Coupling of capillary electrophoresis with electrospray ionization multiplexing ion mobility spectrometry

In this work, ion mobility spectrometry (IMS) function as a detector and another dimension of separation was coupled with CE to achieve two‐dimensional separation. To improve the performance of hyphenated CE‐IMS instrument, electrospray ionization correlation ion mobility spectrometry is evaluated and compared with traditional signal averaging data acquisition method using tetraalkylammonium bromide compounds. The effect of various parameters on the separation including sample introduction, sheath fluid of CE and drift gas, data acquisition method of IMS were investigated. The experimental result shows that the optimal conditions are as follows: hydrodynamic sample injection method, the electrophoresis voltage is 10 kilo volts, 5 mmol/L ammonium acetate buffer solution containing 80% acetonitrile as both the background electrolyte and the electrospray ionization sheath fluid, the ESI liquid flow rate is 4.5 μL/min, the drift voltage is 10.5 kilo volts, the drift gas temperature is 383 K and the drift gas flow rate is 300 mL/min. Under the above conditions, the mixture standards of seven tetraalkylammoniums can be completely separated within 10 min both by CE and IMS. The linear range was 5–250 μg/mL, with LOD of 0.152, 0.204, 0.277, 0.382, 0.466, 0.623 and 0.892 μg/mL, respectively. Compared with traditional capillary electrophoresis detection methods, the developed CE‐ESI‐IMS method not only provide two sets of qualitative parameters including electrophoresis migration time and ion drift time, ion mobility spectrometer can also provide an additional dimension of separation and could apply to the detection ultra‐violet transparent compounds or none fluorescent compounds.     

In situ isobaric lipid mapping by MALDI–ion mobility separation–mass spectrometry imaging

The highly diverse chemical structures of lipids make their analysis directly from biological tissue sections extremely challenging. Here, we report the in situ mapping and identification of lipids in a freshwater crustacean Gammarus fossarum using matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) in combination with an additional separation dimension using ion mobility spectrometry (IMS). The high‐resolution trapped ion mobility spectrometry (TIMS) allowed efficient separation of isobaric/isomeric lipids showing distinct spatial distributions. The structures of the lipids were further characterized by MS/MS analysis. It is demonstrated that MALDI MSI with mobility separation is a powerful tool for distinguishing and localizing isobaric/isomeric lipids.     

Ion mobility spectrometry detection for gas chromatography

The hyphenated analytical method in which ion mobility spectrometry (IMS) is coupled to gas chromatography (GC) provides a versatile alternative for the sensitive and selective detection of compounds after chromatographic separation. Providing compound selectivity by measuring unique gas phase mobilities of characteristic analyte ions, the separation and detection process of gas chromatography-ion mobility spectrometry (GC-IMS) can be divided into five individual steps: sample introduction, compound separation, ion generation, ion separation and ion detection. The significant advantage of a GC-IMS detection is that the resulting interface can be tuned to monitor drift times/ion mobilities (as a mass spectrometer (MS) can be tuned to monitor ion masses) of interest, thereby tailoring response characteristics to fit the need of a given separation problem. Because IMS separates ions based on mobilities rather than mass, selective detection among compounds of the same mass but different structures are possible. The most successful application of GC-IMS to date has been in the international space station. With the introduction of two-dimensional gas chromatography (2D-GC), and a second type of mobility detector, namely differential mobility spectrometry (DMS), GC prior to mobility measurements can now produce four-dimensional analytical information. Complex mixtures in difficult matrices can now be analyzed. This review article is intended to provide an overview of the GC-IMS/DMS technique, recent developments, significant applications, and future directions of the technique.     

Metabolic profiling of Escherichia coli by ion mobility-mass spectrometry with MALDI ion source

Comprehensive metabolome analysis using mass spectrometry (MS) often results in a complex mass spectrum and difficult data analysis resulting from the signals of numerous small molecules in the metabolome. In addition, MS alone has difficulty measuring isobars and chiral, conformational and structural isomers. When a matrix-assisted laser desorption ionization (MALDI) source is added, the difficulty and complexity are further increased. Signal interference between analyte signals and matrix ion signals produced by MALDI in the low mass region (<1500 Da) cause detection and/or identification of metabolites difficult by MS alone. However, ion mobility spectrometry (IMS) coupled with MS (IM-MS) provides a rapid analytical tool for measuring subtle structural differences in chemicals. IMS separates gas-phase ions based on their size-to-charge ratio. This study, for the first time, reports the application of MALDI to the measurement of small molecules in a biological matrix by ion mobility-time of flight mass spectrometry (IM-TOFMS) and demonstrates the advantage of ion-signal dispersion in the second dimension. Qualitative comparisons between metabolic profiling of the Escherichia coli metabolome by MALDI-TOFMS, MALDI-IM-TOFMS and electrospray ionization (ESI)-IM-TOFMS are reported. Results demonstrate that mobility separation prior to mass analysis increases peak-capacity through added dimensionality in measurement. Mobility separation also allows detection of metabolites in the matrix-ion dominated low-mass range (m/z < 1500 Da) by separating matrix signals from non-matrix signals in mobility space.     

Optimum collision energies for proteomics: The impact of ion mobility separation

Ion mobility spectrometry (IMS) is a widespread separation technique used in various research fields. It can be coupled to liquid chromatography–mass spectrometry (LC–MS/MS) methods providing an additional separation dimension. During IMS, ions are subjected to multiple collisions with buffer gas, which may cause significant ion heating. The present project addresses this phenomenon from the bottom-up proteomics point of view. We performed LC–MS/MS measurements on a cyclic ion mobility mass spectrometer with varied collision energy (CE) settings both with and without IMS. We investigated the CE dependence of identification score, using Byonic search engine, for more than 1000 tryptic peptides from HeLa digest standard. We determined the optimal CE values—giving the highest identification score—for both setups (i.e., with and without IMS). Results show that lower CE is advantageous when IMS separation is applied, by 6.3 V on average. This value belongs to the one-cycle separation configuration, and multiple cycles may supposedly have even larger impact. The effect of IMS is also reflected in the trends of optimal CE values versus m/z functions. The parameters suggested by the manufacturer were found to be almost optimal for the setup without IMS; on the other hand, they are obviously too high with IMS. Practical consideration on setting up a mass spectrometric platform hyphenated to IMS is also presented. Furthermore, the two CID (collision induced dissociation) fragmentation cells of the instrument—located before and after the IMS cell—were also compared, and we found that CE adjustment is needed when the trap cell is used for activation instead of the transfer cell. Data have been deposited in the MassIVE repository (MSV000090944).     

Multidimensional Mass Spectrometry of Synthetic Polymers and Advanced Materials

Multidimensional mass spectrometry interfaces a suitable ionization technique and mass analysis (MS) with fragmentation by tandem mass spectrometry (MS²) and an orthogonal online separation method. Separation choices include liquid chromatography (LC) and ion‐mobility spectrometry (IMS), in which separation takes place pre‐ionization in the solution state or post‐ionization in the gas phase, respectively. The MS step provides elemental composition information, while MS² exploits differences in the bond stabilities of a polymer, yielding connectivity and sequence information. LC conditions can be tuned to separate by polarity, end‐group functionality, or hydrodynamic volume, whereas IMS adds selectivity by macromolecular shape and architecture. This Minireview discusses how selected combinations of the MS, MS², LC, and IMS dimensions can be applied, together with the appropriate ionization method, to determine the constituents, structures, end groups, sequences, and architectures of a wide variety of homo‐ and copolymeric materials, including multicomponent blends, supramolecular assemblies, novel hybrid materials, and large cross‐linked or nonionizable polymers.     

One-dimensional and comprehensive two-dimensional gas chromatography coupled to soft photo ionization time-of-flight mass spectrometry: a two- and three-dimensional separation approach

Soft laser photo-ionization mass spectrometry is presented as a separation dimension hyphenated with gas chromatographic techniques. Single photon ionization (SPI) is a universal soft ionization method which ionizes organic molecules with an ionization potential below 10.5 eV if 118 nm laser radiation is used. The inherently soft ionization of photo ionization techniques can further be utilized together with gas chromatography as a comprehensive two-dimensional separation method (GC x MS), using the GC retention time as first separation dimension and the molecular mass as second separation dimension. Some GC x MS chromatograms of diesel petroleum samples using SPI are presented and discussed. Finally, it is demonstrated that the coupling of soft SPI mass spectrometry with comprehensive two-dimensional gas chromatography (GC x GC) provides a three-dimensional separation technique (GC x GC x SPI-MS).     

Sterically hindered phenols in negative ion mobility spectrometry–mass spectrometry

Negative corona discharge atmospheric pressure chemical ionization (APCI) was used to investigate phenols with varying numbers of tert‐butyl groups using ion mobility spectrometry–mass spectrometry (IMS‐MS). The main characteristic ion observed for all the phenolic compounds was the deprotonated molecule [M–H]⁻. 2‐tert‐Butylphenol showed one main mobility peak in the mass‐selected mobility spectrum of the [M–H]⁻ ion measured under nitrogen atmosphere. When air was used as a nebulizer gas an oxygen addition ion was seen in the mass spectrum and, interestingly, this new species [M–H+O]⁻ had a shorter drift time than the lighter [M–H]⁻ ion. Other phenolic compounds primarily produced two IMS peaks in the mass‐selected mobility spectra measured using the [M–H]⁻ ion. It was also observed that two isomeric compounds, 2,4‐di‐tert‐butylphenol and 2,6‐di‐tert‐butylphenol, could be separated with IMS. In addition, mobilities of various characteristic ions of 2,4,6‐trinitrotoluene were measured, since this compound was previously used as a mobility standard. The possibility of using phenolic compounds as mobility standards is also discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Separation of benzodiazepines by electrospray ionization ion mobility spectrometry-mass spectrometry

Benzodiazepines are a commonly abused class of drugs; requiring analytical techniques that can separate and detect the drugs in a rapid time period. In this paper, the two-dimensional separation of five benzodiazepines was shown by electrospray ionization (ESI) ion mobility spectrometry (IMS)-mass spectrometry (MS). In this study, both the two dimensions of separation (m/z and mobility) and the high resolution of our IMS instrument enabled confident identification of each of the five benzodiazepines studied. This was a significant improvement over previous IMS studies that could not separate many of the analytes due to low instrumental resolution. The benzodiazepines that contain a hydroxyl group in their molecular structure (lorazepam and oxazepam) were found to form both the protonated molecular ion and dehydration product as predominant ions. Experiments to isolate the parametric reasons for the dehydration ion formation showed that it was not the result of corona discharge processes or the potential applied to the needle. However, the potential difference between the needle and first drift ring did influence both the relative intensity ratios of the two ions and the ion sensitivity.     

一种基于离子迁移谱的气相色谱检测器及其应用

离子迁移谱作为气相色谱的检测器,兼有色谱的高分离能力和离子迁移谱的高灵敏度,有利于实现复杂混合物的实时在线监测。基于在色谱、离子迁移谱方面的研究基础,本实验室搭建了一套以离子迁移谱为检测器的气相色谱仪,分别对检测器的温度、总电压、尾吹气流速等参数进行了系统优化,并用于碘甲烷、1,2-二氯乙烷、四氯化碳和二溴甲烷4种卤代烃化合物的检测。实验结果表明,参数优化后的离子迁移谱检测器对碘甲烷、1,2-二氯乙烷、四氯化碳和二溴甲烷的检出限可分别达到2、0.02、1和0.1 ng,线性范围有两个数量级。离子迁移谱与气相色谱联用,其二维的分离能力可以为复杂混合物的准确定性提供更多的信息,还可以实现不同化合物的选择性检测。     

The potential for clinical applications using a new ionization method combined with ion mobility spectrometry-mass spectrometry

Recently discovered ionization methods for use in mass spectrometry (MS), are widely applicable to biological materials, robust, and easy to automate. Among these, matrix assisted ionization vacuum (MAIV) is astonishing in that ionization of low and high-mass compounds are converted to gas-phase ions with charge states similar to electrospray ionization simply by exposing a matrix:analyte mixture to the vacuum of a mass spectrometer. Using the matrix compound, 3-nitrobenzonitrile, abundant ions are produced at room temperature without the need of high voltage or a laser. Here we discuss chemical analyses advances using MAIV combined with ion mobility spectrometry (IMS) real time separation, high resolution MS, and mass selected and non-mass selected MS/MS providing rapid analyte characterization. Drugs, their metabolites, lipids, peptides, and proteins can be ionized simultaneously from a variety of different biological matrixes such as urine, plasma, whole blood, and tissue. These complex mixtures are best characterized using a separation step, which is obtained nearly instantaneously with IMS, and together with direct ionization and MS or MS/MS provides a fast analysis method that has considerable potential for non-targeted clinical analyses.     

Comprehensive multidimensional separation methods by hyphenation of single-photon ionization time-of-flight mass spectrometry (SPI-TOF-MS) with GC and GC×GC

One- and comprehensive two-dimensional gas chromatography were hyphenated with soft photoionization mass spectrometry. The characteristics of these two- and three-dimensional comprehensive separation techniques are discussed in detail. Using the innovative electron beam pumped excimer light source (EBEL) for single-photon ionization (SPI), organic molecules with ionization energies (E _i ) of below 9.8 eV can be detected by a time-of-flight mass spectrometer (TOF-MS). SPI with 126 nm vacuum ultraviolet (VUV) photons enables the universal and soft ionization of organic molecules. SPI-TOF-MS hyphenated to one-dimensional gas chromatography results in a comprehensive two-dimensional separation method (GC×MS). To demonstrate this, diesel fuel was analyzed, and the resulting GC×MS chromatograms are discussed in depth. A three-dimensional separation method was also realized by combining comprehensive two-dimensional gas chromatography (GC×GC) with SPI-MS. In the resulting separation space, constituents originating from mineral oil diesel blended with biodiesel were dispersed along the two GC separation axes, while the molecular mass axis served as a third separation dimension.     

Ion mobility-mass spectrometry

This review article compares and contrasts various types of ion mobility-mass spectrometers available today and describes their advantages for application to a wide range of analytes. Ion mobility spectrometry (IMS), when coupled with mass spectrometry, offers value-added data not possible from mass spectra alone. Separation of isomers, isobars, and conformers; reduction of chemical noise; and measurement of ion size are possible with the addition of ion mobility cells to mass spectrometers. In addition, structurally similar ions and ions of the same charge state can be separated into families of ions which appear along a unique mass-mobility correlation line. This review describes the four methods of ion mobility separation currently used with mass spectrometry. They are (1) drift-time ion mobility spectrometry (DTIMS), (2) aspiration ion mobility spectrometry (AIMS), (3) differential-mobility spectrometry (DMS) which is also called field-asymmetric waveform ion mobility spectrometry (FAIMS) and (4) traveling-wave ion mobility spectrometry (TWIMS). DTIMS provides the highest IMS resolving power and is the only IMS method which can directly measure collision cross-sections. AIMS is a low resolution mobility separation method but can monitor ions in a continuous manner. DMS and FAIMS offer continuous-ion monitoring capability as well as orthogonal ion mobility separation in which high-separation selectivity can be achieved. TWIMS is a novel method of IMS with a low resolving power but has good sensitivity and is well intergrated into a commercial mass spectrometer. One hundred and sixty references on ion mobility-mass spectrometry (IMMS) are provided.     

Profiling and imaging of tissues by imaging ion mobility-mass spectrometry

Molecular profiling and imaging mass spectrometry (IMS) of tissues can often result in complex spectra that are difficult to interpret without additional information about specific signals. This report describes increasing data dimensionality in IMS by combining two-dimensional separations at each spatial location on the basis of imaging ion mobility-mass spectrometry (IM-MS). Analyte ions are separated on the basis of both ion-neutral collision cross section and m/z, which provides rapid separation of isobaric, but structurally distinct ions. The advantages of imaging using ion mobility prior to MS analysis are demonstrated for profiling of human glioma and selective lipid imaging from rat brain.     

Pharmaceutical metabolite profiling using quadrupole/ion mobility spectrometry/time‐of‐flight mass spectrometry

The use of hybrid quadrupole ion mobility spectrometry time‐of‐flight mass spectrometry (Q/IMS/TOFMS) in the metabolite profiling of leflunomide (LEF) and acetaminophen (APAP) is presented. The IMS drift times (T_d) of the drugs and their metabolites were determined in the IMS/TOFMS experiments and correlated with their exact monoisotopic masses and other in silico generated structural properties, such as connolly molecular area (CMA), connolly solvent‐excluded volume (CSEV), principal moments of inertia along the X, Y and Z Cartesian coordinates (MI‐X, MI‐Y and MI‐Z), inverse mobility and collision cross‐section (CCS). The correlation of T_d with these parameters is presented and discussed. IMS/TOF tandem mass spectrometry experiments (MS² and MS³) were successfully performed on the N‐acetyl‐p‐benzoquinoneimine glutathione (NAPQI‐GSH) adduct derived from the in vitro microsomal metabolism of APAP. As comparison, similar experiments were also performed using hybrid triple quadrupole linear ion trap mass spectrometry (QTRAPMS) and quadrupole time‐of‐flight mass spectrometry (QTOFMS). The abilities to resolve the product ions of the metabolite within the drift tube and fragment the ion mobility resolved product ions in the transfer travelling wave‐enabled stacked ring ion guide (TWIG) demonstrated the potential applicability of the Q/IMS/TOFMS technique in pharmaceutical metabolite profiling. Copyright © 2009 John Wiley & Sons, Ltd.     

Ion mobility-mass spectrometry analysis of isomeric carbohydrate precursor ions

The rapid separation of isomeric precursor ions of oligosaccharides prior to their analysis by mass spectrometry to the nth power (MS ⁿ ) was demonstrated using an ambient pressure ion mobility spectrometer (IMS) interfaced with a quadrupole ion trap. Separations were not limited to specific types of isomers; representative isomers differing solely in the stereochemistry of sugars, in their anomeric configurations, and in their overall branching patterns and linkage positions could be resolved in the millisecond time frame. Physical separation of precursor ions permitted independent mass spectra of individual oligosaccharide isomers to be acquired to at least MS³, the number of stages of dissociation limited only practically by the abundance of specific product ions. IMS–MS ⁿ analysis was particularly valuable in the evaluation of isomeric oligosaccharides that yielded identical sets of product ions in tandem mass spectrometry experiments, revealing pairs of isomers that would otherwise not be known to be present in a mixture if evaluated solely by MS dissociation methods alone. A practical example of IMS–MSⁿ analysis of a set of isomers included within a single high-performance liquid chromatography fraction of oligosaccharides released from bovine submaxillary mucin is described.     

Shift reagents in ion mobility spectrometry: the effect of the number of interaction sites,size and interaction energies on the mobilities of valinol and ethanolamine

Overlapping peaks interfere in ion mobility spectrometry (IMS), but they are separated introducing mobility shift reagents (SR) in the buffer gas forming adducts with different collision cross‐sections (size). IMS separations using SR depend on the ion mobility shifts which are governed by adduct's size and interaction energies (stabilities). Mobility shifts of valinol and ethanolamine ions were measured by electrospray‐ionization ion mobility‐mass spectrometry (MS). Methyl‐chloro propionate (M) was used as SR; 2‐butanol (B) and nitrobenzene (N) were used for comparison. Density functional theory was used for calculations. B produced the smallest mobility shifts because of its small size. M and N have two strong interaction sites (oxygen atoms) and similar molecular mass, and they should produce similar shifts. For both ethanolamine and valinol ions, stabilities were larger for N adducts than those of M. With ethanolamine, M produced a 68% shift, large compared to that using N, 61%, because M has a third weak interaction site on the chlorine atom and, therefore, M has more interaction possibilities than N. This third site overrode the oxygen atoms' interaction energy that favored the adduction of ethanolamine with N over that with M. On the contrary, with valinol mobility shifts were larger with N than with M (21 vs 18%) because interaction energy favored even more adduction of valinol with N than with M; that is, the interaction energy difference between adducts of valinol with M and N was larger than that between those adducts with ethanolamine, and the third M interaction could not override this larger difference. Mobility shifts were explained based on the number of SR's interaction sites, size of ions and SR, and SR–ion interaction energies. This is the first time that the number of interaction sites is used to explain mobility shifts in SR‐assisted IMS. Copyright © 2016 John Wiley & Sons, Ltd.     

Behaviour of tetraalkylammonium ions in high‐field asymmetric waveform ion mobility spectrometry

High‐field asymmetric waveform ion mobility spectrometry (FAIMS) is an ion‐filtering technique recently adapted for use with liquid chromatography/mass spectrometry (LC/MS) to remove interferences during analysis of complex matrices. This is the first systematic study of a series of singly charged tetraalkylammonium ions by FAIMS‐MS. The compensation voltage (CV) is the DC offset of the waveform which permits the ion to emerge from FAIMS and it was determined for each member of the series under various conditions. The electrospray ionization conditions explored included spray voltage, vaporizer temperature, and sheath and auxiliary gas pressure. The FAIMS conditions explored included carrier gas flow rate, electrode temperature and composition of the carrier gas. Optimum desolvation was achieved using sufficient carrier gas (flow rate ≥2 L/min) to ensure stable response. Low‐mass ions (m/z 100–200) are more susceptible to changes in electrode temperature and gas composition than high mass ions (m/z 200–700). As a result of this study, ions are reliably analyzed using standard FAIMS conditions (dispersion voltage ?5000 V, carrier gas flow rate 3 L/min, 50% helium/50%nitrogen, inner electrode temperature 70°C and outer electrode temperature 90°C). Variation of FAIMS conditions may be of great use for the separation of very low mass tetraalkylammonium (TAA) ions from other TAA ions. The FAIMS conditions do not appear to have a major effect on higher mass ions. Copyright © 2010 John Wiley & Sons, Ltd.     

Ion characterisation by comparison of ion mobility spectrometry and mass spectrometry data

The major uncertainty related to ion mobility spectrometry is the lack of knowledge about the characteristics of the ions detected. When using a radioactive atmospheric pressure ionisation source (e.g. ⁶³Ni), from theory proton bound water clusters are expected as reactant ions. When analyte ions occur, proton transfer should lead to proton-bound monomer and dimer ions. To increase the knowledge about those ionisation processes in an ion mobility spectrometer (IMS), a ß-radiation ionisation source was coupled to a mass spectrometer (MS) and an identical one to an IMS. Exemplarily, acetone, limonene and 2- and 5-nonanone were introduced into both instruments in varying concentrations. By correlating the MS and IMS spectra, conclusions about the identities of the ions detected by IMS could be drawn. Proton-bound monomer, dimer and even trimer ions (MH⁺, 2MH⁺, 3MH⁺) could be observed in the MS spectra for acetone and 5-nonanone and could be assigned to the related signals detected by IMS. The oligomers could be expected from theory for increasing concentration. Limonene and 2-nonanone yielded in a variety of different ions and fragments indicating complex gas phase ion chemistry. Those findings on the obviously different behaviour of different analytes require further research focussed on the ion chemistry in IMS including the comparison of different ionisation sources.