Ion Mobility–Mass Spectrometry Using a Dual-Gated 3D Printed Ion Mobility Spectrometer

Dependency of fentanyl analogue protomer ratios on solvent conditions as measured by ion mobility-mass spectrometry

Recently, our group has shown that fentanyl and many of its analogues form prototropic isomers ("protomers") during electrospray ionization. These different protomers can be resolved using ion mobility spectrometry and annotated using mobility-aligned tandem mass spectrometry fragmentation. However, their formation and the extent to which experimental variables contribute to their relative ratio remain poorly understood. In the present study, we systematically investigated the effects of mixtures of common chromatographic solvents (water, methanol, and acetonitrile) and pH on the ratio of previously observed protomers for 23 fentanyl analogues. Interestingly, these ratios (N-piperidine protonation vs. secondary amine/O = protonation) decreased significantly for many analogues (e.g., despropionyl ortho-, meta-, and para-methyl fentanyl), increased significantly for others (e.g., cis-isofentanyl), and remained relatively constant for the others as solvent conditions changed from 100% organic solvent (methanol or acetonitrile) to 100% water. Interestingly, pH also had significant effects on this ratio, causing the change in ratio to switch in many cases. Lastly, increasing conditions to pH ≥ 4.0 also prompted the appearance of new mobility peaks for ortho- and para-methyl acetyl fentanyl, where all previous studies had only showed one single distribution. Because these ratios have promise to be used qualitatively for identification of these (and emerging) fentanyl analogues, understanding how various conditions (i.e., mobile phase selection and/or chromatographic gradient) affect their ratios is critically important to the development of advanced ion mobility and mass spectrometry methodologies to identify fentanyl analogues.

Enhancing the Performance of Tyndall-Powell Gate Ion Mobility Spectrometry by Combining Ion Enrichment, Discrimination Reduction, and Temporal Compression into a Single Gating Process

The broad applications of ion mobility spectrometry (IMS) demand good sensitivity and resolving power for ion species with different reduced mobilities (K0). In this work, a new Tyndall-Powell gate (TPG) gating method for combining ion enrichment, mobility discrimination reduction, and temporal compression into a single gating process is proposed to improve IMS analysis performance. The two-parallel-grid structure and well-confined gate region of the TPG make it convenient to spatiotemporally vary the electric fields within and around the gate region. Under the new gating method, a potential wave is applied on TPG grid 1 to enrich ions within the ionization region adjacent to the TPG during the gate-closed state; meanwhile, a potential wave is applied on TPG grid 2 to enhance mobility discrimination reduction and temporal compression simultaneously during the gate-open state. For triethyl phosphate (TEP) and dimethyl methylphosphonate mixtures, product ion peaks within K0 of 1.9 to 1.1 cm2/V·s exhibit a 19-fold increase in ion current compared to the traditional TPG gating method, while maintaining a resolving power of 85. The estimated limit of detection for the TEP dimer is lowered from 8 ppb to 135 ppt. The new gating method can be applied to other TPG-based IMS systems to enhance their performance in analyzing complex samples.

Development of a Modular, Open-Source, Reduced-Pressure, Drift Tube Ion Mobility Spectrometer

Toward the goal of minimizing construction costs while maintaining high performance, a new, reduced-pressure, drift tube ion mobility system is coupled with an ion trap mass analyzer through a custom ion shuttle. The availability of reduced-pressure ion mobility systems remains limited due to comparatively expensive commercial options and limited shared design features in the open literature. This report details the complete design and benchmarking characteristics of a reduced-pressure ion mobility system. The system is constructed from FR4 PCB electrodes and encased in a PTFE vacuum enclosure with custom torque-tightened couplers to utilize standard KF40 bulkheads. The PTFE enclosure directly minimizes the overall system expenses, and the implementation of threaded brass inserts allows for facile attachments to the vacuum enclosure without damaging the thermoplastic housing. Front and rear ion funnels maximize ion transmission and help mitigate the effects of radial ion diffusion. A custom planar ion shuttle transports ions from the exit of the rear ion funnel into the ion optics of an ion trap mass analyzer. The planar ion shuttle can couple the IM system to any contemporary Thermo Scientific ion trap mass analyzer. Signal stability and ion intensity remain unchanging following the implementation of the planar ion shuttle when compared to the original stacked ring ion guide. The constructed IM system showed resolving powers up to 85 for various small molecules and proteins using the Fourier transform from a ∼1 m drift tube. Recorded mobilities derived from first principles agree with published literature results with an average error of 1.1% and an average error toward literature values using single field calibration of <1.3%.

Improved separation of fentanyl isomers using metal cation adducts and high-resolution ion mobility-mass spectrometry

Fentanyl is a potent synthetic opioid that has attracted significant attention due to its illegal production and distribution, resulting in misuse, overdose, and fatalities. Because numerous fentanyl analogs, including structural isomers, with different potency have been discovered in the field, there is a critical need to continue developing analytical methodologies capable of accurate identification in forensic and clinical laboratories. This study aimed to develop a rapid method for detecting and separating fentanyl isomers based on ion mobility-mass spectrometry (IM-MS), where IM separates gas-phase ions based on differences in their size, shape, and charge. Several strategies for improved differentiation were implemented, including using unconventional cation adducts (e.g., alkali and transition metals) and data post-processing by high-resolution demultiplexing. A collection of collision cross section (CCS) values for the various metal ion adducts was gathered, which can be used to improve confidence of identification in future samples. Notable examples, such as [M + Cu]+ and [M + Ag]+ adducts, contributed to significant improvement of resolution between isomers. Furthermore, the addition of high-resolution post-processing provided resolving power of >150, which constitutes a significant increase in comparison with the normal 50-60 obtained with low-resolution drift tube instruments. Collectively, these improved separation strategies allowed for confident detection and subsequent quantitative analysis. The optimized IM-MS method resulted in quantification of fentanyl in human urine with limits of detection and quantification of 13 pg/mL and 40 pg/mL, respectively.

OpenASAP: An affordable 3D printed atmospheric solids analysis probe (ASAP) mass spectrometry system for direct analysis of solid and liquid samples

Atmospheric Solids Analysis Probe (ASAP) mass spectrometry is a versatile technique allowing direct sampling of solid and liquid samples, but its adoption is limited due to the high cost of commercial ASAP systems. To address this, we present OpenASAP, an open-source ASAP system for mass spectrometers that can be fabricated for $20 or less using 3D-printing. Our design is readily adaptable to instruments from different manufacturers and can be produced with a variety of additive manufacturing techniques on consumer-grade 3D-printers. The probe allows for rapid sampling of solid and liquid samples without sample preparation, making it useful for high throughput screening, investigating spatial localization and function of analytes in biological samples, and incorporating mass spectrometry in instructional settings. We demonstrate its effectiveness by obtaining mass spectra of three natural product standards at levels as low as 10 ng/ml in liquid samples, and detecting these metabolites in microbial cultures that are difficult to analyze due to complex sample matrices or analyte properties. Furthermore, we demonstrate direct sampling of thin layer chromatography (TLC) spots of these cultures.

An economical setup for atmospheric pressure chemical ionization drift tube ion-mobility mass spectrometry

Ion-mobility (IM) separations-performed in conjunction with mass spectrometry (MS)-increase selectivity of MS analyses. However, IM-MS instruments are costly, and many laboratories are only equipped with standard MS instruments without an IM separation stage. Therefore, it is appealing to upgrade the existing mass spectrometers with low-cost IM separation devices. Such devices can be constructed using widely available materials such as printed-circuit boards (PCBs). We demonstrate coupling of an economical PCB-based IM spectrometer (disclosed previously) with a commercial triple quadrupole (QQQ) mass spectrometer. The presented PCB-IM-QQQ-MS system incorporates an atmospheric pressure chemical ionization (APCI) source, drift tube comprising desolvation and drift regions, ion gates, and transfer line to the mass spectrometer. The ion gating is accomplished with the aid of two floated pulsers. The separated ions are divided into packets, which are sequentially introduced to the mass spectrometer. Volatile organic compounds (VOCs) are transferred with the aid of nitrogen gas flow from the sample chamber to the APCI source. The operation of the system has been demonstrated using standard compounds. The limits of detection for 2,4-lutidine, (-)-nicotine, and pyridine are 2.02 × 10^-7 M, 1.54 × 10^-9 mol, and 4.79 × 10^-10 mol, respectively. The system was also used to monitor VOCs emitted from the porcine skin after exposure to nicotine patches, and VOCs released from meat undergoing the spoilage process. We believe this simple APCI-PCB-IM-QQQ-MS platform can be reproduced by others to augment the capabilities of the existing MS instrumentation.

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 (Rp^CCS) 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 Rp^CCS = 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.

A Comparison of the Performance of Modular Standalone Do-It-Yourself Ion Mobility Spectrometry Systems

As the spectrum of ion mobility spectrometry (IMS) applications expands and more experimental configurations are developed, identifying the correct platform for an experimental campaign becomes more challenging for researchers. Additionally, metrics that compare performance (Rp, for example) often have nuanced differences in definition between platforms that render direct comparisons difficult. Here we present a comparison of three do-it-yourself (DIY) drift tubes that are relatively low cost and easy to construct, where the performance of each is evaluated based on three different metrics: resolving power, the ideality of resolving powers, and accuracy/precision of K0 values. The standard PCBIMS design developed by Reinecke and Clowers (Reinecke, T.; Clowers, B. H. HardwareX 2018, 4, e00030) provided the highest resolving power (>90) and the highest ideality of resolving power ratios (>90% at best) of the three systems. However, the flexible tube (FlexIMS) construction as described by Smith et al. (Smith, B. L. Anal. Chem. 2020, 92 (13), 9104-9112) exhibited the highest degree of precision of K0 values (relative standard deviation of <0.42%). Depending on the application, the drift tube variants presented and evaluated here offer a low-cost alternative to commercial drift-tube systems with levels of performance that approach theoretical maxima.

Separation and Collision Cross Section Measurements of Protein Complexes Afforded by a Modular Drift Tube Coupled to an Orbitrap Mass Spectrometer

New developments in analytical technologies and biophysical methods have advanced the characterization of increasingly complex biomolecular assemblies using native mass spectrometry (MS). Ion mobility methods, in particular, have enabled a new dimension of structural information and analysis of proteins, allowing separation of conformations and providing size and shape insights based on collision cross sections (CCSs). Based on the concepts of absorption-mode Fourier transform (aFT) multiplexing ion mobility spectrometry (IMS), here, a modular drift tube design proves capable of separating native-like proteins up to 148 kDa with resolution up to 45. Coupled with high-resolution Orbitrap MS, binding of small ligands and cofactors can be resolved in the mass domain and correlated to changes in structural heterogeneity observed in the ion-neutral CCS distributions. We also demonstrate the ability to rapidly determine accurate CCSs for proteins with 1-min aFT-IMS-MS sweeps without the need for calibrants or correction factors.

Enhancing Separation and Constriction of Ion Mobility Distributions in Drift Tubes at Atmospheric Pressure Using Varying Fields

A linearly decreasing electric field has been previously proven to be effective for diffusional correction of ions in a varying field drift tube (VFDT) system, leading to higher resolving powers compared to a conventional drift tube due to its capacity to narrow distributions midflight. However, the theoretical predictions in resolving power of the VFDT were much higher than what was observed experimentally. The reason behind this discrepancy has been identified as the difference between the theoretically calculated resolving power (spatial) and the experimental one (time). To match the high spatial resolving power experimentally, a secondary high voltage pulse (HVP) at a properly adjusted time is used to provide the ions with enough momentum to increase their drift velocity and hence their time-resolving power. A series of systematic numerical simulations and experimental tests have been designed to corroborate our theoretical findings. The HVP-VFDT atmospheric pressure portable system improves the resolving power from the maximum expected of 60-80 for a regular drift tube to 250 in just 21 cm in length and 7kV, an unprecedent accomplishment.

Build, Share and Remix: 3D Printing for Speeding Up the Innovation Cycles in Ambient Ionisation Mass Spectrometry (AIMS)

Ambient ionisation mass spectrometry (AIMS) enables studying biological systems in their native state and direct high-throughput analyses. The ionisation occurs in the physical conditions of the surrounding environment. Simple spray or plasma-based AIMS devices allow the desorption and ionisation of molecules from solid, liquid and gaseous samples. 3D printing helps to implement new ideas and concepts in AIMS quickly. Here, we present examples of 3D printed AIMS sources and devices for ion transfer and manipulation. Further, we show the use of 3D printer parts for building custom AIMS sampling robots and imaging systems. Using 3D printing technology allows upgrading existing mass spectrometers with relatively low cost and effort.

Moving toward a Handheld "Plasma" Spectrometer for Elemental Analysis, Putting the Power of the Atom (Ion) in the Palm of Your Hand

Many of the current innovations in instrument design have been focused on making them smaller, more rugged, and eventually field transportable. The ultimate application is obvious, carrying the instrument to the field for real time sample analysis without the need for a support laboratory. Real time data are priceless when screening either biological or environmental samples, as mitigation strategies can be initiated immediately upon the discovery that contaminant metals are present in a location they were not intended to be. Additionally, smaller "handheld" instruments generally require less sample for analysis, possibly increasing sensitivity, another advantage to instrument miniaturization. While many other instruments can be made smaller just by using available micro-technologies (e.g., eNose), shrinking an ICP-MS or AES to something someone might carry in a backpack or pocket is now closer to reality than in the past, and can be traced to its origins based on a component-by-component evaluation. While the optical and mass spectrometers continue to shrink in size, the ion/excitation source remains a challenge as a tradeoff exists between excitation capabilities and the power requirements for the plasma's generation. Other supporting elements have only recently become small enough for transport. A systematic review of both where the plasma spectrometer started and the evolution of technologies currently available may provide the roadmap necessary to miniaturize the spectrometer. We identify criteria on a component-by-component basis that need to be addressed in designing a miniaturized device and recognize components (e.g., source) that probably require further optimization. For example, the excitation/ionization source must be energetic enough to take a metal from a solid state to its ionic state. Previously, a plasma required a radio frequency generator or high-power DC source, but excitation can now be accomplished with non-thermal (cold) plasma sources. Sample introduction, for solids, liquids, and gasses, presents challenges for all sources in a field instrument. Next, the interface between source and a mass detector usually requires pressure reduction techniques to get an ion from plasma to the spectrometer. Currently, plasma mass spectrometers are field ready but not necessarily handheld. Optical emission spectrometers are already capable of getting photons to the detector but could eventually be connected to your phone. Inert plasma gas generation is close to field ready if nitrogen generators can be miniaturized. Many of these components are already commercially available or at least have been reported in the literature. Comparisons to other "handheld" elemental analysis devices that employ XRF, LIBS, and electrochemical methods (and their limitations) demonstrate that a "cold" plasma-based spectrometer can be more than competitive. Migrating the cold plasma from an emission only source to a mass spectrometer source, would allow both analyte identification and potentially source apportionment through isotopic fingerprinting, and may be the last major hurdle to overcome. Finally, we offer a possible design to aid in making the cold plasma source more applicable to a field deployment.

Atmospheric Pressure Drift Tube Ion Mobility Spectrometry Coupled with Two-Dimensional Tandem Mass Spectrometry

Atmospheric pressure drift tube ion mobility was coupled with two-dimensional tandem mass spectrometry (2D MS/MS) in a linear ion trap to simultaneously collect ion mobility and the entire MS/MS data domain. Utilizing ion intensities from precursor ion and neutral loss scan lines, ion mobility spectra of multiple compounds with particular functional groups were acquired in a single experiment. Functional group-specific ion mobility spectra were demonstrated for a standard mixture of lipids. Additionally, ion mobility was used to separate isobaric ions prior to 2D MS/MS. The combination of these two methods offers improvements for the analysis of complex mixtures.

One-Dimensional Nanomaterials in Resistive Gas Sensor: From Material Design to Application

With a series of widespread applications, resistive gas sensors are considered to be promising candidates for gas detection, benefiting from their small size, ease-of-fabrication, low power consumption and outstanding maintenance properties. One-dimensional (1-D) nanomaterials, which have large specific surface areas, abundant exposed active sites and high length-to-diameter ratios, enable fast charge transfers and gas-sensitive reactions. They can also significantly enhance the sensitivity and response speed of resistive gas sensors. The features and sensing mechanism of current resistive gas sensors and the potential advantages of 1-D nanomaterials in resistive gas sensors are firstly reviewed. This review systematically summarizes the design and optimization strategies of 1-D nanomaterials for high-performance resistive gas sensors, including doping, heterostructures and composites. Based on the monitoring requirements of various characteristic gases, the available applications of this type of gas sensors are also classified and reviewed in the three categories of environment, safety and health. The direction and priorities for the future development of resistive gas sensors are laid out.

3D-Printed Microfluidic Nanoelectrospray Ionization Source Based on Hydrodynamic Focusing

Nanoelectrospray ionization (nESI) mass spectrometry (MS) is an ideal detection method for microfluidic chips, and its performances depend on nESI emitters. However, the fabrication of monolithic nESI emitters in chips was difficult. Herein, we propose a three-dimensional (3D) printing method to develop a microfluidic nanoelectrospray ionization source (NIS), composed of a nESI emitter and other components. Firstly, the NIS was compatible with a 50 - 500 nL min^-1 nanoflows by imposing 3D hydrodynamic focusing to compensate for the total flow rate, achieving a 7.2% best relative standard deviation in the total ion current (TIC) profiles. Additionally, it was applied to probe thirteen organic chemicals, insulin, and lysozyme with adequate signal-to-noise ratios and an accuracy of m/z between 9.02 × 10^-1 and 1.48 × 10³ ppm. Finally, the NIS achieved comparable limits of detection compared with its commercial counterpart. Considering the standardized preparation of NIS, it would be a potential option to develop 3D-printed customized Chip-MS platforms.

Rapid, low-cost, and in-situ analysis of per- and polyfluoroalkyl substances in soils and sediments by ambient 3D-printed cone spray ionization mass spectrometry

A rapid method to empirically determine the presence of trace per- and polyfluoroalkyl substances (PFAS) in solid media, such as soils, sands, and sediments, without any sample preparation, through ambient ionization mass spectrometry (MS), is described. 3D-printed cone spray ionization (3D-PCSI) is an ambient ionization technique that employs a 3D-printed conductive plastic cone to perform both sampling and ionization. The 3D-PCSI sources are fabricated in the shape of a hollowed square pyramid to hold bulk matrices, and consist of rigid walls to aid in the uniformity and consistency of sampling and ionization. Solid samples are placed within the hollowed pyramid and a solvent is added to perform an in-situ extraction, followed by spray-based ionization when a voltage is applied. The low cost of 3D-printing, its reproducibility at scale, and lack of sample preparation, enables 3D-PCSI-MS to rapidly and efficiently screen for trace PFAS, in-situ, in bulk samples. Demonstrated here is the detection of trace PFAS that were doped into six different soil and sediment matrices, by 3D-PCSI-MS, to validate the universality of the method, irrespective of matrix composition. All PFAS were identified by their indicative MS³ spectra and ranged in detection limits from 100 ppt to 10 ppb depending on the compound and soil classification. Legacy aqueous film forming foams (AFFF) were analyzed in soil by 3D-PCSI-MS, as were soil samples collected around an AFFF testing facility. The sampling rate for 3D-PCSI-MS was less than 2 min per sample, demonstrating the applicability to high-throughput mapping of a contaminated area.

The emerging role of 3D-printing in ion mobility spectrometry and mass spectrometry

3D-printing is revolutionizing the rapid prototyping in analytical chemistry. In the last few years, we observed the development of 3D-printed components for ion studies, such as ion sources, ion transfer and ion mobility spectrometry (IMS) devices. Often, 3D-printed gadgets add functions to existing mass spectrometry (MS) systems. Custom adapters improve the sensibility for coupling with ambient ionization and upstream chromatography methods, and sample preparation units optimize the following MS analyses. Besides, 3D-printer parts are suitable for constructing custom analytical robots and mass imaging systems. Some of those assemblies implement new concepts and are commercially not available. An essential aspect of using 3D-printing is the fast turnover of design improvements, which is motivated by permissive licenses. The easy reproducibility and exchange of ideas lead to a community-driven development, which is accompanied by economic advantages for public research and education.

Low-cost and open-source strategies for chemical separations

In recent years, a trend toward utilizing open access resources for laboratory research has begun. Open-source design strategies for scientific hardware rely upon the use of widely available parts, especially those that can be directly printed using additive manufacturing techniques and electronic components that can be connected to low-cost microcontrollers. Open-source software eliminates the need for expensive commercial licenses and provides the opportunity to design programs for specific needs. In this review, the impact of the "open-source movement" within the field of chemical separations is described, primarily through a comprehensive look at research in this area over the past five years. Topics that are covered include general laboratory equipment, sample preparation techniques, separations-based analysis, detection strategies, electronic system control, and software for data processing. Remaining hurdles and possible opportunities for further adoption of open-source approaches in the context of these separations-related topics are also discussed.

Flexible Drift Tube for High Resolution Ion Mobility Spectrometry (Flex-DT-IMS)

This paper describes, in detail, the development of a novel, low-cost, and flexible drift tube (DT) along with an associated ion mobility spectrometer system. The DT is constructed from a flexible printed circuit board (PCB), with a bespoke “dog-leg” track design, that can be rolled up for ease of assembly. This approach incorporates a shielding layer, as part of the flexible PCB design, and represents the minimum dimensional footprint conceivable for a DT. The low thermal mass of the polyimide substrate and overlapping electrodes, as afforded by the dog-leg design, allow for efficient heat management and high field linearity within the tube–achieved from a single PCB. This is further enhanced by a novel double-glazing configuration which provides a simple and effective means for gas management, minimizing thermal variation within the assembly. Herein, we provide a full experimental characterization of the flexible DT ion mobility spectrometer (Flex-DT-IMS) with corresponding electrodynamic (Simion 8.1) and fluid dynamic (SolidWorks) simulations. The Flex-DT-IMS is shown to have a resolution >80 and a detection limit of low nanograms for the analysis of common explosives (RDX, PETN, HMX, and TNT).

Analyzing Positive Reactant Ions in High Kinetic Energy Ion Mobility Spectrometry (HiKE-IMS) by HiKE-IMS-MS

In contrast to classical ion mobility spectrometers (IMS) operating at ambient pressure, the high kinetic energy ion mobility spectrometer (HiKE-IMS) is operated at reduced pressures between 10-40 mbar. In HiKE-IMS, ions are generated in a reaction region before they are separated in a drift region. Due to the operation at reduced pressure, it is possible to reach high reduced electric field strengths up to 120 Td in both the reaction as well as drift region, resulting in a pronounced decrease in chemical cross sensitivities and a significant enhancement of the dynamic range. Until now though, only limited knowledge about the ionization pathways in HiKE-IMS is available. Typically, proton bound water clusters, H⁺(H₂O)_n, are the most abundant positive reactant ion species in classical IMS with atmospheric chemical ionization sources. However, at reduced pressure and increased effective ion temperature, the reactant ion population significantly changes. As the ionization efficiency of analyte molecules in HiKE-IMS strongly depends on the reactant ion population, a detailed knowledge of the reactant ion population generated in HiKE-IMS is essential. Here, we present a coupling stage of the HiKE-IMS to a mass spectrometer enabling the identification of ion species and the investigation of ion molecule reactions prevailing in HiKE-IMS. In the present study, the HiKE-IMS-MS is used to identify positive reactant ion populations in both, purified air and nitrogen, respectively. The experimental data suggest the generation of systems of clustered primary ions (H⁺(H₂O)_n, NO⁺(H₂O)_m, and O₂⁺(H₂O)_p), which most probably serve as reactant ions. Their relative abundances highly depend on the reduced electric field strength in the reaction region. Furthermore, their effective mobilities are studied as a function of the reduced electric field strength in the drift region.

Identification and Confirmation of Fentanyls on Paper using Portable Surface Enhanced Raman Spectroscopy and Paper Spray Ionization Mass Spectrometry

Fentanyl and its analogues play a major role in the current opioid epidemic. In particular, these highly potent opioids have become a health hazard due to their use as additives in street drugs. Consequently, rapid on-site procedures for the analysis of this class of seized drugs are needed, especially considering the reported backlog of drug samples, which must undergo identification and confirmation tests to validate the presence of an illicit substance. Paper based devices are cheap sampling and analysis vehicles that have been shown capable of allowing rapid identification and confirmation of drugs of abuse. Modifying paper substrates by imprinting nanoparticles enables surface enhanced Raman spectroscopy (SERS) as well as a second analysis from the same substrate, namely paper spray ionization mass spectrometry. While such a procedure has been described for laboratory use, these illicit drug samples are typically collected in the field and this is where testing should be done. We combine paper SERS and paper spray MS on field-portable and commercial off-the-shelf (COTS) devices for the rapid and low-cost identification and confirmation of fentanyl and its analogues, enabling in situ analysis at the point of seizure of suspect samples. The commercial nature of both instruments moves this technology from the academic realm to a setting where the criminal justice system can realistically utilize it. The capabilities of this single-substrate dual-analyzer technique are further examined by sampling a variety of surfaces of forensic interest.

Pulsed Nano-ESI: Application in Ion Mobility-MS and Insights into Spray Dynamics

We have previously shown that pulsed nano-ESI offers direct ion introduction into an AP-IM cell in the absence of conventional gates and desolvation. Here, we further characterize this ion injection method and utilize it to gain insights into nano-ESI pulsed spray dynamics. We demonstrate that a pulsed nano-ESI operated at 20 Hz with ion generation pulses of 170-510 μs offers reproducible ion arrival times (0.09-0.21% RSD). Arrival times are then translated to effective collision cross sections (CCSs) using tetraalkylammonium ions as CCS internal standards. For ions with low solvent affinity, effective CCS values match those reported for fully desolvated ions. For amino acids and a series of alkylamine homologues, the effective CCS values are higher than those for fully desolvated ions and correlate with solvent affinity, suggesting that ions with high hydration affinities traverse the mobility cell as hydrated ions. Notably, hydrates are not observed in the MS spectra due to ion activation during the transport into vacuum. Using these observations as a framework to interpret effective CCS values, we investigate the impact of nano-ESI pulse duration on ion properties. We observe that longer pulse durations lead to the enhancement of ion abundance for low-ionization-efficiency analytes and a reduction in clustering. However, effective CCSs are not significantly altered by spray pulse duration, implying that similar ion structures emerge rapidly at all investigated pulse durations. Ion abundance results suggest a temporal evolution of droplets in pulsed nano-ESI where droplets emitted later in the spray formation appear to be smaller, providing enhanced ionization.