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

Instrumental developments in drift tube ion mobility spectrometry: A review on miniaturization, new manufacturing techniques, and pre-separation

Drift tube ion mobility spectrometry (DT-IMS) separates ions based on their mobility under weak electric fields and has undergone significant advancements since its introduction as an analytical instrument in 1970. Recent developments in DT-IMS focus on addressing limitations such as low resolving power and challenges in separating complex samples. High-resolution ion shutters, optimized drift tubes, and integrated chip-based pre-separation methods have greatly enhanced analytical performance. Miniaturization has been a key focus, driven by advanced manufacturing techniques and instrumental developments, which have improved portability, reduced costs, and enabled custom designs. Tandem DT-IMS systems further enhance selectivity and structural elucidation, offering expanded capabilities for complex analyses. These innovations have significantly advanced the functionality of DT-IMS, bridging the gap between simple, straightforward designs and high analytical performance. This review highlights the transformative impact of these instrumental developments, miniaturization, and novel manufacturing techniques, positioning DT-IMS as a versatile, high-performance analytical tool for modern workflows.

High resolving power electrospray drift tube ion mobility spectrometer with heated desolvation tube

BACKGROUND

The separation performance of drift tube ion mobility spectrometers is usually relatively weak with resolving powers well below 100. Improving this aspect requires, besides the optimization of other parameters, the challenging increase of the drift voltage as deduced from fundamental equations describing the broadening of a drifting ion swarm. We recently succeeded in constructing an improved high voltage instrument equipped with an electrospray source capable of analysing liquid samples with resolving powers above 200. This instrument was further perfected with a newly developed heated desolvation tube guiding the ions to the injection gate. The electrospray desolvation process was thus enhanced while the separation region was maintained at room temperature to keep diffusional band broadening to a minimum. A further modification was also made to the detector circuitry in order to reduce its noise.

RESULTS

To demonstrate the performance of the instrument several challenging ion mixtures, including two herbicides, a polymer mixture, and isomers of carnitine esters were successfully separated and detected. The resolving powers, calculated from the arrival time and peak width at half height, ranged from 123 to 228. The latter value represents 96 % of the theoretically achievable resolving power at the working drift voltage of 24.1 kV.

SIGNIFICANCE

Stand-alone electrospray ion mobility spectrometry is not often used and has not yet been developed to its full potential. The results with improved resolving powers demonstrate its capability as a simple technique for the analysis of liquid samples, which may often serve as a lower cost alternative to chromatography or mass spectrometry.

Ultrahigh Resolving Power Ion Mobility Spectrometry with a Simple Pulser Circuitry

The pulsing circuitry for high resolving power drift-tube ion-mobility spectrometry is based on three avalanche photodiodes. These are switched on by illumination through optical fibers, which provide electrical insulation of the driver circuitry from the high voltage. The setup was tested with a series of quaternary ammonium ions introduced with an electrospray ion source. Two instruments with drift tubes of 10 and 30 cm length were employed and a separation voltage of up to 23.7 kV. Resolving powers above 200 could be achieved for the longer tube, which are comparable to those obtained with a previously employed more elaborate electrically floating pulser. The new pulser allows the creation of common two-state injection pulses as well as tristate pulses known to reduce the discrimination of low mobility ions. A comparison between the two pulsing regimes showed that, as predicted by theory, for the longer tube, the discrimination of low-mobility ions in the two-state shutter mode was less significant than for the shorter tube.

High Resolution Ion Mobility Enables the Structural Characterization of Atropisomers of GDC-6036, a KRAS G12C Covalent Inhibitor

GDC-6036 is a covalent KRAS G12C inhibitor that demonstrates high potency and selectivity. Structurally, GDC-6036 consists of several motifs that make the analytical characterization of this molecule challenging, including a highly basic pyrrolidine motif bonded to a quinazoline ring via an ether bond and an atropisomeric carbon-carbon bond between functionalized pyridine and quinazoline groups. Structurally, the desired atropisomer was synthesized via an atroposelective Negishi coupling with very high yield. However, having a direct way to analyze and confirm the presence of the atropisomeric species remained challenging in routine analytical workflows. In this study, both variable temperature nuclear magnetic resonance (VT-NMR) and two different approaches of in-line ion mobility coupled to liquid chromatography mass spectrometry (LC-MS) workflows were evaluated for the characterization of GDC-6036 and its undesired atropisomer (Compound B) to support synthetic route development. Briefly, both VT-NMR and traveling wave ion mobility spectrometry (TWIMS) enabled by structures for lossless ion manipulation (SLIM) technology coupled to high resolution MS (HRMS) are able to elucidate the structures of the atropisomers in a complex mixture. Drift tube IMS (DTIMS) was also evaluated, but lacked the resolving power to demonstrate separation between the two species in a mixture, but did show slight differences in their arrival times when multiplexed and injected separately. The determined resolving power (Rp) by multiplexing the ions via DTIMS was 67.3 and 60.5 for GDC-6036 and Compound B, respectively, while the two peak resolving power (Rpp) was determined to be 0.41, indicating inadequate resolution between the two species. Alternatively, the SLIM-IM studies showed Rp of 103.8 and 99.4, with a Rpp of 2.64, indicating good separation between the atropisomers. Furthermore, the CCS/z for GDC-6036 and Compound B was determined to be 231.2 Å2/z and 235.0 Å2/z, respectively. Quantitative experiments demonstrate linearity (R2 >0.99) for both GDC-6036 and Compound B while maintaining separation via SLIM-IM. Spike recoveries of one atropisomer relative to the other yielded strong recoveries (98.7% to 102.5%) while maintaining reproducibility (<7% RSD). The study herein describes the analytical process for evaluating new technologies and strategies for implementation in routine biopharmaceutical characterization workflows.

High Resolving Power Electrospray Ionization Ion Mobility Spectrometer Based on Fourier Deconvolution Multiplexing

The resolving power of the drift tube ion mobility spectrometry (IMS) is mainly dependent on the drift length, the drift voltage, the pulse width of an ion gate, and the pressure inside the drift tube. Electrospray ionization (ESI)-IMS is a highly sensitive and reliable technique for the detection and analysis of nonvolatile compounds, and high resolving power is necessary to separate structurally similar compounds. To improve the analytical performance of atmospheric pressure ESI-IMS, the Fourier deconvolution (FD) multiplexing technique is investigated as an effective and convenient means to improve the resolving power as well as the signal-to-noise ratio. By reducing the equivalent ion gate opening width to 5 μs using a typical Tyndall-Powell ion shutter, a high resolving power RP up to 170 can be achieved with a drift length of 12 cm and a drift voltage of 10 kV. Rhodamine 6G (R6G), sodium dodecyl sulfate (SDS), methacycline, oxytetracycline, and ractopamine were evaluated using the FD-ESI-IMS, and mixtures with similar ion mobility can be well separated without prolonging the drift length.

A modular, isolated high-voltage switch for application in ion mobility spectrometry

Ion mobility spectrometry is an emerging technology in trace gas analysis that has moved from typical safety and security applications to many other fields ranging from environmental and food quality monitoring to medicine and life sciences. Nevertheless, further dissemination, including the development of new instruments and the expansion into new fields of application requires the availability of the fundamental components of ion mobility spectrometers. For example, the electronics is essential for the analytical performance, but is only provided by specialized manufacturers due to specific requirements. In this paper, we present a modular, isolated high-voltage switch that can be operated at an isolated potential. The modular design enables tailoring its configuration to the required application. Each module can switch a voltage of up to 3 kV, and can be operated with an offset voltage of up to 7 kV. The switch has rise and fall times of less than 25 ns, making it suitable for a wide range of applications, e.g., in ion mobility spectrometry. Finally, the presented modular, isolated high-voltage switch was used in a push-pull configuration to generate the injection pulse of the ion gate. The new modular, isolated high-voltage switch shows similar performance compared to a commercially available high-voltage switch.

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.

Setting the Separation Factor α for Ketone Monomers and Dimers by the Use of Different Drift Gases

This study investigates the influence of different drift gases on ion mobility in ion mobility spectrometry (IMS) using ketones as model substances within a custom-built drift tube spectrometer. Different binary mixtures of nitrogen, helium, and argon were used as drift gases to investigate the influence of mobility on the monomers and dimers of the different ketones. Experimental results reveal shifts in ion drift times and separation factors (α) with varying gas compositions, in accordance with Blanc's Law. Furthermore, the study underscores the device-independent nature of α and the device-dependent resolution, emphasizing the importance of comparative analyses. Employing 2-hexanone and 2-decanone in the same sample but with different drift gases is used to show the impact of different drift gases. By changing the drift gas composition, total alignment of drift times and therefore no possible resolution or baseline resolution could be achieved. Through different experiments and analyses, this research provides insights into the interactions between gas composition and ion mobility, offering implications for diverse analytical applications from environmental monitoring to chemical detection.

Advances of Ion Mobility Platform for Plant Metabolomics

Metabolomics aims to profile the extensive array of metabolites that exists in different types of matrices using modern analytical techniques. These techniques help to separate, identify, and quantify the plethora of chemical compounds at various analytical platforms. Hence, ion mobility spectrometry (IMS) has emerged as an advanced analytical approach, exclusively owing to the 3D separation of metabolites and their isomers. Furthermore, separated metabolites are identified based on their mass fragmentation pattern and CCS (collision cross-section) values. The IMS provides an advanced alternative dimension to separate the isomeric metabolites with enhanced throughput with lesser chemical noise. Thus, the present review highlights the types, factors affecting the resolution, and applications of IMMS (Ion mobility mass spectrometry) for isomeric separations, and ionic contaminants in the plant samples. Furthermore, an overview of IMS-based applications for the identification of plant metabolites (volatile and non-volatile) over the last few decades has been discussed, followed by future assumptions for creating IM-based databases. Such approaches could be significant to accelerate and improve our knowledge of the vast chemical diversity found in plants.

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 Fourier deconvolution ion mobility spectrometer as high-performance gas chromatography detector for the analysis of plant extract flavors

The Fourier deconvolution ion mobility spectrometer (FDIMS) offers multiplexing and improves the resolving power and signal-to-noise ratio. To evaluate the FDIMS as a detector for gas chromatography for the analysis of complex samples, we connected a drift tube ion mobility spectrometer to a commercial gas chromatograph and compared the performance including resolving power, sensitivity, and linear range using 2,6-di‑tert-butylpyridine. Mixed standards were also injected into the tandem system to evaluate the performance under optimized conditions. A complex plant extract sample used as natural flavoring was investigated using the resulting system. The results show that the instrument implemented with the Fourier deconvolution multiplexing method demonstrated higher performance over the traditional signal averaging method including higher resolving power, better limit of detection, and wider linear range for a variety of compounds and natural plant extract flavorings.

Room-temperature phosphorescence and fluorescence nanocomposites as a ratiometric chemosensor for high-contrast and selective detection of 2,4,6-trinitrotoluene

Reports on using complementary colours for high-contrast ratiometric assays are limited to date. In this work, graphitized carbon nitride (g-C3N4) nanosheets and mercaptoethylamine (MEA) capped Mn-doped ZnS QDs were fabricated by liquid exfoliation of bulk g-C3N4, and by a coprecipitation and postmodification strategies, respectively. Mn-doped ZnS quantum dots were deposited onto g-C3N4 nanosheets through an electrostatic self-assembly to form new nanocomposites (denoted as Mn-ZnS QDs@g-C3N4). Mn-ZnS QDs@g-C3N4 can emit a pair of complementary colour light, namely, orange room-temperature phosphorescence (RTP) at 582 nm and blue fluorescence at 450 nm. After 2,4,6-trinitrotoluene (TNT) dosing into Mn-ZnS QDs@g-C3N4 aqueous solution, and pairing with MEA to generate TNT anions capable of quenching the emission of Mn-doped ZnS QDs, the fluorescence colours of the solution changed from orange to blue across white, exhibiting unusual high-contrast fluorescence images. The developed ratiometric chemosensor showed very good linearity in the range of 0-12 μM TNT with a limit of detection of 0.56 μM and an RSD of 6.4 % (n = 5). Also, the ratiometric probe had an excellent selectivity for TNT over other nitroaromatic compounds, which was applied in the ratiometric test paper to image TNT in water, and TNT sensing under phosphorescence mode to efficiently avoid background interference. A high-contrast dual-emission platform for selective ratiometric detection of TNT was therefore established.

Analytical Tools and Methods for Explosive Analysis in Forensics: A Critical Review

This review summarizes (i) compositions and types of improvised explosive devices; (ii) the process of collection, extraction and analysis of explosive evidence encountered in explosive and related cases; (iii) inter-comparison of analytical techniques; (iv) the challenges and prospects of explosive detection technology. The highlights of this study include extensive information regarding the National & International standards specified by USEPA, ASTM, and so on, for explosives detection. The holistic development of analytical tools for explosive analysis ranging from conventional methods to advanced analytical tools is also covered in this article. The most important aspect of this review is to make forensic scientists familiar with the challenges during explosive analysis and the steps to avoid them. The problems during analysis can be analyte-based, that is, interferences due to matrix or added molding/stabilizing agents, trace amount of parent explosives in post-blast samples and many more. Others are techniques-based challenges viz. specificity, selectivity, and sensitivity of the technique. Thus, it has become a primary concern to adopt rapid, field deployable, and highly sensitive techniques.

Focusing ion funnel-assisted ambient electrospray enables high-density and uniform deposition of non-spherical gold nanoparticles for highly sensitive surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) is a powerful technique for detecting trace amounts of analytes. However, the performance of SERS substrates depends on many variables including the enhancement factor, morphology, consistency, and interaction with target analytes. In this study, we investigated, for the first time, the use of electrospray deposition (ESD) combined with a novel ambient focusing DC ion funnel to deposit a high density of gold nanoparticles (AuNPs) to generate large-area, uniform substrates for highly sensitive SERS analysis. We found that the combination of ambient ion focusing with ESD facilitated high-density and intact deposition of non-spherical NPs. This also allowed us to take advantage of a polydisperse colloidal solution of AuNPs (consisting of nanospheres and nanorods), as confirmed by finite-difference time domain (FDTD) simulations. Our SERS substrate exhibited excellent capture capacity for model analyte molecules, namely 4-aminothiophenol (4-ATP) and Rhodamine 6G (R6G), with detection limits in the region of 10-11 M and a relative standard deviation of <6% over a large area (∼500 × 500 μm2). Additionally, we assessed the quantitative performance of our SERS substrate using the R6G probe molecule. The results demonstrated excellent linearity (R2 > 0.99) over a wide concentration range (10-4 M to 10-10 M) with a detection limit of 80 pM.

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.

Electrospray Ion Mobility Spectrometer Based on Flexible Printed-Circuit Board Electrodes with Improved Resolving Power

An easily built drift tube instrument with ring electrodes made of rolled-up flexible printed circuit boards is reported. Its resolving power was maximized by careful attention to the drift tube geometry and the response time of the detector amplifier and by employing a high separation field strength. The separation of singly charged aliphatic quaternary ammonium ions introduced by electrospray was performed, and the measured resolving power was between 86 and 97% of the theoretical limit for three different drift tube lengths investigated. For the longest drift length of 30 cm, a resolving power of up to 228 was obtained. Three benzalkonium chlorides were also separated with resolving powers of over 210. The tristate injection scheme can also be used, with only a small loss of the separation performance compared to the two-state injection.

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.

Tuning solvent-solute interactions enable visual colorimetric detection of nitro-aromatic explosives

The Janowski reaction is a critical reaction for visual colorimetric detection of nitro-aromatic explosives. However, the solvent effect is still not well explored. Herein, we report the solvent-dependent activity of the Janowski reaction between 2,4-dinitrotoluene (DNT)/2,4,6-trinitrotoluene (TNT) and NaOH. Four common solvents are studied. It is found that acetone with high donor number and low polarity is able to readily dissolve the product of Janowski reaction (Meisenheimer complexes) via Lewis acid-base interactions and solvation rules, facilitating the Janowski reactions between DNT/TNT and NaOH. Based on the color change of the Janowski reactions within acetone, a visual colorimetric assay is established. The present assay can detect DNT and TNT with a detection limit of 1.4 μM and 1.2 μM, which allows for naked-eye detection. In addition, this assay is highly selective and applicable to DNT/TNT detection in soil samples. Our work reveals the solvent effect on the Janowski reaction, providing a simple and rapid method for detection of nitro-aromatic explosives.

High voltage pulser for ion shutters in ion mobility spectrometry based on an optocoupler

A novel high voltage pulser for an ion shutter used in drift-tube ion-mobility spectrometers is described. The simple design suitable for the in-house construction of these spectrometers relies on a special optocoupler to isolate the triggering circuitry from the high voltage at the ion shutter. The device was tested with an electrospray-ionization ion-mobility device with a 10 cm drift tube operated at 4 kV into which a standard test mixture of four tetraalkylamines was injected with a negative going gating pulse of about 50 V on top of 4 kV. A fall time of 15.7 µs and a rise time of 2.0 µs were determined for the pulse, which was adequate for the required injection pulse width of 450 µs. Resolving powers between 61 and 81 were determined for the four quaternary amines, which were found to be comparable to the performance obtained with a previously reported pulser circuitry of a different design used as a reference.

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.

Rapid geographical indication of peppercorn seeds using corona discharge mass spectrometry

With increasing demands for more rapid and practical analyses, various techniques of ambient ionization mass spectrometry have gained significant interest due to the speed of analysis and abundance of information provided. Herein, an ambient ionization technique that utilizes corona discharge was applied, for the first time, to analyze and categorize whole seeds of black and white peppers from different origins. This setup requires no solvent application nor gas flow, thus resulting in a very simple and rapid analysis that can be applied directly to the sample without any prior workup or preparation. Combined with robust data pre-processing and subsequent chemometric analyses, this analytical method was capable of indicating the geographical origin of each pepper source with up to 98% accuracies in all sub-studies. The simplicity and speed of this approach open up the exciting opportunity for onsite analysis without the need for a highly trained operator. Furthermore, this methodology can be applied to a variety of spices and herbs, whose geographical indication or similar intellectual properties are economically important, hence it is capable of creating tremendous impact in the food and agricultural industries.

Development of simple drift tube design for ion mobility spectrometry based on flexible printed circuit board material

A study on the use of flexible printed circuit board material for the construction of drift tubes for ion mobility spectrometry is reported. This is significantly less complicated than the conventional approach based on stacked electrode and insulator rings, as the material can simply be rolled up to obtain a string of circular electrodes. The size and spacing of the electrodes was found to have a strong effect on the resolving power. For an optimized geometry with electrodes of 1.5 mm width at a pitch of 3.5 mm resolving powers of up to 80 were achieved for quaternary amines introduced by electrospray ionization into a drift tube of 10 cm length and an applied voltage of 4200 V. This performance was found to be comparable to that of a conventional drift tube based on stacked rings with otherwise identical geometry and operating conditions. The entire instrument was constructed in-house. Its utility was demonstrated with the determination of the C12, C14 and C16 benzalkonium ions in several commercial cleaning products with limits of detection of 20, 25, and 38 μg L^-1, respectively.

Toward Compact High-Performance Ion Mobility Spectrometers: Ion Gating in Ion Mobility Spectrometry

Printed circuit board (PCB) based drift tube ion mobility spectrometers enable the use of state-of-the-art production techniques to manufacture compact devices with excellent performance at minimum cost. The new PCB ion mobility spectrometer (PCB-IMS) presented here is equipped with either a 140 MBq tritium or a 95 MBq nickel-63 ionization source and consists of a combination of horizontally arranged 6-layer PCBs for the drift and reaction regions and vertically arranged PCBs for interfacing the ionization source, ion shutter, and detector. The design allows the reproducible manufacturing and thus comparison of different IMS topologies. Here, we investigate different ion shutters, field-switching, Bradbury-Nielsen, and tristate and their effects on resolving power and limits of detection considering two different ionization region geometries and ionization sources, tritium and nickel-63. It is shown that the high resolving power of R_P > 80 at low drift voltage of 3 kV and short drift length of 50 mm can be achieved independent of the used ion shutter mechanism and reaction region geometry. While the resolving power of all ion shutters is excellent, the Bradbury-Nielsen shutter shows a pronounced discrimination of slow ion species when using short shutter opening times for small initial ion cloud widths, as required for high resolving power. Thus, the intensity of the proton-bound dimer of 2-pentanone is reduced by 30% compared to the signal intensity obtained with both the field-switching and tristate shutter. The detection limits employing the Bradbury-Nielsen shutter and a 50 mm reaction region as required for nickel-63 are 58 ppt_v for the protonated monomer and 3.4 ppb_v for the proton-bound dimer of 2-pentanone. The detection limits achieved with the tristate shutter utilizing the same reaction region are slightly higher for the protonated monomer at 68 ppt_v, but lower for the proton-bound dimer at 2 ppb_v due to the advanced ion shutter principle not discriminating slow ions. However, the lowest detection limits of 13 ppt_v and 301 ppt_v can be achieved with the field-switching shutter and a 2 mm reaction region, sufficient for a tritium ionization source.

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.

Accelerated nucleophilic substitution reactions of dansyl chloride with aniline under ambient conditions via dual-tip reactive paper spray

Paper spray ionization (PSI) mass spectrometry (MS) is an emerging tool for ambient reaction monitoring via microdroplet reaction acceleration. PSI-MS was used to accelerate and monitor the time course of the reaction of dansyl chloride with aniline, in acetonitrile, to produce dansyl aniline. Three distinct PSI arrangements were explored in this study representing alternative approaches for sample loading and interaction; conventional single tip as well as two novel setups, a dual-tip and a co-axial arrangement were designed so as to limit any on-paper interaction between reagents. The effect on product abundance was investigated using these different paper configurations as it relates to the time course and distance of microdroplet travel. It was observed that product yield increases at a given distance and then decreases thereafter for all PSI configurations. The fluorescent property of the product (dansyl aniline) was used to visually inspect the reaction progress on the paper substrate during the spraying process. Amongst the variety of sample loading methods the novel dual-tip arrangement showed an increased product yield and microdroplet density, whilst avoiding any on-paper interaction between the reagents.