Separation of Ions from Volatile Organic Compounds Using High-Field Asymmetric Waveform Ion Mobility Spectrometry-Mass Spectrometer

A combination of high-field asymmetric waveform ion mobility spectrometry （FAIMS） with mass spectrometer （MS） was analyzed. FAIMS separates ions from the volatile organic compounds in the gas-phase as an ion-filter for MS. The sample ions were created at ambient pressure by ion source, which was equipped with a 10.6 eV UV discharge lamp （A=116.5 nm）. The drift tube of FAIMS is composed of two parallel planar electrodes and the dimension is 10 mm×8 mm×0.5 mm. FAIMS was investigated when driven by the high-filed rectangular asymmetric waveform with the peak-to-peak voltage of 1.36 kV at the frequency of 1 MHz and the duty cycle of 30%. The acetone, the butanone, and their mixture were adopted to characterize the FAIMS-MS. The mass spectra obtained from MS illustrate that there are ion-molecular reactions between the ions and the sample neutral molecular. And the proton transfer behavior in the mixture of the acetone and the butanone is also observed. With the compensation voltage tuned from -30 V to 10 V with a step size of 0.1 V, the ion pre-separation before MS is realized.

Electron Attachment Studies for CHCl3 Using Ion Mobility Spectrometry

The dissociative electron attachment process for CHCl3 at different electric field have been studied with nitrogen as drift and carrier gas using corona discharge ionization source ion mobility spectrometry （CD-IMS）. The corresponding electron attachment rate constants varied from 1.26×10-8 cm3/（molecules s） to 8.24×10-9 cm3/（molecules s） as the electric field changed from 200 V/cm to 500 V/cm. At a fixed electric field in the drift region, the attachment rate constants are also detected at different sample concentration. The ionmolecule reaction rate constants for the further reaction between Cl^- and CHCl3 are also detected, which indicates that the technique maybe becomes a new method to research the rate constants between ions and neural molecules. And the reaction rate constants between Cl- and CHCl3 are the first time detected using CD-IMS.

Peak Profile Analysis in High Field Asymmetric Wave Ion Mobility Spectrometry

High field asymmetric wave ion mobility spectrometry （FAIMS） is a powerful tool to detect and characterize gas-phase ions, while the unsolvable partial differential equation of ions moving in ion drift tube poses a big challenge to FAIMS spectral peak analysis. In this work, a universal and effective model of FAIMS spectral peak profile has been proposed by introducing ion trajectory and loss height. With this model, the influence of the structure of ion drift tube, dispersion voltages, compensation voltages, and carrier gas flow rate on the FAIMS spectral peak characteristics like peak shape, full width at half maximum and peak height is analyzed and discussed. The results show that the influence of different factors on the FAIMS spectral peak profile can be qualitatively described by the model which agrees with the experimental data.

Determination of alcohol compounds using corona discharge ion mobility spectrometry

Ion mobility spectrometry （IMS） is a very fast, highly sensitive, and inexpensive technique, it permits efficient monitoring of volatile organic compounds like alcohols. In this article, positive ion mobility spectra for six alcohol organic compounds have been systematically studied for the first time using a high-resolution IMS apparatus equipped with a discharge ionization source. Utilizing protonated water cluster ions （H2O）nH^＋ as the reactant ions and clean air as the drift gas, alcohol organic compounds, ethanol, 1- propanol, 2-propanol, 1-butanol, 1-pentanol and 2-octanol, all exhibit product ion characteristic peaks in their respective ion mobility spectrometry, that is a result of proton transfer reactions between the alcohols and reaction ions （H2O）nH^＋. The mixture of these alcohols, including two isomers, has been detected, and the results showed that they could be distinguished effectively in the ion mobility spectrum. The reduced mobility values have been determined, which are in very well agreement with the traditional ^63Ni-IMS experimental values. The exponential dilution method was used to calibrate the alcohol concentrations, and a detection limit available for the alcohols is in order of magnitude of a few ng/L.

Rapid authentication of sesame oil using ion mobility spectrometry and chemometrics

To ensure authenticity of sesame oil,an authentication technology was proposed using ion mobility spectrometry(IMS)and chemometrics.One-class classification(OCC)methods including one-class partial least squares(OCPLS)and one-class support vector machine(OCSVM)were employed to build authentication models for sesame oil.Subsequently,an independent test set was used to validate the constructed models.Validation set of 45 adulterated oils indicated that prediction correction rate of OCPLS model reached 95.6%(43 out of 45).Moreover,the complete set of sesame oils adulterated by sesame oil essence could be identified as counterfeit.Compared with previous studies,OCPLS model could work to identify untargeted adulteration.In conclusion,OCC method could effectively detect adulterated sesame oils containing as little as 10%other vegetable oils.This study provided a rapid screening method for adulterated sesame oil in market surveillance and a reference for developing authentication methods of other edible oils.

Breath-by-breath measurement of exhaled ammonia by acetonemodifier positive photoionization ion mobility spectrometry via online dilution and purging sampling

Exhaled ammonia(NH_(3))is an essential noninvasive biomarker for disease diagnosis.In this study,an acetone-modifier positive photoionization ion mobility spectrometry(AM-PIMS)method was developed for accurate qualitative and quantitative analysis of exhaled NH_(3)with high selectivity and sensitivity.Acetone was introduced into the drift tube along with the drift gas as a modifier,and the characteristic NH_(3)product ion peak of(C_(3)H_(6)O)_(4)NH_(4)^(+)(K_(0)=1.45 cm^(2)/V·s)was obtained through the ion-molecule reaction with acetone reactant ions(C_(3)H_(6)O)_(2)H^(+)(K_(0)=1.87 cm^(2)/V·s),which significantly increased the peak-to-peak resolution and improved the accuracy of exhaled NH_(3)qualitative identification.Moreover,the interference of high humidity and the memory effect of NH_(3)molecules were significantly reduced via online dilution and purging sampling,thus realizing breath-by-breath measurement.As a result,a wide quantitative range of 5.87-140.92μmol/L with a response time of 40 ms was achieved,and the exhaled NH_(3)profile could be synchronized with the concentration curve of exhaled CO_(2).Finally,the analytical capacity of AM-PIMS was demonstrated by measuring the exhaled NH_(3)of healthy subjects,demonstrating its great potential for clinical disease diagnosis.

Measurement of Ion Mobilities of Selected Amines by Ion Mobility Spectrometry

The ion mobilities of selected amines were measured by IMS. The minimum detection limits and linear ranges of selected amines were detected.

MALDI coupled with laser-postionization and trapped ion mobility spectrometry contribute to the enhanced detection of lipids in cancer cell spheroids

Cancer cell spheroids(CCS) are a valuable three-dimensional cell model in cancer studies because they could replicate numerous characteristics of solid tumors. Increasing researches have used matrix-assisted laser desorption/ionization mass spectrometry imaging(MALDI-MSI) to investigate the spatial distribution of endogenous compounds(e.g., lipids) in CCS. However, only limited lipid species can be detected owing to a low ion yield by using MALDI. Besides, it is still challenging to fully characterize the structural diversity of lipids due to the existence of isomeric/isobaric species. Here, we carried out the initial application of MALDI coupled with laser-postionization(MALDI-2) and trapped ion mobility spectrometry(TIMS) imaging in HCT116 colon CCS to address these challenges. We demonstrated that MALDI-2 is capable of detecting more number and classes of lipids in HCT116 colon CCS with higher signal intensities than MALDI. TIMS could successfully separate numerous isobaric/isomeric species of lipids in CCS. Interestingly, we found that some isomeric/isobaric species have totally different spatial distributions in colon CCS. Further MS/MS imaging analysis was employed to determine the compositions of fatty acid chains for isomeric species by examining disparities in signal intensities and spatial distributions of product ions. This work stresses the robust ability of TIMS and MALDI-2 imaging in analyzing endogenous lipids in CCS, which could potentially become powerful tools for future cancer studies.

Dimension-Enhanced Ultra-High Performance Liquid Chromatography/Ion Mobility-Quadrupole Time-of-Flight Mass Spectrometry Combined with Intelligent Peak Annotation for the Rapid Characterization of the Multiple Components from Seeds of Descurainia sophia

The complex composition of herbal metabolites necessitates the development of powerful analytical techniques aimed to identify the bioactive components.The seeds of Descurainia sophia(SDS)are utilized in China as a cough and asthma relieving agent.Herein,a dimension-enhanced integral approach,by combining ultra-high performance liquid chromatography/ion mobility-quadrupole time-of-flight mass spectrometry(UHPLC/IMQTOF-MS)and intelligent peak annotation,was developed to rapidly characterize the multicomponents from SDS.Good chromatographic separation was achieved within 38 min on a UPLC CSH C18(2.1×100 mm,1.7μm)column which was eluted by 0.1%formic acid in water(water phase)and acetonitrile(organic phase).Collision-induced dissociation-MS^(2)data were acquired by the data-independent high-definition MS^(E)(HDMS^(E))in both the negative and positive electrospray ionization modes.A major components knockout strategy was applied to improve the characterization of those minor ingredients by enhancing the injection volume.Moreover,a self-built chemistry library was established,which could be matched by the UNIFI software enabling automatic peak annotation of the obtained HDMS^(E)data.As a result of applying the intelligent peak annotation workflows and further confirmation process,a total of 53 compounds were identified or tentatively characterized from the SDS,including 29 flavonoids,one uridine derivative,four glucosides,one lignin,one phenolic compound,and 17 others.Notably,four-dimensional information related to the structure(e.g.,retention time,collision cross section,MS^(1)and MS^(2)data)was obtained for each component by the developed integral approach,and the results would greatly benefit the quality control of SDS.

Structures of Stoichiometric Sodium Oxide Cluster Cations Studied by Ion Mobility Mass Spectrometry

Structures of stable compositions of sodium oxide cluster cations (NanOm+,n≤11) have been investigated by ion mobility mass spectrometry. Stoichiometric compositions series, Na(Na2O)(n-1)/2^+(n=3, 5, 7, 9, and 11), were observed as stable composition series, and NaO(Na2O)(n-1)/2^+ series (n=5, 7, 9, and 11) were observed as secondary stable series in the mass spectra. To assign the structures of these cluster ion series, collision cross sections between the ions and helium buffer gas were determined experimentally from the ion mobility measurements. Theoretical collision cross sections were also calculated for optimized structures of these compositions. Finally, the structures of Na(Na2O)(n-1)/2^+ and NaO(Na2O)(n-1)/2^+ were assigned to those having similar structural frames for each n except for n=9. All bonds in the assigned structures of Na(Na2O)(n-1)/2^+ were between sodium and oxygen. On the other hand, there was one O-O bond in addition to Na-O bonds in NaO(Na2O)(n-1)/2^+. This result indicates that NaO(Na2O)(n-1)/2^+ have a peroxide ion (O22-) as a substitute for an oxide ion (O2-) of Na(Na2O)(n-1)/2^+. As a result, both stable series, Na(Na2O)(n-1)/2^+ and NaO(Na2O)(n-1)/2^+, are closed-shell compositions. These closed-shell characteristics have a strong influence on the stability of sodium oxide cluster cations.

Molecular Structural Characterization and Quantitative Prediction of Reduced Ion Mobility Constants for Diversified Organic Compounds

Based on two-dimensional topological structures, a novel molecular electronegativity interaction vector with hybridization （MEHIV） was developed to describe atomic hybridization state in different molecular environments. Five quantitative models by MEHIV characterization and multiple linear regression modeling were successfully established to predict reduced ion mobility constants （Ko） of alkanes, aromatic hydrocarbons, fatty alcohols, fatty aldehydes and ketones and carboxylic esters. The correlation coefficients Roy by leave-one-out cross-validation are 0.792, 0.787, 0,949, 0.972 and 0.981, respectively, and the standard deviations SDcv are 0.067, 0.086, 0.064, 0.043 and 0.042, respectively. These results suggested that MEHIV is an excellent topological index descriptor with many advantages such as straightforward physicochemical meaning, high characterization competence, convenient expansibility and easy manipulation.

基于离子淌度质谱技术的离子光谱研究进展

离子光谱结合了质谱的高灵敏度和光谱的分子结构特异性的优势,可对蛋白质、多肽、糖类、寡核苷酸等复杂体系进行结构表征和鉴定。但当存在同分异构体时,离子光谱难以从叠加的谱图中得到单个异构体的光谱信息。离子淌度质谱技术可通过区分待测离子质荷比和分子空间尺寸差异来实现异构体的分离。离子淌度可以对异构体分离后分别引入到后续的光谱和质谱分析中,减少了由异构体引起的光谱叠加问题,光谱可以进一步验证离子淌度的分离效果,因此质谱、光谱、离子淌度谱的有机结合在得到异构体精确光谱的同时,也为离子淌度质谱分析带来了新的维度和深度。本文概述了近20年来基于各类离子淌度质谱技术的光谱仪器发展和应用情况,总结目前存在的问题,并展望多维度结构质谱的新需求。

Rapid Profiling and Characterization of the Multicomponents from the Root and Rhizome of Salvia miltiorrhiza by Ultra-High Performance Liquid Chromatography/Ion Mobility-Quadrupole Time-of-Flight Mass Spectrometry in Combination with Computational Peak Annotation Workflows

Herbal components characterization represents a challenging task because of the co-existing of multiple classes of naturally occurring compounds with wide spans of polarity,molecular mass,and the ubiquitous isomerism.The root and rhizome of Salvia miltiorrhiza have been utilized as a reputable traditional Chinese medicine Salviae Miltiorrhizae Radix et Rhizoma(Dan-Shen)in the treatment of cardiovascular disease.Herein,a dimensionenhanced ultra-high performance liquid chromatography/ion mobility/quadrupole time-of-flight mass spectrometry approach in combination with intelligent peak annotation workflows was established aimed to rapidly characterize the multicomponents from S.miltiorrhiza.Due to the sufficient optimization,satisfactory chromatography separation was enabled on an HSS T3 column within 33 min using 0.1%formic acid in water(A)and acetonitrile(B)as the mobile phase,while the data-independent HDMS^(E) in both the negative and positive electrospray ionization modes was utilized for the high-coverage MS^(2) data acquisition.Streamlined automatic peak annotation by searching an in-house library(recording 198 known compounds)followed by the subsequent confirming steps(e.g.,comparison with the reference compounds,fragmentation pathways analysis,and retention behavior comparison,etc.),allowed us to identify or tentatively characterize a total of 86 components(including 50 terpenoids,21 phenolic acids,and 15 others)from S.miltiorrhiza.Importantly,three-dimensional structure information,such as the retention time,MS^(1) and MS^(2) data,and collision cross section(CCS),was provided,which can facilitate the more reliable characterization of herbal components.

Ultra-High Performance Liquid Chromatography/Ion Mobility-Quadrupole Time-of-Flight Mass Spectrometry and Database-Driven Automatic Peak Annotation for the Rapid Profiling and Characterization of the Multicomponents from Stephaniae Tetrandrae Radix(Fang-Ji)

Objective:Quality control of traditional Chinese medicine(TCM)begins with the chemical basis elucidation.The root of Stephania tetrandra has long been utilized as an antirheumatic,analgesic,and diuretic TCM,Stephaniae Tetrandrae Radix(STR;Fang-Ji).Powerful analytical strategies enabling its multicomponent characterization is still rare.Methods:A rapid,reliable,and enhanced profiling approach,by ultra-high performance liquid chromatography coupled with ion mobility/quadrupole time-of-flight mass spectrometry(UHPLC/IM-QTOF-MS)and automatic peak annotation facilitated by computational matching of in-house library,was established and utilized to characterize the multicomponents from STR.A knockout strategy was utilized by automated valve switching to overcome the interference of predominant peaks.Results:Good chromatographic separation was achieved within 17 min on a reversed-phase BEH C18 column eluted with acetonitrile/0.1%ammonium hydroxide in water,while data-independent high-definition MS^(E)(HDMS^(E))in positive mode was applied to acquire the MS^(2)data by using a Vion TM IM-QTOF instrument,which in theory,could cover all the profiled precursor ions.An in-house library of 163 compounds was established and incorporated into the UNIFITM platform.By feat of these efforts,we were able to identify or tentatively characterize 76 alkaloids from the methanolic extract of STR,including 14 aporphine-type,four morphine-type,48 bisbenzylisoquinoline-type,seven tetrahydroprotoberberine-type,one protopine-type,one benzylisoquinoline-type,and one other.Four-dimensional information,such as the retention time,collision cross section(CCS),high-accuracy MS1 and MS2 data,for each component was provided.Conclusions:The systematic multicomponent characterization of STR was accomplished with high coverage,high degree of automation,and high reliability.