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While the resolving power of drift tube ion mobility spectrometers has been studied and modelled in detail over the past decades, no comparable model exists for the signal-to-noise-ratio. In this work, we develop an analytical model for the signal-to-noise-ratio of a drift tube ion mobility spectrometer based on the same experimental parameters used for modelling the resolving power. The resulting holistic model agrees well with experimental results and allows simultaneously optimizing both resolving power and signal-to-noise-ratio. Especially, it reveals several unexpected relationships between experimental parameters. First, even though reduced initial ion packet widths result in fewer injected ions and reduced amplifier widths result in more noise, the resulting shift of the optimum operating point when reducing both simultaneously leads to a constant signal-to-noise-ratio. Second, there is no dependence of the signal-to-noise-ratio at the optimum operating point on the drift length, as again the resulting shift of the optimum operating point causes all effects to compensate each other.

Interactions between anions and synthetic macrocyclic receptors belong to the extensively explored area of research due to the particularly important functions of anions in biological and environmental sciences. Structures of anion-macrocycle complexes are closely related to their function, highlighting the importance of structural analysis of the complexes. Here, we discuss the application of ion mobility mass spectrometry (IM-MS) and theoretical calculations to the structural analysis of tetralactam macrocycles (M) with varying flexibility and structural properties, and their complexes with anions [M + X]−. Collision cross section (CCS) values obtained from both direct drift tube (DT) and indirect using traveling-wave (TW) IM-MS measurements supplemented by theoretical calculations were successfully used to describe the structural properties of various macrocycle-anion complexes, proving the suitability of the IM-MS approach for sensitive, selective, and fast detection of anion complexes and characterization of their structures and conformations.

Ion mobility spectrometers (IMS) are able to detect pptV-level concentrations of substances in gasses and in liquids within seconds. Due to the continuous increase in analytical performance and reduction of the instrument size, IMS are established nowadays in a variety of analytical field applications. In order to reduce the manufacturing effort and further enhance their widespread use, we have developed a simple manufacturing process for drift tubes based on a composite material. This composite material consists of alternating layers of metal sheets and insulator material, which are connected to each other in a mechanically stable and gastight manner. Furthermore, this approach allows the production of ion drift tubes in just a few steps from a single piece of material, thus reducing the manufacturing costs and efforts. Here, a drift tube ion mobility spectrometer based on such a composite material is presented. Although its outer dimensions are just 15 mm × 15 mm in cross section and 57 mm in length, it has high resolving power of Rp = 62 and detection limits in the pptV-range, demonstrated for ethanol and 1,2,3-trichloropropane.

Elucidating the structures and stabilities of proteins and their complexes is paramount to understanding their biological functions in cellular processes. Native mass spectrometry (MS) coupled with ion mobility spectrometry (IMS) is emerging as an important biophysical technique owing to its high sensitivity, rapid analysis time, and ability to interrogate sample complexity or heterogeneity and the ability to probe protein structure dynamics. Here, a commercial IMS-MS platform has been modified for static native ESI emitters and an extended mass-to-charge range (20 kDa m/z) and its performance capabilities and limits were explored for a range of protein and protein complexes. The results show new potential for this instrument platform for studies of large protein and protein complexes and provides a roadmap for extending the performance metrics for studies of even larger, more complex systems, namely, membrane protein complexes and their interactions with ligands.

Ion mobility spectrometry (IMS) is a widely used technique based on gas phase ion separation under an electric field by differences in ion mobilities. In the last decade, IMS techniques have received increased attention due to their high operational speed and sensitivity. Currently, there are different IMS devices focused on solving different analytical performances, mainly based on linear drift tube (DT IMS), traveling wave, and field asymmetric waveform ion mobility spectrometers. In this review we summarize the main applications of DT-IMS devices for the determination of semi-volatile hazardous chemicals such as: illegal drugs, pesticides, explosives, chemical warfare agents, and others, in different matrices, in order to provide a detailed view of the analytical features of the technique.

Ion mobility was integrated with liquid chromatography/high resolution mass spectrometry (LC/IM-HRMS) to quantify 25-hydroxyvitamin D (25OHD) in human serum. It has previously been shown that 25OHD adopts two gas-phase conformations which are resolved using ion mobility; in contrast, the inactive epimer, 3-epi-25-hydroxyvitamin D (epi25OHD) only adopts one. Interference from epi25OHD was eliminated by filtering the chromatogram to retain the drift time that corresponds to the unique gas-phase conformation of 25OHD. Although ion mobility separates the epimers, some chromatography is required to separate compounds which interfere with ionization or fall at the same nominal m/z. Standards were prepared in 4% albumin solutions and compared against commercial serum quality controls. Standards and quality controls were analyzed and validated using a two-minute LC/IM-MS method. 25-hydroxyvitamin D3 and D2 were quantified over the range between 2 and 500 ng/mL with bias and precision within 15%. When epi25OHD was spiked into quality control samples, no significant bias was introduced, and analysis of 30 patient samples shows good agreement between this LC/IM-MS and traditional LC/MS/MS methods. This work shows that ion mobility can be incorporated with liquid chromatography and mass spectrometry for rapid quantitation of 25OHD in human serum.

In a previous work, we explored zone broadening and the achievable plate numbers in linear drift tube ion mobility-mass spectrometry through developing a plate-height model [1]. On the basis of these findings, the present theoretical study extends the model by exploring peak-to-peak resolution and peak capacity in ion mobility separations. The first part provides a critical overview of chromatography-influenced resolution equations, including refinement of existing formulae. Furthermore, we present exact resolution equations for drift tube ion mobility spectrometry based on first principles. Upon implementing simple modifications, these exact formulae could be readily extended to traveling wave ion mobility separations and to cases when ion mobility spectrometry is coupled to mass spectrometry. The second part focuses on peak capacity. The well-known assumptions of constant plate number and constant peak width form the basis of existing approximate solutions. To overcome their limitations, an exact peak capacity equation is derived for drift tube ion mobility spectrometry. This exact solution is rooted in a suitable physical model of peak broadening, accounting for the finite injection pulse and subsequent diffusional spreading. By borrowing concepts from the theoretical toolbox of chromatography, we believe that the present study will help in integrating ion mobility spectrometry into the unified language of separation science.

Ion mobility (IM) is a gas phase separation strategy that can either supplement or serve as a high-throughput alternative to liquid chromatography (LC) in shotgun lipidomics. Incorporating the IM dimension in untargeted lipidomics workflows can help resolve isomeric lipids, and the collision cross section (CCS) values obtained from the IM measurements can provide an additional molecular descriptor to increase lipid identification confidence. This chapter provides a broad overview of an untargeted ion mobility-mass spectrometry (IM-MS) workflow using a commercial drift tube ion mobility-quadrupole-time-of-flight mass spectrometer (IM-QTOF) for high confidence lipidomics.

Because the optimum working pressure of ion funnel (IF) is very close to the typical operating pressure of a traditional drift tube for proton transfer reaction mass spectrometry (PTR-MS), it is possible to develop an IF drift tube for PTR-MS to improve the sensitivity. In this study, an ion funnel capable of functioning as a drift tube in a PTR-MS system was designed and studied by computer simulation. To optimize the geometrical and electrical parameters of the ion funnel, five ion funnel configurations were constructed. The merits and features of the respective ion funnels were evaluated, and the ion transmission characteristics were investigated and analyzed. An optimized ion funnel model was compared against the typical traditional drift tube that was used in PTR-MS for ion transmission, and it was found that the ion traveling trajectories in the ion funnel and traditional drift tube had different shapes and ion transmission efficiencies. Preliminary investigations revealed that this ion funnel improved the ion transmission efficiency by at least 10 times. The simulation and experiment results are helpful in guiding the design of an improved ion funnel to develop a PTR-MS system with higher sensitivity.

As a step towards development of a high-resolution ion mobility mass spectrometer using the orbitrap mass analyzer platform, we describe herein a novel reverse-entry ion source (REIS) coupled to the higher-energy C-trap dissociation (HCD) cell of an orbitrap mass spectrometer with extended mass range. Development of the REIS is a first step in the development of a drift tube ion mobility-orbitrap MS. The REIS approach retains the functionality of the commercial instrument ion source which permits the uninterrupted use of the instrument during development as well as performance comparisons between the two ion sources. Ubiquitin (8.5 kDa) and lipid binding to the ammonia transport channel (AmtB, 126 kDa) protein complex were used as model soluble and membrane proteins, respectively, to evaluate the performance of the REIS instrument. Mass resolution obtained with the REIS is comparable to that obtained using the commercial ion source. The charge state distributions for ubiquitin and AmtB obtained on the REIS are in agreement with previous studies which suggests that the REIS-orbitrap EMR retains native structure in the gas phase.

The field of ion mobility-based omics studies requires high-quality collision cross section (CCS) libraries to effectively utilize CCS as a molecular descriptor. Absolute CCS values with the highest precision are obtained on drift tube instruments by measuring the drift time of ions at multiple drift voltages, commonly referred to as a ‘stepped field’ experiment. However, generating large scale absolute CCS libraries from drift tube instruments is time consuming due to the current lack of high-throughput methods. This communication reports a fully automated stepped-field method to acquire absolute CCS on commercially available equipment. Using a drift tube ion mobility-mass spectrometer (DTIM-MS) coupled to a minimally modified liquid chromatography (LC) system, CCS values can be measured online with a carefully timed flow injection analysis (FIA) experiment. Results demonstrate that the FIA stepped-field method yields CCS values which are of high analytical precision (< 0.4% relative standard deviation, RSD) and accuracy (≤ 0.4% difference) comparable to CCS values obtained using traditional direct-infusion stepped-field experiments. This high-throughput CCS method consumes very little sample volume (20 μL) and will expedite the generation of large-scale CCS libraries to support molecular identification within global untargeted studies.

Ion mobility spectrometry (IMS) is widely used to detect and identify chemical warfare agents, narcotics, and explosives in the field based on their reduced mobility (K 0 ) values. Current detection windows for these analytes can only be as narrow as ±2% of the K 0 values for the analyte being sought. These wide detection windows cause false positive alarms when an interferent with a similar reduced mobility falls within the detection window and triggers an alarm. This results in the loss of time and money as resources are diverted to verify the alarm. A high rate of false positive alarms is caused by a discrepancy in the reported K 0 values across the literature that is, at best, ± 2% of the average available values. By accurately and precisely measuring the variables affecting an ion’s K 0 value, an accurate K 0 value can be produced and the detection windows widths that are established using these reference values can be reduced. Components for accurate analyses have been assembled in the past and here the construction of an accurate ion mobility spectrometry drift tube is described that is accurate to 0.1% of the calculated K 0 value and can be hermetically sealed without inserting the drift tube into a large vacuum chamber. Having a pressure sealed accurate ion mobility spectrometer will allow for the control of the pressure variable within the K 0 equation and the safe analysis of hazardous chemicals. Here the construction of an inexpensive and easily reparable sealed drift tube is described.

Mobilities of polyatomic molecule ions in helium gas were measured at 85 K and room temperature using a low-temperature drift tube. They differed from the typical behavior shown by atomic or small molecular ions in helium owing to the influence of attractive interactions among the molecular ions and also their size and shape. To investigate the relationship between ion size and mobility, we measured the mobilities of CH 3 O + , C 2 H 5 O + , and C 3 H 7 O + .

Backgrounds Polymers, widely existing in food or dietary materials, have been attracting researchers, facing challenges, and needing effective strategies on targeted characterization in complex matrixes. Methods A modified data filtering strategy (including locating with drift time and m/z ranges, multiple mass defect filtering, validating MS information, and evaluating MS/MS spectra) was developed and applied for procyanidins in the grape seed extracts (GSE) using drift tube ion mobility-mass spectrometry. The procyanidin ions’ trendlines were predicted by multi-model regression. Their collision cross-sections (CCSs) were calculated using single-field methods. Results and discussion Totally, 769 CCSs belonging to 686 procyanidins with polymer degrees at 1–15 were characterized. The exponent regression was the most reasonable model (r2 ≥ 0.9379) to reveal the trendlines. The change tendency of CCSs with their polymer degrees, charge states, and linkage types were investigated. Conclusion This study provided an innovative strategy for targeted characterization of polymers in complex matrixes.

Glycosylated proteins are an essential class of molecules playing critical roles in complex biological systems. Understanding their biological functions remains extremely difficult due to the extremely broad compositions and structure variations of glycans. Although the combination of ion mobility spectrometry and mass spectrometry (IMS-MS) has become a promising technique in glycan structure characterization and composition identification, the insufficient resolving power of most IMS-MS instruments has limited its utility in performing the comprehensive structure characterization of glycans. To mitigate the low IMS resolving power, metal ion incorporation has been employed to enhance the separation of isomeric glycans. Here, we present a systematic investigation of many different glycan-metal ion complexes in an attempt to optimize the IMS separation of different isomeric glycans. By selecting optimum glycan-metal ion complexes, partial IMS separation was realized for all the 21 isomeric glycan pairs used in the experimental study. Baseline IMS separation was achieved for 76% of these isomeric glycan pairs. The best IMS separation of isomeric glycans was achieved in some cases by incorporating multiple ions with a glycan, such as the complex [glycan + Ca + Cl]+. In addition, the well-known IMS-MS measurement trendlines, often used to identify specific compound classes, were preserved for glycans even for all the 270 glycan-metal ion complexes observed in IMS-MS spectra.

Quantitation of the serum concentration of 25-hydroxyvitamin D is a high-demand assay that suffers from long chromatography time to separate 25-hydroxyvitamin D from its inactive epimer; however, ion mobility spectrometry can distinguish the epimer pair in under 30 ms due to the presence of a unique extended or "open" gas-phase sodiated conformer, not shared with the epimer, reducing the need for chromatographic separation. Five ion mobility mass spectrometers utilizing commercially available IMS technologies, including drift tube, traveling wave, trapped, and high-field asymmetric ion mobility spectrometry, are evaluated for their ability to resolve the unique open conformer. Additionally, settings for each instrument are evaluated to understand their influence on ion heating, which can drive the open conformer into a compact or "closed" conformer shared with the epimer. The four low-field instruments successfully resolved the open conformer from the closed conformer at baseline or near-baseline resolution at typical operating parameters. High-field asymmetric ion mobility was unable to resolve a unique peak but detected two peaks for the epimer, in contrast to the low-field methods that detected one conformer. This study seeks to expand the instrument space by highlighting the potential of each platform for the separation of 25-hydroxyvitamin D epimers.

The focus of this work was the implementation of ion mobility (IM) and a prototype quadrupole driver within data independent acquisition (DIA) using a drift tube IM-QTOFMS aiming to improve the level of confidence in identity confirmation workflows for non-targeted metabolomics. In addition to conventional all ions (IM-AI) acquisition, quadrupole resolved all ions (IM-QRAI) acquisition allows a drift time-directed precursor ion isolation in DIA using sequential isolation of precursor ions using mass windows of up to 100 Da which can be rapidly ramped across single ion mobility transients (i.e.,100 ms) according to the arrival times of precursor ions. Both IM-AI and IM-QRAI approaches were used for identity confirmation and relative quantification of metabolites in cellular extracts of the cell factory host Pichia pastoris. Samples were spiked with a uniformly

Ions in an IMS are mostly clustered or hydrated so that a single ion mobility peak usually contains a mixture of ions differing in their cluster size. In this study, a model is used to describe the average mobility and drift time based on the individual properties of the mixture. For this purpose, the following four fraction quantities are defined: length fraction, X i d , (i.e., the fraction of the drift tube along which the ion travels in the form of i); time fraction, X i t , (i.e., the fraction of the drift time during which the ion travels in the form of i); single ion time fraction, X i t o , (i.e., the time an ion spends as i in the drifting mixture divided by the drift time of pure i); and the mole fraction, Xi. It is shown that for a binary mixture of ions, the fraction quantities are related by ( X A = X A t ) = ( X A d = X A t o ) × ( X A + α . X B ) , where α=KA/KB is the relative mobility of the two components. It is concluded that average mobility is related to the single ion mobilities in the form of K a v g = X 0 K 0 + X 1 K 1 + X 2 K 2 + .. . ., where, Xi is the mole fraction. However, the observed or the average drift time cannot be described in a similar manner. Rather, it must be inverted to tobs−1 = Xoto−1 + X1t1−1 + X2t2−1 + …. If, in case, it is expanded as tobs = αo to+ α1 t1+ α2 t2+ …, the coefficient αi will differ from the mole fractions.

The mobilities of polyatomic molecular ions in He gas, measured at 83 and 306 K using a low-temperature drift tube, were smaller than the polarization limit K pol. The mobilities of atomic or small molecular ions tended to show a bump at intermediate reduced field, and then approach the polarization limit at low reduced field; however, the measured mobilities of polyatomic molecular ions were different. We compared the experimental mobilities with values calculated using the MOBCAL program, and found that they agreed well.

Miniaturized low-cost drift tubes with high analytical performance are a key component for the design of powerful and mass-deployable hand-held ion mobility spectrometers. Thus, a simple model that estimates the influence of the geometrical dimensions on the analytical performance is highly desirable for an effective design process. In this work, we present a simple procedure to predict peak distortion based on only the electrical field distribution inside the drift tube, which can be rapidly simulated using the finite element method. A simulation of the ion motion is not required. Based on these results, we developed an ion mobility spectrometer manufactured entirely from standard printed circuit boards (PCB). Since no additional components were used apart from electrical and gas connectors, ion source and metal grids, the presented ion mobility spectrometer is very simple and inexpensive. Nevertheless, the design provides a resolving power of 82 at a drift length of 50 mm and a drift voltage of 3 kV using a tritium ion source and a field switching shutter. The limits of detection for one second of averaging are 80 pptv for acetone, 35 pptv for dimethyl methylphosphonate and 180 pptv for methyl salicylate. The final publication is available at Springer via https://doi.org/10.1007/s12127-016-0202-7.

A V-shaped ion funnel (IF) drift tube was developed for proton transfer reaction mass spectrometry (PTR-MS). The ion transmissions were characterized at variable radio frequency voltages and frequencies to obtain optimized conditions while considering the effects of radial-focusing, reaction rate, and collision-induced dissociation. The improvements in sensitivity for common compounds were experimentally obtained and ranges from 2 to 22 times depending on the analyte. The product ions distributions were also studied for V-shaped IF PTR-MS. Together with the literature reports for U-shaped IF PTR-MS, a valuable and comprehensive reference is provided for future optimization of IF PTR-MS and other mass spectrometers.

Developing powerful hand-held drift tube ion mobility spectrometers (IMS) requires small, lightweight drift tubes with high analytical performance. In this work, we present an easy-to-manufacture, miniaturized drift tube ion mobility spectrometer, which is manufactured from polyether ether ketone, stainless steel foils and printed circuit boards. It is possible to operate the drift tube IMS with a radioactive 3H ionization source or a non-radioactive X-ray ionization source with 3 kV acceleration voltage. The drift tube design provides high resolving power of Rp = 63 at a drift length of just 40 mm, 15 mm × 15 mm in cross-section (outer dimensions) and a drift voltage of 2.5 kV. The limits of detection for less than one second of averaging are 40 pptv for dimethyl-methylphosphonate and 30 pptv for methyl salicylate. For demonstration, the miniaturized drift tube IMS is integrated into a stand-alone battery-powered mobile device, including a closed gas-loop, high performance driver electronics and wireless data transmission. In a proof-of-concept study, this device was tested in an international field evaluation exercise to detect the release of a volatile, hazardous substance inside a large entry hall.

This chapter provides a broad overview of ion mobility-mass spectrometry (IM-MS) and its applications in separation science, with a focus on pharmaceutical applications. A general overview of fundamental ion mobility (IM) theory is provided with descriptions of several contemporary instrument platforms which are available commercially (i.e., drift tube and traveling wave IM). Recent applications of IM-MS toward the evaluation of structural isomers are highlighted and placed in the context of both a separation and characterization perspective. We conclude this chapter with a guided reference protocol for obtaining routine IM-MS spectra on a commercially available uniform-field IM-MS.

Rationale In medicine and drug development, molecular modelling is an important tool. It is attractive to develop a platform connecting the theoretical structural modelling and the results from experimental measurement. In addition, the separation and structural analysis of bioactive constituent isomers are still challenging tasks. Methods Drift tube ion mobility (IM) mass spectrometry (MS) provides the experimental collision cross section (CCS) which contains the structural information. The experimental CCS can be compared with the calculated CCS of the molecular modelling structures. This technique is especially useful for bioactive constituents in herbal medicine because active isomers with the same chemical formula are common in these samples. IM helps separate and identify these isomers and reveals details about their structures and conformations. Results Two model bioactive constituents, caffeoylquinic acids (CQAs) and dicaffeoylquinic acids (di-CQAs), were selected to systematically investigate the influence of solution, ion source conditions and ion heating on the isomer CCS distributions. By comparing the calculated CCS with the experimental value, we identified the favorable conformations of CQAs. The most compact conformation of a CQA was less likely to isomerize than the more extended conformation. It was found that the isomerization tendency was in accord with the conformation favorability. Conclusions This study offers an effective approach to predict and demystify the conformation and isomerization of the active constituents in herbal medicines.

RATIONALE Polyoxometalates (POMs) are remarkable oxo-clusters forming compact highly charged anions. We measured their collision cross sections (CCS) in N2 with drift tube ion mobility spectrometry (DTIMS). These values were then used to calibrate a traveling wave ion mobility spectrometry (TWIMS) device and the accuracy of the calibration was tested. METHODS Six POM standards were analyzed by DTIM-MS (Tofwerk, Thun, Switzerland) at different voltages to determine absolute DT CCS (N2 ) values. Five POM compounds (Lindqvist TBA2 Mo6 O19; decatungstate TBA4 W10 O32; Keggin TBA3 PMo12 O40 ; TBA3 PW12 O40 and Dawson TBA6 P2 W18 O62 ) were used for the calibration of the TWIM-MS instrument (Synapt G2 HDMS, Waters, Manchester, UK) and a sixth Dawson POM, TBA9 P2 Nb3 W15 O62 , was used to compare the accuracy of the calibrations with POM or with polyalanine and dextran reference ions. RESULTS We determined 45 DT CCS (N2 ) values at 30°C or 60°C. Fourteen DT CCS (N2 ) values at 30°C were used to perform calibration of the TWIMS instrument. Better correlations were observed than when DT CCS values in helium from the literature were used. The accuracy tests on six ions of Dawson POM TBA9 P2 Nb3 W15 O62 led to relative errors below 3.1% while relative errors of 3.6% to 10.1% were observed when calibration was performed with polyalanine and dextran reference ions. CONCLUSIONS Our novel calibration strategy for determination of CCS values of multiply negatively charged ions on TWIM-MS devices based on DT CCS (N2 ) of standard POM structures covered a wider range of CCS and improved the accuracy to 2.1% relative error on average compared with 6.9% using polyalanine and dextran calibration.

International audience; Over the years, polymer analyses using ion mobility-mass spectrometry (IM-MS) measurements have been performed on different ion mobility spectrometry (IMS) setups. In order to be able to compare literature data taken on different IM(-MS) instruments, ion heating and ion temperature evaluations have already been explored. Nevertheless, extrapolations to other analytes are difficult and thus straightforward same-sample instrument comparisons seem to be the only reliable way to make sure that the different IM(-MS) setups do not greatly change the gas-phase behavior. We used a large range of degrees of polymerization (DP) of poly(ethylene oxide) PEO homopolymers to measure IMS drift times on three different IM-MS setups: a homemade drift tube (DT), a trapped (TIMS), and a traveling wave (T-Wave) IMS setup. The drift time evolutions were followed for increasing polymer DPs (masses) and charge states, and they are found to be comparable and reproducible on the three instruments.

One of the most common volatile organic compounds (VOCs) group is monoterpenes. Monoterpenes share the molecular formula C10H16, they are usually cyclic and have a pleasant smell. The most common monoterpenes are limonene (present in citrus fruits) and α-pinene (present in conifers’ resin). Different monoterpenes have different chemical, biological and ecological properties thus it is experimentally very important to be able to differentiate between them in real time. Real time instruments such as Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-ToF-MS), offer a real time solution for monoterpene measurement but at the cost of selectivity resulting in all monoterpenes being seen at the same m/z. In this work we used Selective Reagent Ion-Time of Flight-Mass Spectrometry (SRI/PTR-ToF-MS) in order to explore the differences in ion branching when different ionizations (H3O+, NO+ and O2 +) and different drift tube reduced field energies (E/N) were used. We report a comprehensive ion library with many unique features, characteristic for individual monoterpenes.

Mobilities of C3H7O+ ions in He and Ne gas were measured at 85 K and room temperature using a low-temperature drift tube. The effects of structural isomerism on mobility were investigated by comparing C3H7O+ fragments generated by electron impact from 2-butanol ((s)-C3H7O+) and tert-butanol ((t)-C3H7O+). In He at 85 K, the mobility of (t)-C3H7O+ was about 5% less than that of (s)-C3H7O+. Furthermore, to investigate the effects of polarized interactions on ionic structural isomers, measurements in He and Ne buffer gases were compared. The mobilities in Ne were the same at all the tested temperatures.

The characterization of the release of aroma compounds from beverages can bring pertinent information that can help in better understanding aroma perception. However, this kind of measurement is complex for high ethanol-containing beverages and needs to be adapted or optimized. Increasing the mean collision energy in the drift tube via the E / N ratio can be an interesting solution to prevent H 3 O + depletion when high ethanol-containing samples, as distilled beverages for instance, are analyzed. However, the higher collision energy induced by these conditions impacts ionization reactions due to an increased number of fragmentation mechanisms, which could make data analysis difficult. The aim of the present study was to highlight the pertinence of using strong operating conditions ( E / N = 454 Td) compared to reference conditions ( E / N = 120–140 Td) for the analysis of 40% (v/v) ethanol-containing beverages. The first step was to better understand product ion distributions of 11 aroma compounds, known to be important for the overall flavor of brandies and prepared in 40% (v/v) ethanol/water solutions, at both operating conditions. As a validation, eight commercial brandies from different brands and with different aging times were analyzed under the two operating conditions. It appeared that the E / N value did not impact product ion distribution, but changed their relative abundances: increasing the E / N ratio increased fragmentation mechanisms, resulting in the detection of a greater proportion of low mass fragments to the detriment of protonated ions issued from aroma compounds. The response linearity of the PTR-MS was not modified at strong operating conditions. The application of these conditions to the analysis of brandies highlighted that, in spite of modifications on ionization mechanisms, products can be correctly discriminated, mainly according to their aging time.

The problem of hazardous industrial chemicals ions separation with close mobility by IMS method has identified the need of design and drift tube electrical parameters modeling to ensure the ion transport. A simulation of IMS drift tube electric field was performed and the trajectories of the ions in the region of ionization source electrodes, in the ionization region and in the drift region of IMS tube was shown. Obtained results have allowed to estimate influence of inhomogeneity of the field in the drift region on the resolution of the ion mobility spectrometer, as well as to make changes in the parameters of the tube to minimize this impact. Based on the performed modeling have been identified best constructive decisions for the manufacture of drift tubes. On the manufactured drift tube been successfully carried out the experimental detection of hazardous industrial chemicals.

A new ion trapping technique, involving the accumulation of ions in a cyclical drift tube, as a means of enhancing ion signals for scanning ion cyclotron mobility measurements has been modeled by computational simulations and demonstrated experimentally. In this approach, multiple packets of ions are periodically released from a source region into the on ramp region of the cyclical drift tube and these pulses are accumulated prior to initiation of the mobility measurements. Using this ion trapping approach, it was possible to examine ions that traversed between 1.83 and 182.86 m (from 1 to 100 cycles). Overall, we observe that instrumental resolving power improves with increasing cycle numbers; at 100 cycles, a resolving power in excess of 1000 can be achieved. The utility of this method as a means of distinguishing between analytes is demonstrated by examining the well-characterized model peptides substance P, angiotensin II, and bradykinin.

The drift voltage is one of the key experimental parameters of any drift tube ion mobility spectrometer. In this work, we show that a universal relationship between optimum drift voltage and the resolving power reached at this point exists, governed only by temperature and ion charge state. With these two quantities known, the measured optimum drift voltage and resolving power combination can be used to estimate the ideality of the drift conditions inside a drift tube, since any deviation from the theoretical values must be caused by non-idealities in the ions’ drift. Analyzing drift voltage sweeps from nine different ion mobility spectrometers, a continuous increase in drift tube ideality over the past is observed, reaching from less than 50% thirty years ago to 99% for a current design based on printed circuit boards. Furthermore, possible causes for the observed non-idealities are discussed. The final publication is available at Springer via https://doi.org/10.1007/s12127-017-0219-6.

A method for relating traveling-wave ion mobility spectrometry (TWIMS) drift times with collisional cross-sections using computational simulations is presented. This method is developed using SIMION modeling of the TWIMS potential wave and equations that describe the velocity of ions in gases induced by electric fields. The accuracy of this method is assessed by comparing the collisional cross-sections of 70 different reference ions obtained using this method with those obtained from static drift tube ion mobility measurements. The cross-sections obtained here with low wave velocities are very similar to those obtained using static drift (average difference = 0.3%) for ions formed from both denaturing and buffered aqueous solutions. In contrast, the cross-sections obtained with high wave velocities are significantly greater, especially for ions formed from buffered aqueous solutions. These higher cross-sections at high wave velocities may result from high-order factors not accounted for in the model presented here or from the protein ions unfolding during TWIMS. Results from this study demonstrate that collisional cross-sections can be obtained from single TWIMS drift time measurements, but that low wave velocities and gentle instrument conditions should be used in order to minimize any uncertainties resulting from high-order effects not accounted for in the present model and from any protein unfolding that might occur. Thus, the method presented here eliminates the need to calibrate TWIMS drift times with collisional cross-sections measured using other ion mobility devices. Graphical Abstract ᅟ.

The technique of ion mobility spectrometry (IMS) offers a practical and fast detecting method in ambient conditions to estimate whether there may presence contrabands or even chemical warfare agents (CWAs). In this work we have investigated a self-made radioactive 63Ni (β emission) ionization source for ion mobility spectrometry employed with an atmospheric pressure to detect real CWAs, such as GB, GD, HD, VX from aerosol samples. Furthermore, we have experimentally studied the influence of drift tube temperature not only in ion cluster formation in the positive mode, but also the detection limitation of CWAs.

The J-PARC linac has three DTL tanks to accelerate the negative hydrogen ions from 3 MeV to 50 MeV. The RF phase and amplitude are adjusted for each cavity with a phase scan method within the accuracy of 1? in phase and 1% in amplitude. The experimental results show a remarkable agreement with the numerical model within a sufficient margin in the tuning of the last two DTL tanks. However, a notable discrepancy between the experiment and the numerical model is seen in the tuning of the first DTL tank. After studying with a three-dimensional multi-particle simulation, the generation of the low energy component and the pronounced filamentation are identified as the main causes of the discrepancy. The optimization of the tuning scheme is also discussed to attain the tuning goal accuracy for the first DTL tank.

Performance of several time-of-flight (TOF) type ion mobility spectrometers (IMS) was compared in a joint measurement campaign and their mobility scales were adjusted based on the measurements. A standard reference compound 2,6-di-tert butylpyridine (2,6-DtBP) was used to create a single peak ion mobility distribution with a known mobility value. The effective length of the drift tube of each device, considered here as an instrument constant, was determined based on the measurements. Sequentially, two multi-peaked test compounds, DMMP and DIMP, were used to verify the performance of the adjustment procedure in a wider mobility scale. By determining the effective drift tube lengths using 2,6-DtBP, agreement between the devices was achieved. The determination of effective drift tube lengths according to standard reference compound was found to be a good method for instrument inter-comparison. The comparison procedure, its benefits and shortcomings as well as dependency on accuracy of literature value are discussed along with the results.

Transmission through a drift tube has been measured for different types of ions. Various ions were injected at the same rate at the start of the drift tube. Then, the transmitted currents were measured at the end of the drift tube. The results show that transmission depends linearly on the inverse of the drift time. Factors influencing the drift time, such as pressure, temperature, and electric field, were also investigated and shown to affect the transmission efficiency in a similar manner as the type of ion. A simple model based on kinetics of two parallel processes (loss or transmission) is proposed to explain the results. Since slow-moving ions are lost more often than fast-moving ones, the intensity of ion peaks decreases as drift time increases. This can be easily corrected by transforming the y-axis to y × x (i.e., intensity × drift time). © 2008 Elsevier B.V. All rights reserved.

Design and electrodynamic characteristics of the accelerating interdigital structure have been calculated in the 3D version. Inductance–capacitance-type tuners (“contrivance”) have been developed in the form of rods located on the drift tube side, which is opposite to the setting stems. It is demonstrated that the interdigital accelerating structure can be tuned with the use of this simple and efficient system only.

Characteristics of the mass spectra of C 1 –C 5 alkyl nitrates (RONO 2 ) were systematically examined with a proton transfer reaction time-of-flight mass spectrometer operated at field strengths, E / N , of the drift tube of between 96 and 147 Td. Although protonated alkyl nitrates were detected for C 1 –C 4 alkyl nitrates, their signal intensities were, at most, a few percent of the total ion signals. The major product ions were several fragment ions including NO 2 + , RO + , R + , and ROH·H + , the abundances and relative intensities of which depended on the E / N ratio. The intensity of NO 2 + ions increased with increasing E / N ratio, whereas the intensities of organic fragments such as R + and RO + ions, relative to the total product ions, decreased with increasing E / N ratio. Those organic fragment ions partly underwent further fragmentation at high E / N ratios to produce [R − 2H] + , [R − 4H] + , and [RO − 2H] + , particularly for the higher alkyl nitrates. The fragmentation patterns also varied for the C 1 –C 5 alkyl nitrates, the most predominant ions being the NO 2 + for C 1 –C 2 alkyl nitrates and R + ions for C 3 –C 5 alkyl nitrates. Although the experimental finding that NO 2 + fragment ions were detected regardless the speciation of alkyl nitrates suggested that the detection of C 1 –C 2 alkyl nitrates by this technique is not selective, the abundant fragment ion signals of R + ions could be useful for the identification of C 3 –C 5 alkyl nitrates.

Multidimensional high throughput separations are ideal for analyzing distinct ion characteristics simultaneously in one analysis. We report on the first evaluation of a platform coupling a high speed field asymmetric ion mobility spectrometry microchip (μFAIMS) with drift tube ion mobility and mass spectrometry (IMS-MS). The μFAIMS/IMS-MS platform was used to analyze biological samples and simultaneously acquire multidimensional FAIMS compensation fields, IMS drift times, and accurate ion masses for the detected features. These separations thereby increased the overall measurement separation power, resulting in greater information content and more complete characterization of the complex samples. The separation conditions were optimized for sensitivity and resolving power by the selection of gas compositions and pressures in the FAIMS and IMS separation stages. The resulting performance provided three dimensional separations, benefitting both broad complex mixture studies and targeted analyses by improving isomeric separations and allowing detection of species obscured by interfering peaks.

The development of a new ion mobility/mass spectrometry instrument that incorporates a multifield drift tube/ion funnel design is described. In this instrument, individual components from a mixture of ions can be resolved and selected on the basis of mobility differences prior to collisional activation inside the drift tube. The fragment ions that are produced can be dispersed again in a second ion mobility spectrometry (IMS) region prior to additional collisional activation and MS analysis. The result is an IMS-IMS analogue of MS-MS. Here, we describe the preliminary instrumental design and experimental approach. We illustrate the approach by examining the highly characterized bradykinin and ubiquitin systems. Mobility-resolved fragment ions of bradykinin show that b-type ions are readily discernible fragments, because they exist as two easily resolvable structural types. Current limitations and future directions are briefly discussed.

A field modulation approach for high-throughput ion mobility/time-of-flight analyses of complex mixtures has been developed using a split-field drift tube. In this approach, complex mixtures of peptides, such as those that arise from tryptic digestion of protein mixtures, are separated by nanocolumn liquid chromatography, ionized by electrospray ionization, and analyzed by ion mobility/ time-of-flight techniques. The split-field drift tube allows parent ions to be separated based on differences in their low-field mobilities through the first-field region before entering the second region. For increased throughput, the magnitude of the field in the second region can be modulated throughout an LC separation in order to favor transmission of different types of ions: parent ions at low fields; fragments from primarily [M+3H] 3+ peptides at moderate fields; or, fragmentation of [M+3H] 3+ and [M+2H] 2+ species at higher fields. We demonstrate the approach with two examples: a mixture of tryptic peptides from digestion of hemoglobin; and a complex mixture of tryptic peptides from digestion of human plasma.

Ion mobility measurements have been performed for protonated polyalanine peptides (A10 + H+, A15 + H+, A20 + H+, A25 + H+, and A15NH2 + H+) as a function of temperature using a new high-temperature drift tube. Peaks due to helices and globules were found at room temperature for all peptides, except for A10 + H+ (where only the globule is present). As the temperature is increased, the helix and globule peaks broaden and merge to give a single narrow peak. This indicates that the two conformations interconvert rapidly at elevated temperatures. The positions of the merged peaks show that A15 + H+ and A15NH2 + H+ spend most of their time as globules when heated, while A20 + H+ and A25 + H+ spend most of their time as helices. The helix/globule transitions are almost certainly accompanied by intramolecular proton transfer, and so, these results suggest that the proton becomes mobile (able to migrate freely along the backbone) at around 450 K. The peptides dissociate as the temperature is increased further to give predominantly the bn(+), b(n-1)(+), b(n-2)(+), ... series of fragment ions. There is a correlation between the ease of fragmentation and the time spent in the helical conformation for the An + H+ peptides. Helix formation promotes dissociation because it pools the proton at the C-terminus where it is required for dissociation to give the observed products. In addition to the helix and globule, an antiparallel helical dimer is observed for the larger peptides. The dimer can be collisionally dissociated by injection into the drift tube at elevated kinetic energies.

Quenching rate constants for NO+(v=1) and NO+(v=4) in collisions with Ar have been measured from near thermal energy up to 0.5 eV mean relative kinetic energy in a selected ion flow drift tube. The rate constants increase dramatically with KECM indicating that the quenching is dominated by the short range repulsive interaction. At higher energies the data fit linear Landau–Teller plots. These are the first L–T plots obtained for ion quenching by other than a He quencher.

One of the key experimental parameters of measurements using a drift tube ion mobility spectrometer is the drift voltage applied across its length, as it governs a multitude of processes during the ion drift. While the effect of the drift voltage on the resolving power has already been well-described, only little attention has been paid so far to developing an equally sophisticated model for the effect on the limits of detection. In this work, we extend our previous model for the resolving power and signal-to-noise-ratio of a drift tube ion mobility spectrometer operated at the resolving power optimal drift voltage to arbitrary drift voltages. It is shown that the deviation from this operating point can be completely described for any drift tube by using only the dimensionless factor β, which is defined as the ratio between the applied drift voltage and the resolving power optimal drift voltage. From these general equations, it can be shown that the signal-to-noise-ratio and therefore the limits of detection vary much more significantly with changing drift voltage than the resolving power. Thus, it is possible to apply a higher than resolving power optimal drift voltage to lower the limits of detection with only a slight loss of resolving power. E.g., a 47.5 % higher drift voltage is able to halve the limits of detection, but yields only 8 % resolving power loss. The final publication is available at Springer via https://doi.org/10.1007/s12127-015-0176-x.

A technique for finding the electric field dependence of the coefficient of ion mobility in gases is suggested. For ions of 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, 1,3,5-trinitrobenzene, 1,3-dinitrobenzene, and dimethylmethylphosphonate, these dependences are taken in air by applying a variable periodic polarity-asymmetric specially shaped electric field. The accuracy of the technique suggested is estimated and compared with that of the conventional drift tube method.

The structures of a series of quadruply protonated polyalanine peptides ([Ala n + 4H] 4 + , n = 29-49) have been examined in the gas phase using high-pressure drift tube/mass spectrometry and molecular modeling techniques.The results indicate that [Ala n + 4H] 4 + ions favor stretched helices; i → i + 3 and i → i + 4 hydrogen-bonding interactions are significant in stabilizing the extended structures. Experiment and theory indicate that the fraction of i → i + 4 interactions increases with increasing polymer length. It appears that i → i + 3 interactions stabilize smaller polymers, where repulsive Coulombic interactions are greater. For [Ala 3 6 + 4H] 4 + , ∼35% of hydrogen-bonding interactions are associated with i → i + 3 contacts, while ∼65% correspond to i → i + 4 associations. In the larger [Ala 4 8 + 4H] 4 + polymer, ∼85% of residues are involved in i → i + 4 hydrogen-bonding interactions.

A flowing afterglow-selected ion flow drift tube has been used to measure the rate coefficients and product ion distributions for reactions of H3O+, N2H+, and H3+ with a series of 16 alkanes, alken...

We have studied a compact heavy-ion linac for atomic physics and medical use. The design of the linac was based on using alternating-phase-focus (APF) and interdigital-H (IH) structures which give sufficient electric power efficiency. Thereby, it will be possible to design a small and high efficiency linac. The APF-IH linac was designed to accelerate ions from C2+ to U40+, from 30 to 300 keV/u and an operating frequency of 100 MHz. We made a half-scale cold model of this linac using orbit calculation and measured its RF characteristics. Then, we designed a APF-IH type linac using the results of the measurement.