Experimental Evaluation of Higher Order Stability Zones Using a Digitally Operated Quadrupole Mass Filter.

Recent improvements to the comparison-based method of digital waveform generation increased the reproducibility of the waveforms so that the higher-order Mathieu stability zones can be accessed reliably. Digitally driven quadrupole mass filters access these zones using a fixed AC voltage and rectangular waveforms that are defined by a duty cycle. In this context, the duty cycle is the fraction of the waveform period where the waveform remains in the high state. Because digitally driven quadrupoles navigate stability using a duty cycle, there is no need to apply a resolving DC offset between electrode pairs. Accessing the higher stability zones using a conventional resonantly tuned RF requires the use of thousands of AC and DC voltages making the mode of operation less accessible with these devices. Stability zones higher than (1,1) and (2,1) have theoretical resolving powers that are on the order 1,140 and 3,447 at fwhm which drives efforts to practically access these operational conditions. Accessing these zones digitally requires the use of extremely precise waveforms. In a previous effort, waveform generation produced waveforms to reliably access the (1,1) and (2,1) zones without impacting performance. However, recent work found more improvement was needed to reliably access neighboring higher stability zones. Derived from that work, it was determined that a waveform resolution of ∼10 ppm or less was needed to reliably access the (3,1) and (3,2) zones. The present work utilized digital waveforms that achieve this level of precision to experimentally access and characterize attributes of the (3,1) and (3,2) zones. This work dives into the investigation of different beam energies to overcome the destabilizing fringing fields, improve transmission, and their overall effect on the experimental resolving power and signal-to-noise. In addition, the AC voltage of the driving RF was varied to understand the effects on the initial ion beam energy that is needed to achieve balanced separation and how the overall signal-to-noise is affected. Lastly, an assessment was made on the effects of the temporal parameters of a digital mass scan on peak sensitivity, peak fidelity, and overall duration for a scan.

A Modular Variable Temperature FT-IMS Instrument Optimized for Gas-Phase Ion Chemistry Applications.

The latest iteration of modular, open-source rolled ion mobility spectrometers was characterized and tailored for heated ion chemistry experiments. Because the nature of ion-neutral interactions is innately linked to the temperature of the drift cell, heated IMS experiments explicitly probe the fundamental characteristics of these collisions. While classic mobility experiments examine ions through inert buffer gases, doping the drift cell with reactive vapor enables desolvated chemical reactions to be studied. By using materials with minimal outgassing and ensuring the isolation of the drift tube from the surrounding ambient conditions, an open-source drift cell outfitted with heating components enables investigations of chemical reactions as a function of temperature. We show here that elevated temperatures facilitate an increase in deuterium incorporation and allow for hydrogen/deuterium exchanges otherwise unattainable under ambient conditions. While the initial fast exchanges get faster as temperature is increased, the slow rate which rises from the kinetic nonlinearity though to be attributed to ion-neutral clustering, remains constant with no change in mobility shifts. Additionally, we show the analytical merit of multiplexing mobility data by comparing the performance of traditional signal-averaging and FT-IMS modes.

Altering Conformational States of Dynamic Ion Populations using Traveling Wave Structures for Lossless Ion Manipulations.

With its capacity to store and translate ions across considerable distances and times, traveling wave structures for lossless ion manipulations (TW-SLIM) provide the foundation to expand the scope of ion mobility spectrometry (IMS) experiments. While promising, the dynamic electric fields and consequential ion-neutral collisions used to realize extensive degrees of separation have a considerable impact on the empirical results and the fundamental interpretation of observed arrival time distributions. Using a custom-designed set of TW-SLIM boards (∼9 m) coupled with a time-of-flight mass spectrometer (SLIM-ToF), we detail the capacity to systematically alter the gas-phase distribution of select peptide conformers. In addition to discussing the role charge-transfer may play in TW-SLIM experiments that occur at extended time scales, the ability of the SLIM-ToF to perform tandem IMS was leveraged to confirm that both the compact and elongated conformers of bradykinin2+ undergo interconversion within the SLIM. Storage experiments in which ions are confined within SLIM using static potential wells suggest that factors aside from TW-induced ion motion contribute to interconversion. Further investigation into this matter suggests that the use of radio frequency (RF) fields to confine ions within SLIM may play a role in ion heating. Aside from interconversion, storage experiments also provide insight into charge transfer behavior over the course of extended periods. The results of the presented experiments suggest that considerations should be taken when analyzing labile species and inform strategies for the TW-SLIM design and method development.

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%.

Nonlinear Frequency Modulation for Fourier Transform Ion Mobility Mass Spectrometry Improves Experimental Efficiency.

Through optimization of terminal frequencies and effective sampling rates, we have developed nonlinear sawtooth-shaped frequency sweeps for efficient Fourier transform ion mobility mass spectrometry (FT-IM-MS) experiments. This is in contrast to conventional FT-IM-MS experiments where ion gates are modulated according to a linear frequency sweep. Linear frequency sweeps are effective but can be hindered by the amount of useful signal obtained using a single sweep over a large frequency range imposed by ion gating inefficiencies, particularly small ion packets, and gate depletion. These negative factors are direct consequences of the inherently low gate pulse widths of high-frequency ion gating events, placing an upper bound on FT-IM-MS performance. Here, we report alternative ion modulation strategies. Sawtooth frequency sweeps may be constructed for the purpose of either extending high-SNR transients or conducting efficient signal-averaging experiments for low-SNR transients. The data obtained using this approach show high-SNR signals for a set of low-mass tetraalkylammonium salts (<1000 m/z) where resolving powers in excess of 500 are achieved. Data for low-SNR obtained for multimeric protein complexes streptavidin (53 kDa) and GroEL (800 kDa) also reveal large increases in the signal-to-noise ratio for reconstructed arrival time distributions.

Evaluation of Hydrogen-Deuterium Exchange during Transient Vapor Binding of MeOD with Model Peptide Systems Angiotensin II and Bradykinin.

The advancement of hybrid mass spectrometric tools as an indirect probe of molecular structure and dynamics relies heavily upon a clear understanding between gas-phase ion reactivity and ion structural characteristics. This work provides new insights into gas-phase ion-neutral reactions of the model peptides (i.e., angiotensin II and bradykinin) on a per-residue basis by integrating hydrogen/deuterium exchange, ion mobility, tandem mass spectrometry, selective vapor binding, and molecular dynamics simulations. By comparing fragmentation patterns with simulated probabilities of vapor uptake, a clear link between gas-phase hydrogen/deuterium exchange and the probabilities of localized vapor association is established. The observed molecular dynamics trends related to the sites and duration of vapor binding track closely with experimental observation. Additionally, the influence of additional charges and structural characteristics on exchange kinetics and ion-neutral cluster formation is examined. These data provide a foundation for the analysis of solvation dynamics of larger, native-like conformations of proteins in the gas phase.

SLIM Tricks: Tools, Concepts, and Strategies for the Development of Planar Ion Guides.

Traveling wave ion mobility experiments using planar electrode structures (e.g., structures for lossless ion manipulation, TW-SLIM) leverage the mature manufacturing capabilities of printed circuit boards (PCBs). With routine levels of mechanical precision below 150 µm, the conceptual flexibility afforded by PCBs for use as planar ion guides is expansive. To date, the design and construction of TW-SLIM platforms require considerable legacy expertise, especially with respect to simulation and circuit layout strategies. To lower the barrier of TW-SLIM implementation, we introduce Python-based interactive tools that assist in graphical layout of the core electrode footprints for planar ion guides with minimal user inputs. These scripts also export the exact component locations and assignments for direct integration into KiCad and SIMION for PCB finalization and ion flight simulations. The design concepts embodied in the set of scripts comprising SLIM Pickins (PCB CAD generation) and pigsim (SIMION workspace generation) build upon the lessons learned in the independent development of the research-grade TW-SLIM platforms in operation at WSU. Due to the inherent flexibility of the PCB manufacturing process and the time devoted to board layouts prior to manufacturing, both scripts serve to enable rapid, iterative design considerations. Because only a few predefined parameters are necessary (i.e., the TW-SLIM monomer width, x position following a TW Turn, and y position following a TW Turn) it is possible to design the exact component layouts and accompanying simulation space in a manner of minutes. There is no known limitation to the board layout capacities of the scripts, and the size of a designed layout is ultimately constrained by the abilities of the final PCB design and simulation tools, KiCad and SIMION, to accommodate the thousands of electrodes comprising the final design (i.e., RAM and software overhead). Toward removing the barriers to exploring new SLIM tracks and the likelihood of layout errors that require considerable revision and engineering time, the SLIM Pickins and pigsim tools (included as Supporting Information) allow the user to quickly design a length of planar ion guide, simulate its abilities to confine and transmit ions, compare hypothetical board outlines to given vacuum chamber dimensions, and generate a near-production ready PCB CAD file. In addition to these tools, this report outlines a series of cost-saving strategies with respect to vacuum feedthroughs and vacuum chamber design for TW ion mobility experiments using planar ion guides.

Evaluating dynamic traveling wave profiles for the enhancement of separation and sensitivity in traveling wave structures for lossless ion manipulations.

The amenability of traveling wave ion mobility spectrometry (TWIMS) to extended separation pathlengths has prompted a recent surge of interest concerning the technique. While promising, the optimization of ion transmission, particularly when analyzing increasingly disparate species, remains an obstacle in TWIMS. To address this issue, we evaluated a suite of dynamic TW profiles using an original TW structures for lossless ion manipulations (TW-SLIM) platform developed at Washington State University. Inspired by the range of gradient elution profiles used in traditional chromatography, three distinct square TW profiles were evaluated: a static approach which represents a traditional waveform, a dual approach which consists of two distinct TW profiles within a given separation event; and a ramp approach which varies TW speed and amplitude at a fixed rate during separation. The three waveform profiles were evaluated in terms of their impact on separation (quantified as resolution) and sensitivity (quantified using signal-to-noise ratio (SNR), and ion abundance). Concerning separation, the highest resolution (R) was observed when operating with the static waveform (R = 7.92); however, the ramp waveform performed comparably (R = 7.70) under similar conditions. Regarding SNR, optimum waveform profiles were species dependent. Bradykinin2+ displayed the largest gains in SNR (36.6% increase) when ramping TW speed, while the gains were greatest (33.5% increase) for tetraoctylammonium when modulating TW amplitude with the static waveform. Lastly, significant (>10%) increases in the abundance of tetraoctylammonium ions were observed exclusively when utilizing a ramped waveform. The present set of experiments outline the results and challenges related to optimizing separations using alternative TW profiles and provides insight concerning TW-SLIM method development which may be tailored to enhance select analytical metrics.

Simultaneous Ion Swarm Profiling and Ion Mobility Measurement using Ion Cameras.

When operated as a standalone analytical device, traditional drift tube ion mobility spectrometry (IMS) experiments require high-speed, high-gain transimpedance amplifiers to record ion separations with sufficient resolution. Recent developments in the fabrication of charge-sensitive cameras (e.g., IonCCD) have provided key insights for ion beam profiling in mass spectrometry and even served as detectors for miniature magnetic sector instruments. Unfortunately, these platforms have comparatively slow integration times (multiple ms), which largely precludes their use for recording ion mobility spectra, where sampling rates into the 10s of kHz are generally required. As a result, experiments that simultaneously probe the longitudinal and transverse mobility of an injected species using an array detector have not been reported. To address this duty-cycle mismatch, a frequency encoding strategy is used to evaluate ion swarm characteristics, while directly capturing ion mobility information using the Fourier transform. This apparatus described allows the ion beam to be profiled over the full course of the experiment and establishes the foundation to examine axial and longitudinal drift velocities simultaneously.

Implementation of an Open-Source Multiplexing Ion Gate Control for High Kinetic Energy Ion Mobility Spectrometry (HiKE-IMS).

With ion mobility spectrometry increasingly used in mass spectrometry to enhance separation by increasing orthogonality, low ion throughput is a challenge for the drift-tube ion mobility experiment. The High Kinetic Energy Ion Mobility Spectrometer (HiKE-IMS) is no exception and routinely uses duty cycles of less than 0.1%. Multiplexing techniques such as Fourier transform and Hadamard transform represent two of the most common approaches used in the literature to improve ion throughput for the IMS experiment; these techniques promise increased duty cycles of up to 50% and an increased signal-to-noise ratio (SNR). With no instrument modifications required, we present the implementation of Hadamard Transform on the HiKE-IMS using a low cost, high-speed (600 MHz), open source microcontroller, a Teensy 4.1. Compared to signal average mode, 7- to 10-bit pseudorandom binary sequences resulted in increased analyte signal by over a factor of 3. However, the maximum SNR gain of 10 did not approach the theoretical 2n-1 gain largely due to capacitive coupling of the ion gate modulation with the Faraday plate used as a detector. Even when utilizing an inverse Hadamard technique, capacitive coupling was not completely eliminated. Regardless, the benefits of multiplexing IMS coupled to mass spectrometers are well documented throughout literature, and this first effort serves as a proof of concept for multiplexing HiKE-IMS. Finally, the highly flexible Teensy used in this effort can be used to multiplex other devices or can be used for Fourier transform instead of Hadamard transform.

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.

FTflow: An Open-Source Python GUI for FT-IM-MS Experiments.

As part of a larger effort to aid in seamless integration of Fourier-based multiplexed ion mobility with a range mass analyzers, we have developed an all-in-one graphical user interface tool for FT-IM-MS data analysis that runs directly within a web browser. This tool, FTflow, accepts mzML files and displays necessary information such as mass spectra and extracted ion chromatograms in order to reconstruct arrival time distributions. It also extracts the corresponding mobility-related information (e.g., Ko and CCS) for each of the target ion populations. Furthermore, input fields for experimental conditions are clearly laid out for users and ease-of-use. With flexibility in mind, the processing scripts and GUI interface are written entirely in Python and allows users the option to modify source code to fit their specific needs. While the intention for this tool is to be a starting point for exploratory analysis of FT-IM-MS data, it has the capability to be adapted for use in more automated data processing pipelines through direct access of core processing routines.

Ion-neutral clustering alters gas-phase hydrogen-deuterium exchange rates.

The rates and mechanisms of chemical reactions that occur at a phase boundary often differ considerably from chemical behavior in bulk solution, but remain difficult to quantify. Ion-neutral interactions are one such class of chemical reactions whose behavior during the nascent stages of solvation differs from bulk solution while occupying critical roles in aerosol formation, atmospheric chemistry, and gas-phase ion separations. Through a gas-phase ion separation technique utilizing a counter-current flow of deuterated vapor, we quantify the degree of hydrogen-deuterium exchange (HDX) and ion-neutral clustering on a series of model chemical systems (i.e. amino acids). By simultaneously quantifying the degree of vapor association and HDX, the effects of cluster formation on reaction kinetics are realized. These results imply that cluster formation cannot be ignored when modeling complex nucleation processes and biopolymer structural dynamics.

Low-cost Arduino controlled dual-polarity high voltage power supply.

Ion Mobility Spectrometry (IMS) provides low ppbv detection limits for gas-phase or aqueous analytes. These instruments rely an electric field to produce ion motion. This electric field is typically 200-600 V/cm with a 15 cm cell, requiring an HV source of 6-10 kV. In this work, we present a low-cost alternative for supplying this high voltage. Inexpensive, commercially available 0-20 kV HV modules are mapped to an analog 0-5 V input signal, controlled using an Arduino microcontroller and digital analog converter. Dual polarities are selectable through a front-panel switch and ramps potentials between settings to avoid damage to attached devices.

Improving Ion Mobility Mass Spectrometry of Proteins through Tristate Gating and Optimization of Multiplexing Parameters.

Coupling drift tube ion mobility (IM) to Fourier transform mass spectrometry (FT-MS) affords the opportunity for gas-phase separation of ions based on size and conformation with high-resolution mass analysis. However, combining IM and FT-MS is challenging because ions exit the drift tube on a much faster time scale than the rate of mass analysis. Fourier transform (FT) and Hadamard transform multiplexing methods have been implemented to overcome the duty-cycle mismatch, offering new avenues for obtaining high-resolution, high-mass-accuracy analysis of mobility-selected ions. The gating methods used to integrate the drift tube with the FT mass analyzer discriminate against the transmission of large, low-mobility ions owing to the well-known gate depletion effect. Tristate gating strategies have been shown to increase ion transmission for drift tube IM-FT-MS systems through implementation of dual ion gating, controlling the quantity and timing of ions through the drift tube to reduce losses of slow-moving ions. Here we present an optimized set of multiplexing parameters for tristate gating ion mobility of several proteins on an Orbitrap mass spectrometer and further report parameters for increased ion transmission and mobility resolution as well as decreased experimental times from 15 min down to 30 s. On average, peak intensities in the arrival time distributions (ATDs) for ubiquitin increased 2.1× on average, while those of myoglobin increased by 1.5× with a resolving power increase on average of 11%.

Considerations for Generating Frequency Modulation Waveforms for Fourier Transform-Ion Mobility Experiments.

By casting the information regarding an ion population's mobility in the frequency domain, the coupling of time-dispersive ion mobility techniques is now imminently compatible with slower mass analyzers such as ion traps. Recent reports have detailed the continued progress toward maximizing the efficiency of the Fourier transform ion mobility-mass spectrometry (FT-IM-MS) experiments, but few reports have outlined the intersection between the practical considerations of implementation against the theoretical limits imposed by traditional signal processing techniques. One of the important concerns for Fourier-based multiplexing experiments is avoiding signal aliasing as a product of undersampled signals that may occur during data acquisition. In addition to traditional considerations such as detector sampling frequency, the limitations (i.e., maximum measurable drift time) imposed by experimental mass scan duration and the frequency sweep used for ion gate modulation must also be assessed. This work aims to connect the fundamental underpinnings of FT-IM-MS experiments and the associated experimental parameters that are encountered when coupling the comparatively fast separations in the mobility domain with the slower m/z scanning common for ion-trap mass analyzers. In addition to stating the relevant theory that applies to the FT-IM-MS experiment, this report highlights how aliased signals will manifest post Fourier transform in reconstructed arrival time distributions and calculated mobilities.

Characterization of a Modulated X-ray Source for Ion Mobility Spectrometry.

As a highly deployed field instrument for the detection of narcotics, explosives, and chemical warfare agents, drift tube ion mobility spectrometry relies heavily upon the performance of the ionization source and mechanism of ion beam modulation. For this instrumental platform, ion chemistry plays a critical role in the performance of the instrument from a sensitivity and selectivity perspective; however, a range of instrumental components also occupy pivotal roles. Most notably, the mechanism of ion modulation or ion gating is a primary contributor to peak width in a drift tube ion mobility experiment. Unfortunately, physical ion gates rarely perform perfectly, and in addition to serving as physical impediments to ion transmission, their modulation also has undesirable field effects. Using a recently developed modulated, non-radioactive X-ray source, we detail the performance of an ion mobility spectrometry (IMS) system that is free of a gating structure and utilizes the pulsed nature of the modulated X-ray source (MXS) for both ion generation and initiation of the IMS experiment. After investigating the influence of pulse duration and spatial X-ray beam width on the analytical performance of the instrument, the possibility of using multiplexing with a shutterless system is explored. By increasing ion throughput, the observed multiplexing gain compared to a signal-averaged spectrum approaches the theoretical maximum and illustrates the capability of the MXS-IMS system to realize significant signal to noise improvements.

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.

Condensable Vapor Sorption by Low Charge State Protein Ions.

Measurement of the gas-phase ion mobility of proteins provides a means to quantitatively assess the relative sizes of charged proteins. However, protein ion mobility measurements are typically singular values. Here, we apply tandem mobility analysis to low charge state protein ions (+1 and +2 ions) introduced into the gas phase by nanodroplet nebulization. We first determine protein ion mobilities in dry air and subsequently examine shifts in mobilities brought about by the clustering of vapor molecules. Tandem mobility analysis yields mobility-vapor concentration curves for each protein ion, expanding the information obtained from mobility analysis. This experimental procedure and analysis is extended to bovine serum albumin, transferrin, immunoglobulin G, and apoferritin with water, 1-butanol, and nonane. All protein ions appear to adsorb vapor molecules, with mobility "diameter" shifts of up to 6-7% at conditions just below vapor saturation. We parametrize results using κ-Köhler theory, where the term κ quantifies the extent of uptake beyond Köhler model expectations. For 1-butanol and nonane, κ decreases with increasing protein ion size, while it increases with increasing protein ion size for water. For the systems probed, the extent of mobility shift for the organic vapors is unaffected by the nebulized solution pH, while shifts with water are sensitive to pH.

Accelerating prototyping experiments for traveling wave structures for lossless ion manipulations.

Traveling wave structures for lossless ion manipulation (TW-SLIM) has proven a valuable tool for the separation and study of gas-phase ions. Unfortunately, many of the traditional components of TW-SLIM experiments manifest practical and financial barriers to the technique's broad implementation. To this end, a series of technological innovations and methodologies are presented which enable for simplified SLIM experimentation and more rapid TW-SLIM prototyping. In addition to the use of multiple independent board sets that comprise the present SLIM system, we introduce a low-cost, multifunctional traveling wave generator to produce TW within the TW-SLIM. This square-wave producing unit proved effective in realizing TW-SLIM separations compared to traditional approaches. Maintaining a focus on lowering barriers to implementation, the present set of experiments explores the use of on-board injection (OBI) methods, which offer potential alternatives to ion funnel traps. These OBI techniques proved feasible and the ability of this simplified TW-SLIM platform to enhance ion accumulation was established. Further experimentation regarding ion accumulation revealed a complexity to ion accumulation within TW-SLIM that has yet to be expounded upon. Lastly, the ability of the presented TW-SLIM platform to store ions for extended periods (1 s) without significant loss (<10%) was demonstrated. The aforementioned experiments clearly establish the efficacy of a simplified TW-SLIM platform which promises to expand adoption and experimentation of the technique.