An implementable approach to obtain reproducible reduced ion mobility

Ion mobility spectrometry is increasingly in demand for medical applications and its potential for implementation in food quality and safety or process control suggest rising use of instruments in this field as well. All those samples are commonly extremely complex and mostly humid mixtures. Therefore, pre-separation techniques have to be applied. As ion mobility spectrometers with gas-chromatographic pre-separation acquire a huge amount of data, effective data processing and automated evaluation by comparison of detected peak pattern with data bases have to be utilised. This requires accurate on-line calibration of the instruments to guarantee reproducible results, in particular with respect to identification of an analyte by determination of its ion mobility and retention time. To reduce environmental and instrumental influence, the reduced ion mobility is used. It is derived from the drift time normalised to electric field, length of the drift region and to temperature and pressure of the drift gas (traditional method). All data required for this normalisation are afflicted with a particular error and thus leading to a deviation of the calculated ion mobility value. Furthermore, this traditional method enables a calculation of the reduced ion mobility only after the measurement. To avoid those errors and to enable on-line calibration of ion mobility, an instrument specific factor is implemented generally representing all relevant variables. This factor can be determined from an initial measurement of few spectra and can thereafter be applied on the following measurement. The application of this approach obtained reproducible reduced ion mobility values for positive and negative ions over a broad drift time range and for common variation of ambient conditions as well for varying instrument conditions such as electric fields respectively drift times and in different drift gases. Moreover, the reduced ion mobility is available already during the measurements with a significantly higher reliability and accuracy which was increased to a factor of 5 compared to the traditional ion mobility determination and enables an on-line identification of analytes for the first time.     

Buffer gas additives (modifiers/shift reagents) in ion mobility spectrometry: Applications,predictions of mobility shifts,and influence of interaction energy and structure

Ion mobility spectrometry (IMS) is an analytical technique used for fast and sensitive detection of illegal substances in customs and airports, diagnosis of diseases through detection of metabolites in breath, fundamental studies in physics and chemistry, space exploration, and many more applications. Ion mobility spectrometry separates ions in the gas‐phase drifting under an electric field according to their size to charge ratio. Ion mobility spectrometry disadvantages are false positives that delay transportation, compromise patient's health and other negative issues when IMS is used for detection. To prevent false positives, IMS measures the ion mobilities in 2 different conditions, in pure buffer gas or when shift reagents (SRs) are introduced in this gas, providing 2 different characteristic properties of the ion and increasing the chances of right identification. Mobility shifts with the introduction of SRs in the buffer gas are due to clustering of analyte ions with SRs. Effective SRs are polar volatile compounds with free electron pairs with a tendency to form clusters with the analyte ion. Formation of clusters is favored by formation of stable analyte ion‐SR hydrogen bonds, high analytes' proton affinity, and low steric hindrance in the ion charge while stabilization of ion charge by resonance may disfavor it. Inductive effects and the number of adduction sites also affect cluster formation. The prediction of IMS separations of overlapping peaks is important because it simplifies a trial and error procedure. Doping experiments to simplify IMS spectra by changing the ion‐analyte reactions forming the so‐called alternative reactant ions are not considered in this review and techniques other than drift tube IMS are marginally covered.     

Determination of soman and VX degradation products by an aspiration ion mobility spectrometry

An aspiration type ion mobility spectrometry (IMS) has been used to determine chemical warfare agent (CWA) degradation products from liquid samples. This technique is based on ion mobility which depends on the molecular weight, charge and shape. With this method, it is possible to measure the mobility distribution of positive and negative ion clusters simultaneously in six different electrodes. Each measuring electrode determines a different portion of the ion mobility distribution formed within the cell’s radioactive source. The strongest responses for all CWA degradation products and 2-propanol were seen in the order of sixth, fifth and second channels. On the basis of projection calculation, the fingerprints for 2-propanol and soman (GD; pinacolyl methylphosphonofluoridate) and VX o-ethyl-S-[2(diisopropylamino)ethyl] methylphosphonothioate) degradation products can be separated from each other. The detection levels for ethyl methylphosphonate (EMPA), pinacolyl methylphosphonate (PMPA), and ethylphosphonic acid (EPA) were 37.2 (37.2 μg/ml), 54.1 (54.1 μg/ml) and 55.1 ppm (55.1 μg/ml), respectively. However, the separation efficiency between different CWA degradation products was quite poor. The projections of these compounds were between 0.9976 and 0.9989, and this means that these fingerprints were identical. Thus, it is only possible to get one profile for all these degradation products of soman and VX. The data provided show that IMS is suitable as a simple technique for screening of CWA degradation products.     

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.     

Caffeine and glucosamine mobility shifts by adduction with 2‐butanol depended on interaction energy,charge delocalization,and steric hindrance in ion mobility spectrometry

Ion mobility spectrometry (IMS) is an analytical technique that separates gas‐phase ions drifting under an electric field according to their size to charge ratio. We used electrospray ionization‐drift tube IMS coupled to quadrupole mass spectrometry to measure the mobilities of glucosamine (GH⁺) and caffeine (CH⁺) ions in pure nitrogen or when the shift reagent (SR) 2‐butanol was introduced in the drift gas at 6.9 mmol m⁻³. Binding energies of 2‐butanol‐ion adducts were calculated using Gaussian 09 at the CAMB3LYP/6‐311++G(d,p) level of theory. The mobility shifts with the introduction of 2‐butanol in the drift gas were −2.4% (GH⁺) and −1.7% (CH⁺) and were due to clustering of GH⁺ and CH⁺ with 2‐butanol. The formation of GBH⁺ was favored over that of CBH⁺ because GBH⁺ formed more stable hydrogen bonds (83.3 kJ/mol) than CBH⁺ (81.7 kJ/mol) for the reason that the positive charge on CH⁺ is less sterically available than on GH⁺ and the charge is stabilized by resonance in CH⁺. These results are a confirmation of the arguments used to explain the drift behavior of these ions when ethyl lactate SR was used (Bull Kor Chem Soc 2014, 1023–1028). This study is a step forward to predict IMS separations of overlapping peaks in IMS spectra, simplifying a procedure that is trial and error by now.     

一种微型FAIMS传感器芯片的研制

基于微机电系统(MEMS)技术,研制了一种微型高场非对称波形离子迁移谱(FAIMS)传感器芯片.芯片尺寸为18.8mm×12.4mm×1.2mm,由离子化区、迁移区、离子检测区组成.采用真空紫外灯离子源在大气压环境下对样品进行离子化,经过离子化区中聚焦电极的电场作用,实现离子在进入迁移区之前的聚焦,提高离子信号的强度.通过在上下玻璃上溅射Au/Cr(300nm/30nm)金属,并与厚度为200μm、采用感应耦合等离子体(ICP)工艺刻蚀的硅片键合,形成迁移区的矩形通道,尺寸为10mm×5mm×0.2mm.离子检测区为三排直径200μm、间距100μm交错排列的圆柱阵列式微法拉第筒,能同时检测正负离子.采用频率为2MHz,最大电压为364V,占空比为30%的高场非对称方波电压进行FAIMS芯片实验.以丙酮和甲苯为实验样品,载气流速80L·h-1,补偿电压从-10V到3V以0.1V的步长进行扫描,得到了丙酮和甲苯的FAIMS谱图,验证了FAIMS芯片的性能.丙酮和甲苯的FAIMS-MS实验进一步表明FAIMS系统实现了离子分离和过滤功能.     

The effect of humidity on sensitivity of amine detection in ion mobility spectrometry

Vaporized water molecules are unavoidably present in every ion mobility spectrometry (IMS) measurement. In general, this humidity is seen in positive mode IMS-spectra as protonated water clusters producing reactant ions. Clusters containing water molecules are also abundant among ions generated by an analyte. In this paper the influence of humidity on IMS-spectra was systematically investigated and determined by measuring different concentrations of a selected amine at various levels of humidity. The selected amine, trimethylamine (TMA), was chosen as the model analyte due to its atmospheric importance. During the measurements, surplus water vapor was introduced into the drift section inside the IMS instrument; the concentrations of both amine and water were adjusted by controlling the gas flows. The simultaneous presence of water vapor and analyte at various predefined concentrations revealed the sensitivity of the IMS-technique to water and the effect of moisture on the ion mobility distribution. The results indicated that the existence, positions and shapes of the peaks are strongly dependent on the amount of moisture. However, the sensitivity of detection is weakly dependent on humidity if this detection is based on monomer ion peak or the sum of peaks generated by the analyte, In addition, the main principles of the adjustment of sample and water concentrations are presented here.     

Exploring and modeling the ion mobility spectrometry of perindopril: Example of protonation-dissociation reactions in large molecules

The current research is constructed for considering the chemical ionization and dissociation of perindopril in the positive mode of corona discharge ion mobility spectrometry. Four product ion peaks are observed in the ion mobility spectrum of perindopril erbumine at the cell temperature of 473 K. These peaks are assigned through the obtained intensity variation analysis in the ion mobility spectra over the elapsed time accompanied by the calculations backed by the validated density functional theory (DFT). In this regard, the most stable ionic species associated with each peak and the corresponding reliable generation pathways are found by the well-confirmed meta hybrid density functional method, M06-2X. The peaks are assigned to the protonated perindopril and its dissociation products, including counter ion and the related fragment ions. However, the structures of the neutral perindopril in the gas phase are thoroughly assessed to find a more stable one. The predicted chemical ionization products by the theory are in excellent agreement with our presented experiment here. Theoretical evaluations demonstrated that the production of a fragment by dissociation process occurs when perindopril gets a proton from the ionization region. Also, without protons, there is no dissociation process. Therefore, our mechanism investigated here is the proton transfer one. All possible sites of perindopril are considered theoretically for protonation along with their possible reactions. In addition to the computed PES, the assigned ions for obtained spectra are confirmed by the computed equilibrium constants and rate constants. Our theoretical results show that the peak of the main fragment is for M-CH₃CH₂OH produced by a reaction pathway involving no barrier. This study opens new perspectives in interpreting large molecules spectra for future studies.     

Baseline resolution of isomers by traveling wave ion mobility mass spectrometry: investigating the eff ects of polarizable drift gases and ionic charge distribution

We have studied the behavior of isomers and analogues by traveling wave ion mobility mass spectrometry (TWIM‐MS) using drift‐gases with varying masses and polarizabilities. Despite the reduced length of the cell (18 cm), a pair of constitutional isomers, N‐butylaniline and para‐butylaniline, with theoretical collision cross‐section values in helium (Ω_He) differing by as little as 1.2 Ų (1.5%) but possessing contrasting charge distribution, showed baseline peak‐to‐peak resolution (R_p‐p) for their protonated molecules, using carbon dioxide (CO₂), nitrous oxide (N₂O) and ethene (C₂H₄) as the TWIM drift‐gas. Near baseline R_p‐p was also obtained in CO₂ for a group of protonated haloanilines (para‐chloroaniline, para‐bromoaniline and para‐iodoaniline) which display contrasting masses and theoretical Ω_He, which differ by as much as 15.7 Ų (19.5%) but similar charge distributions. The deprotonated isomeric pair of trans‐oleic acid and cis‐oleic acid possessing nearly identical theoretical Ω_He and Ω_N2 as well as similar charge distributions, remained unresolved. Interestingly, an inversion of drift‐times were observed for the 1,3‐dialkylimidazolium ions when comparing He, N₂ and N₂O. Using density functional theory as a means of examining the ions electronic structure, and He and N₂‐based trajectory method algorithm, we discuss the effect of the long‐range charge induced dipole attractive and short‐range Van der Waals forces involved in the TWIM separation in drift‐gases of differing polarizabilities. We therefore propose that examining the electronic structure of the ions under investigation may potentially indicate whether the use of more polarizable drift‐gases could improve separation and the overall success of TWIM‐MS analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Travelling‐wave ion mobility and negative ion fragmentation of high‐mannose N‐glycans

The isomeric structure of high‐mannose N‐glycans can significantly impact biological recognition events. Here, the utility of travelling‐wave ion mobility mass spectrometry for isomer separation of high‐mannose N‐glycans is investigated. Negative ion fragmentation using collision‐induced dissociation gave more informative spectra than positive ion spectra with mass‐different fragment ions characterizing many of the isomers. Isomer separation by ion mobility in both ionization modes was generally limited, with the arrival time distributions (ATD) often showing little sign of isomers. However, isomers could be partially resolved by plotting extracted fragment ATDs of the diagnostic fragment ions from the negative ion spectra, and the fragmentation spectra of the isomers could be extracted by using ions from limited areas of the ATD peak. In some cases, asymmetric ATDs were observed, but no isomers could be detected by fragmentation. In these cases, it was assumed that conformers or anomers were being separated. Collision cross sections of the isomers in positive and negative fragmentation mode were estimated from travelling‐wave ion mobility mass spectrometry data using dextran glycans as calibrant. More complete collision cross section data were achieved in negative ion mode by utilizing the diagnostic fragment ions. Examples of isomer separations are shown for N‐glycans released from the well‐characterized glycoproteins chicken ovalbumin, porcine thyroglobulin and gp120 from the human immunodeficiency virus. In addition to the cross‐sectional data, details of the negative ion collision‐induced dissociation spectra of all resolved isomers are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Real-time monitoring traces of SF6 in near-source ambient air by ion mobility spectrometry

The leakage of sulphur hexafluoride (SF₆) gas threats the global climate changes and personnel safety. Monitoring the concentration of SF₆ in its application places is an industry regulation. In this study, ion mobility spectrometry (IMS) was developed for fast monitoring traces of SF₆ in near-source ambient air. Due to the water is an important part of the natural air and affects most atmospheric measurements, the operating parameters of IMS monitoring SF₆ were optimised for quantitative analysis of SF₆ at different relative humidity (RH). It is discovered two main product ions SF₆^? and SOF₄^? by IMS at different RH. The calibration curves of SF₆ were investigated by its relationship with the peak intensity of SOF₄^– for real application. The time resolution of the measurement was obtained less than 1 s and the limit of detection (LOD) achieved 0.16–0.68 ppm with a data averaging of 30 times. At last, the simulated application of monitoring SF₆ leakage was tested in the fume hood of our lab. The results showed a great potential application prospect of IMS in monitoring SF₆ in the ambient air of its application places.     

A comparative study of CH4 and CF4 rf discharges using a consistent plasma physics and chemistry simulator

A self-consistent, one-dimensional simulator for the physics and chemistry of radio frequency (rf) plasmas was developed and applied for CH₄ and CF₄. The simulator consists of a fluid model for the discharge physics, a commercial Boltzmann equation solver for calculations of electron energy distribution fuction (EEDF), a generalized plasma chemistry code, and an interface module among the three models. The CH₄ and CF₄ discharges are compared and contrasted: CH₄ plasmas are electropositive, with negative ion densities one order of magnitude less than those of electrons, whereas CF₄ plasmas are electronegative, with ten times more negative ions than electrons. The high-energy tail of tire EEDF in CH₄, lies below both the Druyvensteyn and Maxwell distributions, whereas tire EEDF high-energy tail in CF₄ lies between the two. For CH₄, the chemistry model was applied for four species, namely, CH₄ CH₃ CH₂, and H, whereas for CF₄, five species were examined namely CF₄, CF₃, CF₂, CF, and F The predicted densities and profiles compare favorably with experimental data. Finally, the chemistry results were fedback into the physics model until convergence was obtained.     

Structural Elucidation of β‐Lactam Diastereoisomers through Ion Mobility Mass Spectrometry Studies and Theoretical Calculations

The ion mobility combined with mass spectrometry and theoretical calculations were used to characterize and separate six diastereoisomeric β‐lactams. The influence of traveling wave height and wave velocity, size of the alkali metal ion (Li⁺, Na⁺ and K⁺) and drift gases with varying masses and polarizabilities (N₂ and CO₂) on separation efficacy was additionally examined. The best separation of diastereoisomers of β‐lactams was observed for adducts with Na⁺ and Li⁺ ions, whereas other parameters had little impact on separation process. The isomeric β‐lactams were characterized by both experimental and theoretical collision cross sections. The theoretically calculated values of collision cross sections obtained from extensive molecular dynamics and density functional theory calculations for model structures agreed well with those established experimentally. The relationship between separation efficacy and the configuration at the carbon atoms C5 and C6 of β‐lactam ring was defined. Copyright © 2016 John Wiley & Sons, Ltd.     

Fast detection of methyl tert-butyl ether from water using solid phase microextraction and ion mobility spectrometry

Methyl tert-butyl ether (MTBE) is commonly used as chemical additive to increase oxygen content and octane rating of reformulated gasoline. Despite its impact on enhancing cleaner combustion of gasoline, MTBE poses a threat to surface and ground water when gasoline is released into the environment. Methods for onsite analysis of MTBE in water samples are also needed. A less common technique for MTBE detection from water is ion mobility spectrometry (IMS). We describe a method for fast sampling and screening of MTBE from water by solid phase microextraction (SPME) and IMS. MTBE is adsorbed from the head space of a sample to the coating of SPME fiber. The interface containing a heated sample chamber, which couples SPME and IMS, was constructed and the SPME fiber was introduced into the sample chamber for thermal desorption and IMS detection of MTBE vapors. The demonstrated SPME-IMS method proved to be a straightforward method for the detection of trace quantities of MTBE from waters including surface and ground water. We determined the relative standard deviation of 8.3% and detection limit of 5 mg L⁻¹ for MTBE. Because of short sampling, desorption, and detection times, the described configuration of combined SPME and IMS is a feasible method for the detection of hazardous substances from environmental matrices.     

Analysis of a stacked-triangular platinum carbonyl cluster dianion, [Pt3(CO)6] 3 2− by252Cf-Plasma Desorption Mass Spectrometry

²⁵²Cf-Plasma Desorption Mass Spectrometry (²⁵²Cf-PDMS) has been used to investigate the [(Ph₃PCH₂C₅H₄)Fe(C₅H₅)]⁺ salt of the prototype dianionic, platinum carbonyl cluster, [Pt₃(CO)₃(₂-CO)₃] ₃ ^2– . An envelope of singly charged [Pt₉(CO) _x ]^– ions with the principal peak centered atx=8 was observed in the negative ion mass spectrum as a result of successive losses of the carbonyl ligands from the intact platinum core. Another feature of the negative ion spectrum was the prominent occurrence of other envelopes of multiple peaks which conform to Pt₁₂, Pt₁₅, Pt₁₈, Pt₂₁, and Pt₂₄ singly charged metal cores. An unexpected observation was the presence of singly charged positive ions of the dianionic cluster which were formed without incorporation of the counterion. A similar but, largely unresolvable, broad envelope of singly charged ions containing the Pt₉ core resulted with a peak maximum corresponding closely to the completely carbonylated cluster. The peak distribution extended from the fully decarbonylated cluster to well beyond the mass of the fully carbonylated cluster. Analogous peaks attributable to singly charged positive ions of the Pt₁₂, Pt₁₅, and Pt₁₈ clusters were also evident. Very little fragmentation was observed below the molecular ion in either the positive or negative ion mass spectra except for ions associated with the counterion. A detailed analysis of the mass spectra, including the types of ions observed and correlations with the molecular architecture are described.     

Sr2MgSiO5∶Ce3+的发光性质研究

报道了Sr2MgSiO5∶Ce3+荧光粉的发光性质.     

Evaporation of ionic liquids at atmospheric pressure: study by ion mobility spectrometry

A conventional ion mobility spectrometry (IMS) was used to study atmospheric pressure evaporation of seven pure imidazolium and pyrrolidinium ionic liquids (ILs) with [Tf₂N], [PF₆], [BF₄] and [fap] anions. The positive drift time spectra of the as-received samples measured at 220 °C exhibited close similarity; the peak at reduced mobility K₀ = 1.99 cm² V⁻¹ s⁻¹ was a dominant spectral pattern of imidazolium-based ILs. With an assumption that ILs vapor consists mainly of neutral ion pairs, which generate the parent cations in the reactant section of the detector, and using the reference data on the electrical mobility of ILs cations and clusters, this peak was attributed to the parent cation [emim]. Despite visible change in color of the majority of ILs after the heating at 220 °C for 5 h, essential distinctions between spectra of the as-received and heated samples were not observed. In negative mode, pronounced peaks were registered only for ILs with [fap] anion.     

Diagnostic filtering to screen polycyclic polyprenylated acylphloroglucinols from Garcinia oblongifolia by ultrahigh performance liquid chromatography coupled with ion mobility quadrupole time-of-flight mass spectrometry

A novel multistage MS approach, insource collision-induced dissociation (CID) combined with Time Aligned Parallel (TAP) fragmentation, was established to study the fragmentation behavior of polycyclic polyprenylated acylphloroglucinols (PPAPs), which could provide a more reliable fragmentation relationship between precursor and daughter ions. The diagnostic ions for different subtypes of PPAPs and their fragmentation behaviors have been summarized. Moreover, a new and reliable multidimensional analytical workflow that combines ultrahigh performance liquid chromatography (UHPLC), data-independent mass spectrometry (MS^E), and tandem MS with ion mobility (IM) has been optimized and established for the analysis of PPAPs in the plant Garcinia oblongifolia by diagnostic filtering. Diagnostic fragment ions were used to selectively screen PPAPs from extracts, whereas IM coupled to MS was used to maximize the peak capacity. Under the optimized UHPLC-IM-MS^E and UHPLC-IM-MS/MS method, 140 PPAPs were detected from the crude extract of G. oblongifolia, and 10 of them were unambiguously identified by comparing them to the reference compounds. Among those PPAPs, 7 pairs of coeluting isobaric PPAPs that were indistinguishable by conventional UHPLC-HRMS alone, were further resolved using UHPLC-IM-MS. It is anticipated that the proposed method will be extended to the rapid screening and characterization of the other targeted or untargeted compounds, especially these coeluting isomers in complex samples.     

KZnF3∶Ce，Tb的溶剂热合成及光谱性质

采用溶剂热法合成了Ce3+,Tb3+单掺和双掺KZnF3发光粉。分析了样品的结构与形貌。结果表明,所合成的样品均为单相,颗粒粒度分布均匀。讨论了它们的光谱特性。研究发现,在KZnF3∶Ce3+激发光谱中激发带劈裂成2个带峰,最大发光中心分别位于263 nm(主峰)和246 nm,而在发射光谱中只观察到1个带状发射峰,最大发射中心位于330 nm。在KZnF3∶Tb3+激发光谱中存在较强的基质激发峰,而在发射光谱中,发现Tb3+的5D4→7FJ(J=6,5,4,3)跃迁。在KZnF3双掺体系中,Tb3+的发光强度随Ce3+的浓度增加而增强,存在Ce3+→Tb3+能量传递,尤其是Tb3+的5D4→7F5跃迁发射显著增强,有望成为一种有发展前途的绿色荧光材料。     

Al NMR studies of Ce-Al mixed oxides: origin of 40 ppm peak

CeO₂-γ-Al₂O₃ mixed oxides have been prepared by using both co-precipitation and impregnation methods followed by calcination at 650°C and investigated by ²⁷Al MAS NMR, powder X-ray diffraction and temperature programmed reduction techniques to understand the nature of chemical interaction existing between CeO₂ and γ-Al₂O₃. The ²⁷Al NMR spectra of CeO₂-containing samples showed an additional peak placed at 40 ppm along with the two peaks at 68 and 6 ppm which originate from the tetrahedrally and octahedrally coordinated Al³⁺ ions present in γ-Al₂O₃. As the concentration of CeO₂ in the mixed oxide increased, the intensity of the 40 ppm peak increased and this was the prominent peak for CeO₂-rich mixed oxide samples. The origin of this 40 ppm peak is discussed and it is inferred that this peak is due to Al³⁺ ions, which are present in CeO₂ lattice, forming a solid solution.