离子在矩形波四极场中的运动与四极场离子阱质谱的数字化操作

矩形波驱动的四极场同样可用于对离子进行质量分析和存储，本推导了离子在矩形波四极场中的运动规律，并以常用于正弦波四极场的马绍方程参量a,q来表离子的稳定性，运用赝势阱概念探讨了离子在这种四极场中的本征振动，推导了本征振动频率的近似公式，在理论研究的基础上，提出了数字化离子阱质谱的概念，并运用离子光学模拟，研究了实际离子阱几何结构下的共振出射以及数字以质量扫描的可行性。     

优化修正入口边缘场四极质谱计离子光学特性的模拟计算

对一种具有优化修正入口边缘场的四极质谱计离子光学特性用相空间力学分析方法进行了模拟计算,给出了模拟计算的要点和结果分析,模拟结果与实验结果很好地一致,从面 理论上进一步证明了这种四极质谱计的可行性。     

矩形离子阱质量分析过程的数值模拟

传统的四极离子阱质量分析器中离子的运动可用二阶线性微分方程——Mathieu方程的解来描述。根据Mathieu稳定图所反映的离子运动特性,可实现离子的质谱分析。但Mathieu方程对平板电极的矩形离子阱描述不再准确适用,本文通过数值模拟的方法,依次对矩形离子阱质量分析器内电场分布、离子运动轨迹、离子阱的Mathieu稳定图以及标准工作模式下获得的质谱图进行了模拟和分析。     

质谱仪四极杆质量分析器的研制

四极杆质谱仪是目前最成熟、应用最广泛的小型质谱仪.四极杆质量分析器通过在双曲四极杆上接入射频信号产生四极场,离子在四极场中受到强聚焦作用而向分析器的中心轴聚焦.四极杆质量分析器中离子的运动在数学上可用二阶线性微分方程Mathieu方程的解来描述,利用离子在Mathieu方程解的稳定性图中所具有的特性,可实现离子的质谱扫描.己成功地制造出四极杆质量分析器试件,并初步掌握了其生产、测试与调试工艺,为质谱仪国产化提供了一定的技术保障.     

优化修正入口边缘场四极质谱计离子光学特性的模拟计算

对一种具有优化修正入口边缘场的四极质谱计离子光学特性用相空间力学分析方法进行了模拟计算 ,给出了模拟计算的要点和结果分析。模拟结果与实验结果很好地一致 ,从而在理论上进一步证明了这种四极质谱计的可行性。     

不同参数四极杆组件宽质量范围性能仿真北大核心CSCD

四极质谱计应用需求的不断扩大对四极杆组件需求量迅速增加,为满足大批量、通用化要求需研发几种固定尺寸的模块化四极杆组件,再设计不同的射频电源来满足应用需求。基于四极电场和离子运动理论,使用离子光学仿真软件SIMION对电场分布和离子运动轨迹进行了建模和计算分析。仿真分析结果表明,在所选定仿真参数下,场半径主要决定大质荷比离子通过率曲线形状,其对不同质荷比离子通过率影响不同,对分辨率的影响随质荷比增大而减小;质荷比越小,离子稳定分离所需杆长越长,达到所需杆长前,离子通过率随杆长增加而减小,分辨率相反;直交比的增加会减小通过率、提高分辨率,对大质荷比段影响更大;频率的增加在全质荷比提高分辨率,增加低质荷比通过率,但显著降低大质荷比通过率;大尺寸杆特别适用于低质荷比离子分析,用于大质荷比时必须采取降低边缘场影响的措施。研究结果可为不同应用目的四极质谱计的设计提供参考。     

基于COMSOL的四极质谱离子运动仿真研究

四极杆质量分析器(即四极质谱仪)因其结构简单、价格较低,被广泛应用于各分析测量领域。围绕着四极杆质量分析器的使用要求,基于四极场离子运动理论基础,结合粒子碰撞理论,利用有限元分析软件COMSOL对四极场电压进行了仿真模拟。结合电场仿真的结果,对四极场中离子轨迹进行了仿真研究。仿真分析了压强大小以及a、q值对离子轨迹和通过率的影响。结果表明四极杆质量分析器应在低于10-2Pa压强下运行。在q值不变情况下,a值的增大会导致通过率降低,另外,q值大小对离子通过率也有较大影响。仿真结果为探索四极杆质量分析器的研制可提供理论和技术上的支持。     

一组四极质谱计的高压力特性

着重给出了一组四极质谱计在高压力范围的工作特性。选用了四种不同长度的圆杆四级滤质器进行研究。所选圆杆四级滤质器的场半径均为2.744mm,场长度分别为30mm、50mm、80mm、140mm。所有四极质谱计都采用尼尔型离子源,离子检测器采用法拉第筒,并且在相同的条件下进行研究。实验结果表明:仪器的线性与滤质器的几何长度、工作频率以及离子进入滤质器的轴向能量有关。分析实验结果认为:滤质器中的离子与离子或分子的碰撞损失效应是决定四极滤质器线性的主要因素。同时还研究了离子进入滤质器时的能量分散对仪器分辨本领的影响,给出了高压力四极质谱计设计的一条有效途径。     

共振对四极滤质器中离子运动的影响

四极滤质器上使用辅助激励电压进行质谱分析时,当辅助激励电压的频率等于或接近四极场中离子运动的基频或谐振频率,就会引发共振现象。使用Matlab软件,对这一现象进行了仿真分析。在设定条件下,以一定步长逐渐增加辅助激励电压交流成分(RF电压)的频率,观察离子振荡幅度的变化。结果表明:在x和y方向的多个不同频率的辅助激励电压作用下,都出现了明显的共振现象。     

四极质谱计非线性区的测量方法

通过离子在四极滤质器中与周围离子或分子碰撞现象的分析研究,对离子与离子或分子的碰撞损失模型进行了修正。导出了四极质谱计测量分压力的普遍关系式。利用这一关系式,可以解决四极质谱计在较高压力非线性医的测量问题。     

四极质谱计灵敏度与离子源参数关系的实验研究

本文通过改变QMS4 2 2型四极质谱计离子源的发射电流、阴极电压和聚焦电压等参数值 ,测量了质谱计灵敏度的相应变化 ,给出并分析了实验结果。实验结果表明 ,对质谱计离子源参数进行调节 ,可以优化质谱计的灵敏度并使之达到最大值     

Dynamic pressure measurements during pulsed gas injection in a quadrupole ion trap

A quadrupole ion trap has been modified to perform dynamic pressure measurements during pulsed introduction of gases. A continuous electron beam is directed through the ion trap where the gas is ionized via electron impact. Ion and electron currents are monitored on the ring and end-cap electrodes, respectively. Dynamic pressure measurements in a region not accessible to a standard gauge are performed using a static quadrupole field. Characteristic current-voltage curves of the ion-trap gauge are presented and optimum operating conditions of the electron-ion optical system are identified in steady state conditions. The sensitivity of the ion-trap gauge is calibrated at these optimum conditions. In the pulsed gas mode ion and electron signals are measured simultaneously on a fast oscilloscope. The time constant of the circuit for the dynamic measurements is ∼129 μs and pressure variations of ∼10⁻⁴-1 Pa occur within 60-130 ms. The exponential decay of the ion signals is used to calculate pumping speeds for helium and argon gases. The distinctive advantages of pulsed gas injections over the use of static pressures in quadrupole ion-trap mass spectrometry are emphasized.     

Ion soft landing using a rectilinear ion trap mass spectrometer

A new ion soft landing instrument has been built for the controlled deposition of mass selected polyatomic ions. The instrument has been operated with an electrospray ionization source; its major components are an electrodynamic ion funnel to reduce ion loss, a 90-degree bent square quadrupole that prevents deposition of fast neutral molecules onto the landing surface, and a novel rectilinear ion trap (RIT) mass analyzer. The ion trap is elongated (inner dimensions: 8 mm x 10 mm x 10 cm). Three methods of mass analysis have been implemented. (i) A conventional mass-selective instability scan with radial resonance ejection can provide a complete mass spectrum. (ii) The RIT can also be operated as a continuous rf/dc mass filter for isolation and subsequent soft landing of ions of the desired m/ z value. (iii) The 90-degree bent square quadrupole can also be used as a continuous rf/dc mass filter. The mass resolution (50% definition) of the RIT in the trapping mode (radial ion ejection) is approximately 550. Ions from various test mixtures have been mass selected and collected on fluorinated self-assembled monolayers on gold substrates, as verified by analysis of the surface rinses. Desorption electrospray ionization (DESI) has been used to confirm intact deposition of [Val (5)]-Angiotensin I on a surface. Nonmass selective currents up to 1.1 nA and mass-selected currents of up to 500 pA have been collected at the landing surface using continuous rf/dc filtering with the RIT. A quantitative analysis of rinsed surfaces showed that the overall solution-to-solution soft landing yields are between 0.2 and 0.4%. Similar experiments were performed with rf/dc isolation of both arginine and lysine from a mixture using the bent square quadrupole in the rf/dc mode. The unconventional continuous mass selection methods maximize soft landing yields, while still allowing the simple acquisition of full mass spectra.     

A quadrupole ion trap with cylindrical geometry operated in the mass-selective instability mode

A cylindrical geometry ion trap is used to record mass spectra in the mass-selective instability mode. The geometry of the cylindrical ion trap has been optimized to maximize the quadrupole field component relative to the higher-order field content through field calculations using the Poisson/Superfish code and through experimental variation of the electrode structure. The results correspond well with predictions of the calculations. The trap has been used to record mass spectra with better than unit mass resolution, high sensitivity, and a mass/charge range of ～600 Th. Multistage (MS(3)) experiments have been performed, and the Mathieu stability region has been experimentally mapped. The performance of this device compares satisfactorily with that of the hyperbolic ion trap.     

Ion trap/ion mobility/quadrupole/time-of-flight mass spectrometry for peptide mixture analysis

An ion trap/ion mobility/quadrupole/time-of-flight mass spectrometer has been developed for the analysis of peptide mixtures. In this approach, a mixture of peptides is electrosprayed into the gas phase. The mixture of ions that is created is accumulated in an ion trap and periodically injected into a drift tube where ions separate according to differences in gas-phase ion mobilities. Upon exiting the drift tube, ions enter a quadrupole mass filter where a specific mass-to-charge (m/z) ratio can be selected prior to collisional activation in an octopole collision cell. Parent and fragment ions that exit the collision cell are analyzed using a reflectron geometry time-of-flight mass spectrometer. The overall configuration allows different species to be selected according to their mobilities and m/z ratios prior to collision-induced dissociation and final MS analysis. A key parameter in these studies is the pressure of the target gas in the collision cell. Above a critical pressure, the well-defined mobility separation degrades. The approach is demonstrated by examining a mixture of tryptic digest peptides of ubiquitin.     

四极质谱计入口边缘场的优化修正

对四极质谱计入口边缘场提出了一种优化修正的工作模式 :在杆系的结构上采用加有端盖的短杆与长杆串联 ;短杆需有确定的几何长度和电长度 ;纯高频短杆场轴电位随质量扫描同步变化。实验证明该模式使灵敏度得到进一步提高 ,特别在克服质量岐视效应、抗污染方面效果显著。     

用Bessel-Box型能量分析器的离子规和四极质谱计的性能

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Analysis of High Mass-to-Charge Ions in a Quadrupole Ion Trap Mass Spectrometer via an End-Cap Quadrupolar Direct Current Downscan

A method for performing mass-selective instability analysis in a three-dimensional (3-D) quadrupole ion trap is described that involves scanning a direct current (dc) voltage applied to the end-cap electrodes while holding the radio frequency (rf) potential at a fixed value. Rather than eject at the ?(z) = 1 instability line by ramping the amplitude of the drive rf potential applied to the ring electrode, as with the original mass-selective instability scan, this approach effects ion ejection along the ?(z) = 0 instability line in a process identical in principle (though it varies in its method of implementation) to the previously termed "downscan" ( Todd , J. F. J. ; Penman , A. D. ; Smith , R. D. Int. J. Mass Spectrom. Ion Processes 1991 , 106 , 117 - 135 ). A linear scan of the dc amplitude results in a nonlinear mass scale, unlike the conventional resonance ejection scan with a linear scan of the rf amplitude, and the ejection of ions in the direction of high mass-to-charge (m/z) to low m/z. However, the downscan offers some advantages over the traditional rf scan for ions of high m/z values. These include a larger scannable mass range, as well as the opportunity for improved resolution at high mass. These characteristics are demonstrated with ions of m/z 10(4)-10(5).     

Oligonucleotide mixture analysis via electrospray and ion/ion reactions in a quadrupole ion trap

Electrospray ionization combined with ion/ion reactions in a quadrupole ion trap can be used for the direct analysis of oligonucleotide mixtures. Elements to the success of this approach include factors related to ionization, ion/ion reactions, and mass analysis. This paper deals with issues regarding the ion polarity combination, viz., positive oligonucleotides/negative charge-transfer agent versus negative oligonucleotides/positive charge-transfer agent. Anions derived from perfluorocarbons appear to be directly applicable to mixtures of positive ions derived from electrospray of oligonucleotides, in direct analogy with positive protein ions. Conditions for forming positive oligonucleotide ions devoid of adducts were more difficult to establish than for forming relatively clean negative oligonucleotide ions. A new approach for manipulating negative ion charge states in the ion trap is described and is based on use of the electric field of the positive charge-transfer agent for storage of high-mass negative ions formed during the ion/ion reaction period. Oxygen cations are shown to be acceptable for charge-state manipulation of mixed-base oligomers but induce fragmentation in polyadenylate homopolymers. Protonated isobutylene (C4H9+), on the other hand, is shown to induce significantly less fragmentation of polyadenylate homopolymers.     

Performance evaluation of a hybrid linear ion trap/orbitrap mass spectrometer

Design and performance of a novel hybrid mass spectrometer is described. It couples a linear ion trap mass spectrometer to an orbitrap mass analyzer via an rf-only trapping quadrupole with a curved axis. The latter injects pulsed ion beams into a rapidly changing electric field in the orbitrap wherein they are trapped at high kinetic energies around an inner electrode. Image current detection is subsequently performed after a stable electrostatic field is achieved. Fourier transformation of the acquired transient allows wide mass range detection with high resolving power, mass accuracy, and dynamic range. The entire instrument operates in LC/MS mode (1 spectrum/s) with nominal mass resolving power of 60,000 and uses automatic gain control to provide high-accuracy mass measurements, within 2 ppm using internal standards and within 5 ppm with external calibration. The maximum resolving power exceeds 100,000 (fwhm). Rapid, automated data-dependent capabilities enable real-time acquisition of up to three high-mass accuracy MS/MS spectra per second.