新型三角形电极圆环离子阱的理论模拟研究

圆环离子阱由于其离子储存能力明显优于相同体积下的三维离子阱,近年来被认为是离子阱小型化发展的另一个重要方向。为进一步优化圆环形离子阱的质谱性能,特别是质量分辨能力,本研究提出了一种由三角形电极构建的新型圆环离子阱,它由两个完全等同的、截面为三角形的圆环电极及两个大小不等的圆筒型电极所组成,离子通过共振激发方式弹出。通过理论模拟和对电极结构的优化,获得了具有非对称性的三角形电极结构,通过改善圆环结构,优化电场分布,提高了离子引出效率和离子阱的质量分辨能力,其中一种最优化结构的圆环离子阱对m/z 609离子的质量分辨率达到1486。     

Development of a SIMION-Simulated Ion Funnel Tube for Proton Transfer Reaction Mass Spectrometry

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.     

Spatially resolved measurements of ion density behind the skimmer of an inductively coupled plasma mass spectrometer

Ions are extracted from the inductively coupled plasma through a conventional sampler and skimmer and then deposited on an array of graphite targets at the exit of a set of electrostatic ion lenses. The Sc⁺ signal is enhanced by choosing appropriate potentials on the ion lenses. The Sc⁺ signal is suppressed by the presence of concomitant Cs ions at high concentrations. Comparisons of grounded ion lenses and two different ion lens potential settings are made. The signal is enhanced more extensively by the ion lenses when there are no concentrated concomitant ions. This study indicates that matrix effects in inductively coupled plasma mass spectrometry could possibly be alleviated by choosing ion lens potentials such that the ions enter the ion optics with a relatively broad beam cross section, the beam then being focused to a smaller size. A photon stop inside the ion lens stack reduces ion transmission and changes the shape of the beam profile from conical to bimodal.     

Evolution of instrumentation for the study of gas-phase ion/ion chemistry via mass spectrometry

The scope of gas-phase ion/ion chemistry accessible to mass spectrometry is largely defined by the available tools. Due to the development of novel instrumentation, a wide range of reaction phenomenologies has been noted, many of which have been studied extensively and exploited for analytical applications. This perspective presents the development of mass spectrometry-based instrumentation for the study of the gas-phase ion/ion chemistry in which at least one of the reactants is multiply charged. The instrument evolution is presented within the context of three essential elements required for any ion/ion reaction study: the ionization source(s), the reaction vessel or environment, and the mass analyzer. Ionization source arrangements have included source combinations that allow for reactions between multiply charged ions of one polarity and singly charged ions of opposite polarity, arrangements that enable the study of reactions of multiply charged ions of opposite polarity and, most recently, arrangements that allow for ion formation from more than two ion sources. Gas-phase ion/ion reaction studies have been performed at near atmospheric pressure in flow reactor designs and within electrodynamic ion traps operated in the mTorr range. With ion trap as a reaction vessel, ionization and reaction processes can be independently optimized and ion/ion reactions can be implemented within the context of MSn experiments. Spatial separation of the reaction vessel from the mass analyzer allows for the use of any form of mass analysis in conjunction with ion/ion reactions. Time-of-flight mass analysis, for example, has provided significant improvements in mass analysis figures of merit relative to mass filters and ion traps.     

离子色谱法分析金属离子的研究进展

综述了离子色谱法(IC)分析金属离子的研究进展,对目前应用于分析金属离子的阳离子交换IC、阴离子交换IC和螯合离子色谱进行了评述。阳离子交换IC是IC分析金属离子的主要形式,固定相为强酸(磺酸)型阳离子交换剂和弱酸(羧酸)型阳离子交换剂,结合适当的检测方法,阳离子交换IC可以测定碱金属、碱土金属、过渡金属、稀土离子、铵离子及低相对分子质量的有机胺类分子等。阴离子交换IC可以分析碱土金属、过渡金属、稀土离子等,对金属离子的分析具有更好的选择性,并可以实现金属离子和无机阴离子的同时测定。螯合离子色谱可以对复杂基体中的痕量金属离子进行测定。引用文献125篇。     

Adduction of solvent molecules by ions isolated within an ion trap mass spectrometer under atmospheric pressure ionisation conditions

Benzylpyridine and papaverine, an alkyl quinoline, both produce product ions containing an azepinium ring during atmospheric pressure chemical ionisation or electrospray multistage mass spectrometry. By controlling the trapping conditions, an isolated azepinium ion was held within the trap for an extended period of time without excitation. A subsequent analytical scan revealed a mass spectrum containing ions at two mass-to-charge (m/z) ratios, the first at the m/z of the isolated product ion and the second at an m/z ratio corresponding to the adduction of a molecule of solvent. Isolation and resonance excitation of the adduct ion remove the solvent molecule, resulting in recovery of the azepinium ion at the same signal intensity as the adduct ion. Isolating and trapping the ion for a further period allowed the solvent adduct ion to be re-formed. Modulation of the solvent flowing into the source while the ion was trapped allowed variation in the solvent molecule adducted to the trapped ion. The proportion of the ion current due to the adduct ion depends on the nature of the isolated ion, the proton affinity of the solvent and the length of time for which the ion was trapped. Adduct ion formation, deliberately maximised in this study, can occur to a significant extent under standard ion trap operating conditions, reducing the ion current of product ions of interest and, ultimately, the response in tandem mass spectrometric assays.     

The effect of the ion exchanger site-counterion complex formation on the selectivities of ISEs

Using the model of ideally associated solution, the effect of ion association of the ion exchanger sites with main and foreign counterions on the selectivity of ISEs based on liquid ion exchangers has been considered. Equations which describe the potentiometric selectivity coefficient as a function of ion association constants in the membrane phase and of standard free energies of transfer of the determined and foreign ions from water to the membrane are obtained for the following main cases: (a) the determined and foreign ions are single-charged; (b) the determined ion is double-charged and the foreign ion is single-charged. It is shown that in the case of single-charged main and foreign ions, the ratio of the ion association constants has a great effect on the potentiometric selectivity of membranes, only if the ion exchanger sites produce less strong associates with the determined counterion as compared with the foreign one. Otherwise, this effect is insignificant. The selectivity for double-charged ions should increase, other things being equal, as the first constant of association of these ions with the ion exchanger sites increases. The effect of producing ion triplets of the type I(2)R((+/-)) on the selectivity of ISEs is also considered. Experimental data are presented which illustrate the effect of the nature of the ion exchanger on the potentiometric selectivity. Some procedures employing the factor of ion association for increasing the potentiometric selectivity of liquid ion exchange membranes are considered.     

Current efficiency and titration efficiency in coulometric titrations with electrogenerated ceric ion determination of iodide

The current efficiency for the electrogeneration of cerie ion at a platinum anode falls considerably below 100% at both very small and at large current densities in both sulfuric and perchloric acid media. The maximal current efficiency is about 99.8%.Iodide ion can be titrated to iodine with an error of only about +0.3%, even under conditions where the cerie ion generation efficiency is only 98%. High titration efficiency, in spite of poor efficiency for ceric ion generation, is obtained because iodine is oxidized to iodate ion at a potential slightly in advance of the potential at which cerous ion is oxidized. Since the electrogenerated iodate ion oxidizes iodide ion only a minor fraction of the total quantity of electricity results from ceric ion generation, so the effect of its inefficient generation is greatly minimized. Satisfactory titrations of iodide ion to iodine can be performed without any cerous salt present, provided the generating current density is smaller than the limiting current density for oxidation of iodine to iodate ion.     

Key fragments for identification of positional isomer pair in glucuronides from the hydroxylated metabolites of RT-3003 (Vintoperol) by liquid chromatography/electrospray ionization mass spectrometry.

The mass spectral properties of glucuronides of the 9- and 10-hydroxylated metabolites of RT-3003 (Vintoperol; (-)-1beta-ethyl-1alpha-hydroxymethyl-1,2,3,4,6,7, 12balpha-octahydroindolo[2,3-a]quinolizine), which were fractionated by high-performance liquid chromatography with fluorescence detection, were investigated using the positive ion electrospray ionization mode. These glucuronides showed predominantly the protonated molecular ion ([M + H](+) ion), and the [M + H](+) ion provided a characteristic product ion spectrum in which abundant ions were obtained at m/z 301, 160 and 142. The first ion, corresponding to the [aglycone + H](+) ion, was produced by neutral loss of the glucuronic acid moiety from the [M + H](+) ion. The product ion spectrum of the [M + H](+) ion of hydroxy-RT-3003 revealed a number of ions common to the glucuronide spectra, suggesting that other two ions observed most likely represent fragmentation of hydroxy-RT-3003. In turn, these glucuronides were positional isomers with respect to the binding site of glucuronic acid. The structures of the isomer pairs were discriminated by the presence of the ion of m/z 318 or 336 in the product ion spectrum. These ions were produced by fission of the C-ring, the same as for the formation of the ions of m/z 160 and 142, as were observed in the product ion spectrum from the [M + H](+) ion of hydroxy-RT-3003. For the formation of these ions, an unusual fragmentation process was proposed, and these ion structures were supported by evidence from the accurate mass measurement data. Additionally, in the sulfates of hydroxylated metabolites, a similar product ion corresponding to the ion of m/z 336 found in the phenolic glucuronides was observed, and was applied for identification of the sulfate metabolites.     

Use of a kinetic energy orifice as a probe of metastable dissociation in Fourier transform ion cyclotron resonance mass spectrometry

Although Fourier transform ion cyclotron resonance mass spectrometry is a powerful tool in the qualitative observation of gas phase reactions, ion detection is on the millisecond time scale, orders of magnitude longer than typically found when using a sector instrument. Observations of short-lived species such as chemically activated adduct ions can be accomplished using selective ion excitation as a probe of intermediate lifetime. Whereas ion elimination has been shown to be effective in monitoring ion lifetimes on the microsecond time scale, problems associated with detecting ions produced with high kinetic energies limits the technique. Use of a kinetic energy orifice as an ion skimmer effectively eliminates ions near the center of the ion cell at relatively low kinetic energies. By modifying a single section cell to include a kinetic energy orifice, the lifetimes of chemically activated adduct ions have been investigated.     

杯[4]芳烃衍生物对Pb2＋的液膜传输动力学

以3类含不同基团的杯[4]芳烃衍生物作为离子载体在H2O-CHCl3-H2O液膜传输体系下分别对Pb2＋进行液膜传输实验. 简要讨论了以杯[4]芳烃衍生物作为离子载体对Pb2＋液膜传输的动力学机理. 重点研究了不同载体种类, 载体浓度, 搅拌速度, 传输时间等因素对Pb2＋传输的影响. 实验结果表明: 以含Br原子的杯[4]芳烃衍生物和含S原子的杯[4]芳烃衍生物作为离子载体对Pb2＋有明显的传输效果. 可以用本文的动力学模型来描述整个传输体系的动力学特性.     

海藻酸-壳聚糖-海藻酸凝胶离子取代机理

研究了海藻酸-壳聚糖-海藻酸(ACA)凝胶的离子取代机理.光学显微镜照相法证实ACA离子取代过程中溶胶-凝胶相界面的存在.动边界模型描述ACA离子取代凝胶对二价离子的取代动力学过程,结果表明,模型可靠.离子取代凝胶对二价离子的取代属于颗粒扩散控制机理.与离子交换树脂比较,ACA离子取代速率要快得多,ACA离子取代过程不同于传统离子交换树脂离子交换过程,它是金属离子在溶胶凝胶相转移过程中的取代过程;ACA是一种崭新的离子移变凝胶型离子吸附剂.     

The coupling effects of hexapole and octopole fields in quadrupole ion traps: a theoretical study

A theoretical method, the harmonic balance method, was introduced to study the coupling effects of hexapole and octopole fields on ion motion in a quadrupole ion trap. Ion motion characteristics, such as ion motion center displacement, ion secular frequency shift, nonlinear resonance curve and buffer gas damping effects, have been studied with the presence of both hexapole and octopole fields. It is found that hexapole fields have bigger impacts on ion motion center displacement, while octopole fields dominate ion secular frequency shift. Furthermore, the nonlinear features originated from hexapole and octopole fields could enhance or cancel each other, which provide us more space in a practical ion trap design process. As an example, an ion trap with improved performance was designed using a specific combination of hexapole and octopole fields. In this ion trap, a hexapole field was used to achieve efficient ion directional ejection, while an octopole field was added to correct the chemical mass shift and resolution degradation introduced by the hexapole field. Copyright © 2013 John Wiley & Sons, Ltd.     

The influence of ion beam sputtering on the composition of the near-surface region of silicon carbide layers

The concentrations and the lattice structure of silicon carbide layers and single crystals are influenced by ion beam sputtering. The influence of ion beam sputtering and primary ion energy on preferential sputtering is investigated by Auger measurements and T-DYN simulations. In dependence on primary ion energy C is enriched. Preferential sputtering increases with decreasing ion energy. Sputtering has a strong influence on the Auger peak shapes of SiC. Except for low ion energy and glancing incidence the peak shapes are independent of the primary ion energy. T-DYN simulations help to explain and understand the near-surface processes during sputtering of SiC. For ion energy dependence of preferential sputtering there is a good agreement of the T-DYN simulation and the Auger measurement. Received: 10 October 1998 / Revised: 26 March 1999 / Accepted: 2 April 1999     

DC Potentials Applied to an End-cap Electrode of a 3-D Ion Trap for Enhanced MS Functionality

The effects of the application of various DC magnitudes and polarities to an end-cap of a 3-D quadrupole ion trap throughout a mass spectrometry experiment were investigated. Application of a monopolar DC field was achieved by applying a DC potential to the exit end-cap electrode, while maintaining the entrance end-cap electrode at ground potential. Control over the monopolar DC magnitude and polarity during time periods associated with ion accumulation, mass analysis, ion isolation, ion/ion reaction, and ion activation can have various desirable effects. Included amongst these are increased ion capture efficiency, increased ion ejection efficiency during mass analysis, effective isolation of ions using lower AC resonance ejection amplitudes, improved temporal control of the overlap of oppositely charged ion populations, and the performance of "broad-band" collision induced dissociation (CID). These results suggest general means to improve the performance of the 3-D ion trap in a variety of mass spectrometry and tandem mass spectrometry experiments.     

The use of static pressures of heavy gases within a quadrupole ion trap

The performance of quadrupole ion traps using argon or air as the buffer gas was evaluated and compared to the standard helium only operation. In all cases a pure buffer gas, not mixtures of gases, was investigated. Experiments were performed on a Bruker Esquire ion trap, a Finnigan LCQ, and a Finnigan ITMS for comparison. The heavier gases were found to have some advantages, particularly in the areas of sensitivity and collision-induced dissociation efficiency; however, there is a significant resolution loss due to dissociation and/or scattering of ions. Additionally, the heavier gases were found to affect ion activation and deactivation during MS/MS, influencing the product ion intensities observed. Finally, the specific quadrupole ion trap design and the ion ejection parameters were found to be crucial in the quality of the spectra obtained in the presence of heavy gases. Operation with static pressures of heavy gases can be beneficial under certain design and operating conditions of the quadrupole ion trap.     

Structure and fragmentation of b2 ions in peptide mass spectra

In a number of cases the b2 ion observed in peptide mass spectra fragments directly to the a1 ion. The present study examines the scope of this reaction and provides evidence as to the structure(s) of the b2 ions undergoing fragmentation to the a1 ion. The b2 ion H-Ala-Gly+ fragments, in part, to the a1 ion, whereas the isomeric b2 ion H-Gly-Ala+ does not fragment to the a1 ion. Ab initio calculations of ion energies show that this different behavior can be rationalized in terms of protonated oxazolone structures for the b2 ions provided one assumes a reverse activation energy of approximately 1 eV for the reaction b2-->a2; such a reverse activation energy is consistent with experimental kinetic energy release measurements. Experimentally, the H-Aib-Ala+ b2 ion, which must have a protonated oxazolone structure, fragments extensively to the a1 ion. We conclude that the proposal by Eckart et al. (J. Am. Soc. Mass Spectrom. 1998, 9, 1002) that the b2 ions which undergo fragmentation to a1 ions have an immonium ion structure is not necessary to rationalize the results, but that the fragmentation does occur from a protonated oxazolone structure. It is shown that the b2-->a1 reaction occurs extensively when the C-terminus residue in the b2 ion is Gly and with less facility when the C-terminus residue is Ala. When the C-terminus residue is Val or larger, the b2-->a1 reaction cannot compete with the b2-->a2 fragmentation reaction. Some preliminary results on the fragmentation of a2 ions are reported.     

Comparative studies of SIMS and SNMS analyses during the build up of sputter equilibrium under oxygen and rare gas ion bombardment

Sputtering of solid surfaces by using a focused ion beam is the basis for secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS). The ion bombardment initiates not only redistribution of sample atoms but also massive changes in the surface and near surface composition of the bombarded area due to the sputter process and implantation of the primary ions. Changes in the matrix-composition affects the secondary ion yields and therefore a steady state (sputter equilibrium) has to be reached before SIMS data can give quantifiable results. SNMS is much less affected by those yield effects and therefore a combination of SIMS and SNMS can establish a basis for interpretation of SIMS data before the steady state is reached. In order to determine the effects of primary ion incorporation, we applied different primary ion species successively to generate different equilibria. An oxygen ion beam oxidizes the sample surface and by using a rare gas primary ion (PI) this oxide can be removed and analyzed.     

Space charge effect in spectrometers of ion mobility increment with planar drift chamber

The effect of space charge on the ion beam in a spectrometer of ion mobility increment with the planar drift chamber has been investigated. A model for the drift of ions under a non-uniform high-frequency electric field(1-3) has been developed recently. We have amplified this model by taking space charge effect into account. The ion peak shape taking into consideration the space charge effect is obtained. The output current saturation effect limiting the rise of the ion peak with increasing ion density at the input of the drift chamber of a spectrometer is observed. We show that the saturation effect is caused by the following phenomenon. The maximum possible output ion density exists, depending on the ion type (constant ion mobility, k(0)) and the time of the motion of ions through the drift chamber. At the same time, the ion density does not depend on the parameters of the drift chamber.     

Applications of a travelling wave-based radio-frequency-only stacked ring ion guide

The use of radio-frequency (RF)-only ion guides for efficient transport of ions through regions of a mass spectrometer where the background gas pressure is relatively high is widespread in present instrumentation. Whilst multiple collisions between ions and the background gas can be beneficial, for example in inducing fragmentation and/or decreasing the spread in ion energies, the resultant reduction of ion axial velocity can be detrimental in modes of operation where a rapidly changing influx of ions to the gas-filled ion guide needs to be reproduced at the exit. In general, the RF-only ion guides presently in use are based on multipole rod sets. Here we report investigations into a new mode of ion propulsion within an RF ion guide based on a stack of ring electrodes. Ion propulsion is produced by superimposing a voltage pulse on the confining RF of an electrode and then moving the pulse to an adjacent electrode and so on along the guide to provide a travelling voltage wave on which the ions can surf. Through appropriate choice of the travelling wave pulse height, velocity and gas pressure it will be shown that the stacked ring ion guide with the travelling wave is effective as a collision cell in a tandem mass spectrometer where fast mass scanning or switching is required, as an ion mobility separator at pressures around 0.2 mbar, as an ion delivery device for enhancement of duty cycle on an orthogonal acceleration time-of-flight (oa-TOF) mass analyser, and as an ion fragmentation device at higher wave velocities.