFT-MS). The parts-per-quadrillion (ppqv) sensitivity of AFT-MS enabled measurement of RDX vapor pressures at temperatures as low as 7 °C and HMX vapor pressures at temperatures as low as 40 °C for the first time. Furthermore, these vapor pressures were corroborated with analysis of vapor generated by nebulizing low concentration solutions of RDX and HMX. We report updated vapor pressure values for both RDX and HMX. Based on our measurements, the vapor pressure of RDX at 25 °C is 3 ± 1 × 10-11 atm (i.e., 30 parts per trillion by volume, pptv), the vapor pressure of HMX is 1.0 ± 0.6 × 10-14 atm (10 ppqv) at 40 °C and, with extrapolation, HMX has a vapor pressure of 1.0 ± 0.6 × 10-15 atm (1.0 ppqv) at 25 °C.

Non-contact vapor detection of illicit drugs via atmospheric flow tube-mass spectrometry.

Real-time, non-contact detection of illicit drugs is a desirable goal for the interdiction of these controlled substances, but the relatively low vapor pressures of such species present a challenge for trace vapor detection technologies. The introduction of atmospheric flow tube-mass spectrometry (AFT-MS), which has previously been demonstrated to detect gas-phase analytes at low parts-per-quadrillion levels for explosives and organophosphorus compounds, also enables the potential for non-contact drug detection. With AFT-MS, direct vapor detection of cocaine and methamphetamine from ∼5 µg residues at room temperature is demonstrated herein. Furthermore, thermal desorption of low- to sub-picogram levels of cocaine, methamphetamine, fentanyl, and heroin is observed via AFT-MS using a carrier flow rate of several L min-1 of air. These low levels can permit non-contact sampling through collection of vapor, effectively preconcentrating the analyte before desorption and analysis. Quantitative evaluation of the thermal desorption approach has yielded limits of detection (LODs) on the order of 10 fg for cocaine and fentanyl, 100 fg for methamphetamine, and 1.6 pg for heroin. The LOD for heroin was lowered to 300 fg by using tributyl phosphate as a dopant to form a proton-bound heterodimer with heroin. When used with AFT-MS, the intentional formation of specific drug-dopant adducts has the potential to enhance detection limits and selectivity of additional drug species. Species that are prone to form adducts present a challenge to analysis, but that difficulty can be overcome by the intentional addition of a dopant. Molecules unlikely to form adducts will remain essentially unimpacted, but the adduct-forming species will interact with the dopant to compress the analyte signal into a single peak. This approach would be valuable in the application of non-contact screening for illicit substances via vapor collection followed by thermal desorption for analysis.

Ambient vapor sampling and selective cluster formation for the trace detection of tributyl phosphate via atmospheric flow tube mass spectrometry.

In addition to serving as an f-element ligand and rare-earth method complexing agent, tributyl phosphate is a compound containing core functional groups that mimic those routinely found in degradation products from industrial processes. Because detection of trace quantities of tributyl phosphate can provide insight into the routes of contamination and degradation in the environment, there is a need to develop methods capable of detecting trace quantities of tributyl phosphate. Vapor detection at atmospheric pressure is one approach that is both sensitive and rapid. We present here the use of atmospheric flow tube mass spectrometry for the ambient vapor sampling of tributyl phosphate from headspace of ppb-level solutions in methanol. Gas phase clustering reactions were to enhance detection levels via the addition of small quantities of the dopants diethylamine, triethylamine, and pinacolyl methylphosphonate in the vapor stream. Detection of the tributyl phosphate vapor emanating from these solutions demonstrated a linear range for the protonated tributyl phosphate species of 1-1000 ppb from solution. The clusters of tributyl phosphate with diethylamine, triethylamine, and pinacolyl phosphonate each yielded linear ranges of 1-250 ppb for tributyl phosphate in solution. Despite smaller linear ranges, the addition of these dopant species added a layer of analytical selectivity and reduced variability in signals from quality control samples. These data were obtained using an atmospheric flow tube source coupled to a linear ion trap mass spectrometer, which demonstrates the applicability of trapping systems to the atmospheric flow tube ionization technique while monitoring positive ions.

Detection of Inorganic Salt-Based Homemade Explosives (HME) by Atmospheric Flow Tube-Mass Spectrometry.

Using a commercial mass spectrometer interfaced with an atmospheric flow tube (AFT) allowed for the detection of a variety of inorganic compounds used as oxidizers in homemade explosives (HMEs) at picogram levels. The AFT provides reaction times of between 3 and 5 s with flows of 6 L/min, enabling detection levels, after thermal desorption, similar to those previously demonstrated for RDX vapor in the low parts per quadrillion range. The thermal desorption of chlorate and perchlorate salts resulted in the production of the corresponding anions which have higher electron affinities than that of the nitrate reactant ions. A dielectric barrier discharge, used as the ionization source, produced the nitrate reactant ions. In some instances, the molecular salt formed adducts with the nitrate, chlorate, and/or perchlorate anions, giving insight into the original identity of the salt cation. Urea nitrate, guanidine nitrate, and potassium nitrate were also detected as adducts with the nitrate reactant ion. The direct room-temperature vapor detection of urea nitrate and hydrogen peroxide, which have relatively high vapor pressures compared to the other salts in this study, is also demonstrated. Room-temperature vapor detection of chlorate and perchlorate salts is possible by the addition of a dilute acid which converts the salt into a more volatile acidic form. A discussion of the instrumentation, methods used, and the ionization chemistry is provided.

Selective Reagent Ions for the Direct Vapor Detection of Organophosphorus Compounds Below Parts-per-Trillion Levels.

Real-time low to sub parts-per-trillion (pptv) vapor detection of some organophosphorous compounds (OPCs) is demonstrated with an atmospheric flow tube-mass spectrometer. The chemical species investigated included dimethyl methylphosphonate, triethyl phosphate, and tributylphosphate. The atmospheric flow tube provides ambient chemical ionization with up to several seconds of ionization time. With sensitivities in the parts-per-quadrillion (ppqv) range, there are many background contaminants competing for charge with the target analytes. Initially, the OPCs were not observable in direct room air analysis, presumably due to other trace components possessing higher proton affinities. However, the addition of a trialkylamine as a dopant chemical served to provide a single reagent ion that also formed a proton-bound heterodimer with the OPCs. These asymmetric proton-bound dimers had sufficiently high hydrogen bond energy to allow the cluster to remain intact during the analysis time of several seconds. Changes in stability were observed for some of these asymmetric proton-bound dimers with a shorter half-life for adducts with a larger proton affinity differences between the amine and the OPC. Detection levels approaching low pptv to high ppqv were correlated by three different methods, including use of a permeation tube, direct injection of a fixed mass into the sample air flow, and calculations based upon signal intensity ratios, reaction time, and an estimated reaction rate constant. A practical demonstration showed real-time monitoring of a laboratory environment initially with low pptv levels of vapor observed to decay exponentially over about an hour while returning to baseline levels.

A Hybrid Constant and Oscillatory Field Ion Mobility Analyzer Using Structures for Lossless Ion Manipulations.

Here we explore the combination of constant and oscillatory fields applied in a single device to affect the continuous separation and filtering of ions based on their mobilities. The device explored allows confining and manipulating ions utilizing a combination of radio frequency (rf), direct current (DC) fields, and traveling waves (TW) in a structures for lossless ion manipulations (SLIM) module. We have investigated theoretically and experimentally a concept for continuous filtering of ions based on their mobilities where ions are mobility separated and selected by passage through two regions, both of which incorporated combined TW and constant fields providing opposing forces on the ions. The SLIM module was composed of two surfaces with mirror-image arrays of electrodes and had two regions where the different TW and opposing DC fields could be applied. The filtering capabilities are determined by the applied DC gradient and the TW parameters, such as speed, amplitude, and the TW sequence (i.e., the duty cycle of the traveling wave). The effects of different parameters on the sensitivity and the ion mobility (IM) resolution of the device have been investigated. By appropriately choosing the DC gradient and TW parameters for the two sections, it is possible to transmit ions of a selected mobility while filtering out others of both higher and lower mobility. The novel device described here provides a basis for the targeted analysis of compounds based upon the continuous selection of ions according to their mobility and without the need for high electric fields or pulsed injection. Graphical abstract ᅟ.

Bayesian Integration and Classification of Composition C-4 Plastic Explosives Based on Time-of-Flight-Secondary Ion Mass Spectrometry and Laser Ablation-Inductively Coupled Plasma Mass Spectrometry.

Time-of-flight-secondary ion mass spectrometry (TOF-SIMS) and laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) were used for characterization and identification of unique signatures from a series of 18 Composition C-4 plastic explosives. The samples were obtained from various commercial and military sources around the country. Positive and negative ion TOF-SIMS data were acquired directly from the C-4 residue on Si surfaces, where the positive ion mass spectra obtained were consistent with the major composition of organic additives, and the negative ion mass spectra were more consistent with explosive content in the C-4 samples. Each series of mass spectra was subjected to partial least squares-discriminant analysis (PLS-DA), a multivariate statistical analysis approach which serves to first find the areas of maximum variance within different classes of C-4 and subsequently to classify unknown samples based on correlations between the unknown data set and the original data set (often referred to as a training data set). This method was able to successfully classify test samples of C-4, though with a limited degree of certainty. The classification accuracy of the method was further improved by integrating the positive and negative ion data using a Bayesian approach. The TOF-SIMS data was combined with a second analytical method, LA-ICPMS, which was used to analyze elemental signatures in the C-4. The integrated data were able to classify test samples with a high degree of certainty. Results indicate that this Bayesian integrated approach constitutes a robust classification method that should be employable even in dirty samples collected in the field.

Optimizing detection of RDX vapors using designed experiments for remote sensing.

This paper presents results of designed experiments performed to study the effect of four factors on the detection of RDX vapors from desorption into an atmospheric flow tube mass spectrometer (AFT-MS). The experiments initially included four independent factors: gas flow rate, desorption current, solvent evaporation time and RDX mass. The values of three detection responses, peak height, peak width, and peak area were recorded but only the peak height response was analyzed. Results from the first block of experiments indicated that solvent evaporation time was not statistically significant at the 95% confidence level. A second round of experiments was designed and executed using flow rate, current, and RDX mass as factors and the results were used to create a model to predict conditions resulting in maximum peak height. Those conditions were confirmed experimentally and used to obtain data for a calibration model. The calibration model represented RDX amounts ranging from 1 to 25 pg desorbed into an air flow of 7 L min(-1). Air samples from a shipping container that held 2 closed explosive storage magazines were collected on metal filaments for varying amounts for time ranging from 5 to 90 minutes. RDX was detected from all of the filaments sampled by desorption into the AFT-MS. From the calibration model, RDX vapor concentrations within the shipping container were calculated to be in the range of 1 to 50 parts-per-quadrillion (ppqv) from data collected on 2 separate days.

Direct real-time detection of vapors from explosive compounds.

The real-time detection of vapors from low volatility explosives including PETN, tetryl, RDX, and nitroglycerine along with various compositions containing these substances was demonstrated. This was accomplished with an atmospheric flow tube (AFT) using a nonradioactive ionization source coupled to a mass spectrometer. Direct vapor detection was accomplished in less than 5 s at ambient temperature without sample preconcentration. The several seconds of residence time of analytes in the AFT provided a significant opportunity for reactant ions to interact with analyte vapors to achieve ionization. This extended reaction time, combined with the selective ionization using the nitrate reactant ions (NO3(-) and NO3(-)·HNO3), enabled highly sensitive explosives detection from explosive vapors present in ambient laboratory air. Observed signals from diluted explosive vapors indicated detection limits below 10 ppqv using selected ion monitoring (SIM) of the explosive-nitrate adduct at m/z 349, 378, 284, and 289 for tetryl, PETN, RDX, and NG, respectively. Also provided is a demonstration of the vapor detection from 10 different energetic formulations sampled in ambient laboratory air, including double base propellants, plastic explosives, and commercial blasting explosives using SIM for the NG, PETN, and RDX product ions.

Direct real-time detection of RDX vapors under ambient conditions.

The results in this manuscript represent a demonstration of RDX vapor detection in real time at ambient temperature without sample preconcentration. The detection of vapors from the low volatility explosive compound RDX was achieved through selective atmospheric pressure chemical ionization using nitrate reactant ions (NO(3)(-)) and NO(3)(-)·HNO(3) adducts generated in an electrical discharge source. The RDX vapors were ionized in a reaction region, which provided a variable (up to several seconds) reaction time. The reaction times were controlled either by flow in an atmospheric flow tube (AFT) or by an electric field in an atmospheric drift tube (ADT). Both AFT and ADT were interfaced to a quadrupole mass spectrometer for ion detection and identification. Recorded signals were observed for RDX concentrations below 25 ppq using selected ion monitoring (SIM) of the RDX-nitrate adduct at m/z 284.

Photoemission ambient pressure ionization (PAPI) with an ultraviolet light emitting diode and detection of organic compounds.

The development of compact, rugged and low-power ion sources is critical for the further advancement of handheld mass analyzers. Further, there is a need to replace the common (63)Ni source used at atmospheric pressure with a non-radioactive substitute. We present here a description of a light emitting diode (LED) photoemission ionization source for use in mass spectrometry for the detection of volatile organic compounds. This technique relies upon the generation of photoelectrons from a low-work function metal via low-energy ultraviolet (UV) light (280 or 240 nm) generated by a single LED in air at atmospheric pressure. These low-energy photoelectrons result in either direct electron capture by the analyte or chemical ionization. Currently, only negative ions are demonstrated due to operation at atmospheric pressure. Ion generation occurs without use of high electric fields such as those found in corona discharge or electrospray ionization. This source is effective for measuring organic vapors from gases, liquids and surface residues via atmospheric pressure chemical ionization, initiated by photoemission off a conductive surface. Several classes of organic vapors are analyzed and found to be effectively detected, including compounds that ionize via electron attachment, dissociative electron capture, proton abstraction, adduct formation and replacement ionization.

Characterization of triacetone triperoxide by ion mobility spectrometry and mass spectrometry following atmospheric pressure chemical ionization.

The atmospheric pressure chemical ionization of triacetone triperoxide (TATP) with subsequent separation and detection by ion mobility spectrometry has been studied. Positive ionization with hydronium reactant ions produced only fragments of the TATP molecule, with m/z 91 ion being the most predominant species. Ionization with ammonium reactant ions produced a molecular adduct at m/z 240. The reduced mobility value of this ion was constant at 1.36 cm(2)V(-1)s(-1) across the temperature range from 60 to 140 °C. The stability of this ion was temperature dependent and did not exist at temperatures above 140 °C, where only fragment ions were observed. The introduction of ammonia vapors with TATP resulted in the formation of m/z 58 ion. As the concentration of ammonia increased, this smaller ion appeared to dominate the spectra and the TATP-ammonium adduct decreased in intensity. The ion at m/z 58 has been noted by several research groups upon using ammonia reagents in chemical ionization, but the identity was unknown. Evidence presented here supports the formation of protonated 2-propanimine. A proposed mechanism involves the addition of ammonia to the TATP-ammonium adduct followed by an elimination reaction. A similar mechanism involving the chemical ionization of acetone with excess ammonia also showed the formation of m/z 58 ion. TATP vapors from a solid sample were detected with a hand-held ion mobility spectrometer operated at room temperature. The TATP-ammonium molecular adduct was observed in the presence of ammonia and TATP vapors with this spectrometer.