一种新型二次离子质谱的一次离子源及其离子光学系统

本研究设计了一种新型用于二次离子质谱的一次离子源及其离子光学系统.通过此一次离子源,大气压下产生的一次离子可以被加速、聚焦并传输到位于真空条件下的样品表面并电离样品得到可供质谱仪分析的二次离子.通过理论模拟结合实验系统研究了此一次离子源的主要组成部分——离子光学系统的原理、结构和性能.以电喷雾电离源为例,成功地将大气压...     

Examination of the best pressure range for ion/molecule reactions of anthraquinones in an external source ion trap mass spectrometer.

This study outlines some observations of the pressure effect for gas phase ion-molecule reactions of anthraquinone derivatives with dimethyl ether in an external source ion trap mass spectrometer. At the reagent pressure of 7.998 x 10(-2) Pa, formation of the protonated ions, [M + 13]+, [M + 15]+, and [M + 45]+ ions, of anthraquinones can be observed. However, at the pressure of 1.066 x 10(-2) Pa, formation of molecular ions and many fragment ions of the M+. or [M + H]+ ions have been observed. Since the pressure effect is notable within a small range of pressures for many compounds, it is important to draw attention to the use of the ion trap with an external source where other factors such as ion source residence time may play a role. This can also provide some information for better and more careful controls of the reagent pressure in order to obtain fair CI spectra in an external source ion trap mass spectrometer.     

Effect of Bleeding Oxygen on Processes in the Ion Source of an EMAL-2 Mass Spectrometer in the Analysis of Oxygen-Containing Samples

When bleeding oxygen into the ion source of an EMAL-2 laser mass spectrometer, an oxygen monolayer was formed on atomically pure sample surfaces produced by laser scanning. It was found that the signal of this oxygen can be used for calculating sensitivity factors. Bleeding oxygen increased the yield of test sample matrix ions; for example, the yield of Fe⁺ ions was doubled. The qualitative analysis of a gas atmosphere introduced into the ion source of an EMAL-2 mass spectrometer can be performed. Chloroform, which was present in a prepared gas mixture, was identified by the lines of molecular ions. The intensity of its molecular lines in the mass spectrum in the case using carbon reagent ions was higher by an order of magnitude than that in the case using silicon.     

Chemical ionization over a wide range of pressures. 1. Mass spectra of dimethyl esters of maleic and fumaric acids

Conclusions By using chemical ionization over a wide range of pressures, from 0.01 torr to atmospheric pressure, and also by selecting the reagent gas, different mass spectra of isomers can be obtained, which are suitable for their reliable identification.Under ionization conditions at atmospheric pressure in helium (reagent ions [H(H₂O)_n]⁺), peaks of cluster ions [MGH]⁺ and [2M+1]⁺ are observed in the spectrum of dimethyl fumarate, which are absent in the case of the cis-isomer.Under the conditions of chemical ionization at a normal pressure (0.4-0.2 torr) of the reagent gases Me₃CH, n-C₇H₁₆ and at an ionic source temperature of 50°C, a stereospecific fragmentation of dimethyl maleate [MH]⁺-MeOH is observed, which is absent in the case of the the trans-isomer.In the chemical ionization spectra at reduced pressure of the reagent gases MeOH, EtOH, i-PrOH (0.01 torr), a peak of the cluster ion [MGH]⁺ is observed for dimethyl fumarate, which is absent in the spectra of the cis-isomer.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 815–819, April, 1985.     

Ammonia laser desorption/chemical ionization with ammonium bromide: Fourier transform ion cyclotron resonance mass spectrometry of aromatic hydrocarbons

Laser desorption/ionization combined with Fourier transform ion cylcotron resonance mass spectrometry (LD/FT/ICR/MS) is a proven technique for the analysis of nonvolatile materials. Unfortunately, LD tends to produce a large excess of neutral species compared to ions. Laser desorption followed by chemical ionization (LD/CI) by use of a reagent gas is a seIective and sensitive means of control in the analysis of nonvolatile compounds. In this article we demonstrate the technique of ammonia LD/CI by addition of a small amount of ammonium bromide (NH₄Br) to an involatile sample, i.e., the ammonium salt is used in place of ammonia reagent gas. For various aromatic hydrocarbons, abundant (M + H)⁺ ions are produced as a result of CI A primary advantage of this method in FT/ICR/MS is that selective LD/CI experiments may be conducted at low pressure as in pulsed valve CI (but without the need for pulsed valve operation), thereby providing the potential for obtaining high-resolution FT/ICR mass spectra.     

Capillary Gas Chromatography Coupled with Microplasma Mass Spectrometry – Improved Ion Source Design Compatible with Bench-Top Mass Spectrometric Instrumentation

Capillary gas chromatography was performed with mass spectrometric detection using a novel microplasma ion source for operation in an element-selective mode. The ion source was a 350 kHz radio frequency helium plasma, which was sustained inside the 4 cm end of a 0.32 mm i.d. fused silica capillary column, and located inside the high vacuum chamber of the quadrupole mass spectrometer. Due to the low volume of the ion source, a stable low pressure discharge was produced utilizing only the 2.25 mL min⁻¹ of GC carrier gas (helium) for plasma support. Small amounts of oxygen (0.1–0.2% v/v) were added to the plasma gas in order to prevent carbon deposits and to enhance signal-to-noise ratios. Chlorine and bromine were selectively detected at the 5–20 pg s⁻¹ level (S/N = 2), and both produced a response that was linear within 3 orders of magnitude.     

Super-Atmospheric Pressure Electrospray Ion Source: Applied to Aqueous Solution

This is a follow-up paper of our previous report on an ion source, which was operated at an operating pressure higher than the atmospheric pressure. Besides having more working gas for desolvation, the reduction of mean free path of electrons in a higher pressure environment increases the threshold voltage for gaseous breakdown, thus enabling a stable electrospray for the sample solution with high surface tension without the occurrence of electric discharge. In our previous work, the ion source was not coupled directly to the mass spectrometer and significant amount of ions were lost before entering the vacuum of the mass spectrometer. In this paper, we report the new design of our second prototype in which, by using a modified ion transport capillary, the pressurized ESI ion source was coupled directly to the first pumping stage of the mass spectrometer without additional modification on the vacuum pumping system. Demonstrations of the new ion source on the sensitive detection of native proteins from aqueous solution in both positive and negative ion modes are presented.     

Methylene substitution reactions in a quadrupole ion trap selectivity of ethylene,ethylene oxide,and dimethyl ether reactive ions

To elucidate the selectivity of methylene substitution reactions of monosubstituted and disubstituted oxyaromatic compounds in a low pressure quadrupole ion trap environment, the relative abundances of covalently bound and loosely bound adducts formed by ion/molecule reactions with ethylene (ET), ethylene oxide (ETOX), and dimethyl ether (DME) were compared. Adduct ions of all three reagent gases were formed in both a conventional ion source and a quadrupole ion trap and characterized by collisionally activated dissociation. For DME and ET, the covalently bound adducts formed at (M + 45)⁺ and (M + 41)⁺, respectively, are direct precursors to the methylene substitution product ions at (M + 13)⁺. ETOX and ET do not demonstrate the same functional group selectivity for methylene substitution as previously observed for DME. This is attributed to differences in reaction exothermicities and competing reactions.     

Direct exposure chemical ionization mass spectra of explosives

Mass spectra of explosives, including TNT, tetryl, nitroglycerin, PETN and RDX have been recorded by direct exposure chemical ionization with isobutane as reagent at source temperatures of 50–100°C. The mass spectra contain major [MH]⁺ ions, adduct ions and some fragment ions. The configuration of the relative abundances of these ions has been found to be a function of temperature and source pressure. Maximum [MH]⁺ ion abundance has been obtained at source pressures much lower than normal chemical ionization pressures.     

Formation of an unusual MH− ion in the methane negative-ion chemical ionization mass spectra of chlorprothixene and aromatic sulfur compounds

The methane negative-ion chemical ionization (NCI) mass spectrum of chlorprothixene shows an unusual MH^? ion. This ion can be accounted for by electron capture followed by H˙ transfer from the reagent gas. The most probable site of electron attachment was concluded to be related to the sulfur atom of the thioxanthene ring based on the observation of analogous ions for structurally related compounds, all containing a heterocyclic sulfur. The MH^? ion observed with methane as the reagent gas was shifted to MD^? when tetradeuteromethane was used in place of methane. The ratio of [M ? H]^? to MH^? did not change with emission current suggesting that the process is independent of the radical concentration in the CI plasma. Consistent with this observation is the lack of CH₃˙ or C₂H₅˙ adduct ions in the NCI mass spectrum and the fact that gold-plating the ion source did not decrease the proportion of MH^?. Also, this mechanism is consistent with thermochemical considerations of reactions of a phenyl radical with various alkanes and observations of ions formed by methane NCI from model compounds. Therefore, unlike other MH^? ions observed in methane NCI mass spectra, the mechanism of formation does not appear to involve a hydrogen radical addition followed by electron capture.     

Cu+ chemical ionization for analysis of hydrocarbons by gas chromatography/mass spectrometry

The use of copper ions for chemical ionization (CI) coupled with gas chromatography/mass spectrometry (GC/MS) of hydrocarbons is reported. Cu⁺?CI was performed in a high-pressure, fast atom bombardment ion source coupled with both a gas chromatograph and a mass spectrometer. The suitability of the Cu⁺?CI method is illustrated by the analysis of pure alkylbenzenes, alkylthiophenes, octenes, and by the analysis of a light mixture of aromatic hydrocarbons. The Cu⁺?CI/GC mass spectra display an abundant [M+⁶³Cu]⁺ ion, together with fragmentations, that are of structural interest. The detection limit for isobutylbenzene, taken as model compound, is 100 times lower than that for electron ionization.     

Comparing differentiation of xylene isomers by electronic ionization, chemical ionization and self-ion/molecule reactions and the first observation of methyne addition ions for xylene isomers in self-ion/molecule reactions for non-nitrogenated compounds

This study presents the self-ion/molecule reaction (SIMR) spectra of three xylene isomers, and proposes an approach to differentiating them based on observed differences in relative abundances of ions formed by SIMR in an internal source ion trap instrument. It also demonstrates the applicability of SIMR for isomer discrimination, which is better than electron ionization (EI) and dimethyl ether chemical ionization (DME CI) in an ion trap mass spectrometer (ITMS) since no CI reagent, metal ions or internal standards are required to perform SIMR. The merits of the new method for distinguishing isomers are that it is simple, rapid and economic. To date, methyne addition products ([M+13](+) ions) have been observed for several nitrogenated compounds including aza-crown ethers, aniline and dopamine from SIMR in the ITMS. The xylene isomers are, however, the first three non-nitrogenated compounds that have been shown to produce the methyne addition ions in SIMR.     

Reduction of trinitroaromatic compounds in water by chemical ionization mass spectrometry

A reduction process was found to occur in the ion source when observing the chemical ionization mass spectra of a series of trinitroaromatic compounds, using water as reagent. The [MH–30]⁺ ions in the CI mass spectra were due mainly to the reduction of the compounds to their corresponding amines. This was proved by using D₂O as reagent: the [MH–30]⁺ ions were shifted to [MD–28]⁺ ions. The trinitroaromatic compounds investigated included 1,3,5-trinitrobenzene, 2,4,6-trinitrotoluene, 2,4,6-trinitro-m-cresol, 2,4,6-trinitroaniline (picramide) and 2,4,6-trinitrophenol (picric acid).     

Numerical Simulation of Ion Transport in a Nano-Electrospray Ion Source at Atmospheric Pressure

Understanding ion transport properties from the ion source to the mass spectrometer (MS) is essential for optimizing device performance. Numerical simulation helps in understanding of ion transport properties and, furthermore, facilitates instrument design. In contrast to previously reported numerical studies, ion transport simulations in a continuous injection mode whilst considering realistic space-charge effects have been carried out. The flow field was solved using Reynolds-averaged Navier-Stokes (RANS) equations, and a particle-in-cell (PIC) method was applied to solve a time-dependent electric field with local charge density. A series of ion transport simulations were carried out at different cone gas flow rates, ion source currents, and capillary voltages. A force evaluation analysis reveals that the electric force, the drag force, and the Brownian force are the three dominant forces acting on the ions. Both the experimental and simulation results indicate that cone gas flow rates of ≤250 slph (standard liter per hour) are important for high ion transmission efficiency, as higher cone gas flow rates reduce the ion signal significantly. The simulation results also show that the ion transmission efficiency reduces exponentially with an increased ion source current. Additionally, the ion loss due to space-charge effects has been found to be predominant at a higher ion source current, a lower capillary voltage, and a stronger cone gas counterflow. The interaction of the ion driving force, ion opposing force, and ion dispersion is discussed to illustrate ion transport mechanism in the ion source at atmospheric pressure.

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Graphical Abstract

     

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.     

Negative Corona Discharge Ion Source Under Ambient Conditions with Mini Line-cylinder Electrodes

A novel ambient negative corona discharge ion source with mini line-cylinder electrodes is designed. The diameters of inner and outer electrode are 0.16 and 4 mm respectively. With a special assembly method, a perfect coaxiality of the two electrodes is obtained. An injection system utilizing a temperature control technique, achieves a constant and stable concentration of the sample, which is critical to the experiment. The formulas of the corona onset voltage of line-cylinder electrodes are also introduced. The experiment results show that negative substances such as formic acid and acetic acid can be ionized under ambient conditions. When combined with micro electrical mechanical system fabricationprocess, the volume of the ion source can be reduced dramatically, but there is an undesirable surface discharge. To solve the surface discharge problem, an improved structure was designed and tested. The simplicity of the interface of the ion source makes it suitable for mass spectrometer, micro mass spectrometer, ion mobility spectrometer, and high-field asymmetric waveform ion mobility spectrometer applications.     

Electron and chemical ionization mass spectrometry in stereochemical differentiation of some 1,3-amino alcohols

Mass spectral fragmentations of two cyclopentane, eight cyclohexane and four norbornane/one 1,3-amino alcohols were studied under electron ionization (EI) by low-resolution, high-resolution, metastable ion analysis and collision-induced dissociation (CID) techniques. All stereoisomeric compounds gave rise to identical 70 eV EI mass spectra. However, the spectra of positional isomers clearly differed. The main fragmentation pathway for the saturated compounds began as an α-cleavage reaction with respect to the nitrogen atom. For the norbornene compounds a retro-Diels—Alder reaction was favoured. Relative to the aminomethyl-substituted compounds the fragmentation patterns for the compounds having the amino group connected directly to the ring were more complicated. The chemical ionization (CI) mass spectra were recorded using ammonia, isobutane, methane, dichloromethane and acetone as reagent gas. From the norbornane/One compounds the di-exo isomers decomposed more easily than the di-endo isomers with most of the reagent gases used. Differences between stereoisomers were observed directly only under methane CI. The decomposition products of the [M + H]⁺ ions generated under ammonia and isobutane CI were studies by recording their CID mass spectra. These spectra allowed the differentiation of the stereoisomers, at least to some extent.     

If the ionization mechanism in fast-atom bombardment involves ion/molecule reactions, what are the reagent ions? The time dependence of fast-atom bombardment mass spectra and parallels to chemical ionization

The evaporation in vacuo of the matrices used and the particle-induced desorption of matrix molecules in fast-atom bombardment (FAB) contribute to a proposed high pressure region above the FAB matrix known as the selvedge region. If the neutral number density is sufficiently high, ions formed upon bombardment may undergo collisions with molecules, yielding matrix-related cluster ions and, in cases when the analyte is desorbed in neutral form, protonated and deprotonated analyte molecules. Similarities with the chemical ionization (CI experiment have been pointed out previously and are further developed here. If FAB is similar to CI, then the response depends on the structures of the reagent ions — those ions that react with gas phase analyte molecules. We consider here the time dependence of positive and negative ion FAB spectra to attempt to identify the reagent ions of FAB. A model is suggested for the FAB ion source which evaluates similarities to a CI source, as well as spatial aspects that are unique to desorption/ionization techniques.     

表面离化源工作参数对离子迁移率谱的影响

根据表面离化过程中样品分子在离化材料表面直接离化的特点,设计了一种样品离化和离子注入一步完成的面-网结构表面离化源.以金属钼为离化材料,三乙胺为测试样品,研究了离化源温度、离子门开门脉冲宽度和高度对离子谱图的影响.结果表明,离子流信号强度随离化温度升高迅速增强但离化源寿命缩短,理想的离化温度约为400℃；增加开门脉冲宽...     

一种用于高场非对称波形离子迁移谱系统的新型敞开式化学离子源

根据高场非对称波形离子迁移谱(FAIMS)系统的要求, 本文提出了一种新型敞开式直流电晕放电化学离子源. 该离子源主要由内线电极、外筒电极和牵引电极组成, 内、外电极半径分别是0.08、2 mm. 筒壁电极上开有对称的4个槽, 用于通入样品和牵引离子. 质谱实验结果表明, 该离子源能够在敞开环境下很好地离子化丙酮、乙醇、苯胺、N,N-二甲基甲酰胺、甲基磷酸二甲酯(DMMP)、乙酸乙酯、甲酸、乙酸、苯酚等正、负电性物质. 静电计测试实验结果说明该离子源能够稳定地产生离子电流. 通过分析不同时刻的谱图发现, 在不同时间点上产生的主要离子相同, 具有很好的稳定性. 利用感应耦合等离子体(ICP)工艺在硅片上加工了该离子源, 从而验证了该结构可以由微机电系统(MEMS)加工技术实现. 该离子源具有体积小、结构简单、无辐射、工作稳定等特点, 不仅可以满足FAIMS系统的要求, 还可用于敞开式质谱、微型质谱仪、离子迁移谱(IMS)等仪器.