Experimental study on the acceptance of a quadrupole mass filter

The acceptance of a quadrupole mass filter is studied by means of a small alkali ion source movable under vacuum. Experimental results are in agreement with Dawson's theoretical calculations.     

Analysis of the quadrupole mass filter with quadrupole excitation by the envelope equation method

The method of the envelope equation has been developed to describe the stability of the motion of ions in a quadrupole mass filter in the presence of periodic excitations of the feeding voltage. Dynamic equations that describe the variations in the envelope of ion vibrations in the vicinity of the vertex of the first common stability region have been obtained and reduced to the form of the Mathieu equations. The splitting of the stability diagram of the motion of ions into stability islands due to excitation has been described. The results of the approximate theory have been confirmed by an exact analysis of the stability diagram for rational values of the relative excitation frequency. The boundaries of the applicability domain for the developed theory limited by first-order resonances have been determined.     

Simulation of ion-optical systems for mass spectrometers with a quadrupole mass filter

Ion-optical systems with intermediate focusing and parallel extraction of the ion beam are simulated. The systems may be integrated with a quadrupole mass filter in order to improve the analytical properties of the latter.     

Acceptance and transmission of a quadrupole mass filter with a prefilter

We have proposed an analytical model of a quadrupole mass filter with an additional rf quadrupole (prefilter) at its entry, which is based on the model of a transient field in the region between the edges of the mass filter electrodes and the prefilter electrodes. The characteristics of the complex mass filter have been investigated by the methods of phase space dynamics. In the presence of the entrance prefilter, instead of the entrance diaphragm, the y acceptance increases by 1.5 times relative to the x acceptance. Upon an increase in the ion residence time in the fringing field, the y acceptance contour exhibits the tendency to rotation on the phase plane, while the x acceptance contour is broadened in the x coordinate. The transmission function increases and oscillates upon an increase in the ion residence time in the fringing field. The result of numerical experiment using the SIMION 8 software differs from the result of analytical calculation by 14% for the x acceptance and by 35% for the y acceptance.     

Spatial harmonics of the field in a quadrupole mass filter with circular electrodes

The amplitudes of the spatial harmonics of the field are calculated for given displacements of the electrodes in a quadrupole mass filter relative to their optimum positions. The cases of radial and angular displacements of the electrodes, asymmetries in voltage supplied to the electrodes, and nonidentical rod diameters are considered. These data are required for calculating the actual shape of the mass peaks and will be useful in designing mass filters. Zh. Tekh. Fiz. 69, 96–101 (October 1999)     

Concept of the effective potential in describing the motion of ions in a quadrupole mass filter

We propose a generalization of the effective potential theory for the motion of particles in a rapidly oscillating electric field for the stability parameters lying near the boundary of the diagram where the standard effective potential theory is inapplicable. We derive the dynamic equations describing the variation of the envelope of ion oscillations for the motion of ions near the stability vertex of the first zone of the quadrupole mass filter. We reduce them to the form of the Hamilton equations for oscillations of a material particle in the field of potential forces. We obtain expressions for the effective potential well. It is shown that in spite of the high kinetic energy of oscillations, the depth of the effective potential well for ions in the quadrupole is less than 1 eV in the case of filtration with a mass resolution exceeding 200 units. The acceptance of the mass filter is calculated as a function of the stability parameters and the resolving power.     

A detailed study of the quadrupole mass filter operating with no d.c. component of the rods

A report is given of the results of an extensive series of measurements of the quadrupole mass spectrometer performance when operating in the retarding mode. It is shown that this mode has some significant advantages over conventional operation for the mass range 40–500 a.m.u. In particular, there is less dependence upon mechanical imperfections in the quadrupole lens assembly, with consequent improvement in long term stability. Also, because the analyser operates without any applied d.c. voltage, the defocussing action at its entrance is reduced and therefore mass discrimination reduced. Satellite peaks have been identified as arising from third- and fourth-order disturbances in the quadrupole field. Mapping the position of these satellites over the whole stability region helps the understanding of the effect of field imperfections.     

Acceptance of the quadrupole mass filter in the upper stability island under biharmonic excitation

Dynamic characteristics of the quadrupole mass filter (QMF) with the parametric resonance excitation of ion oscillations by a low additional HF voltage are studied by numerical methods. The upper stability island formed by instability bands that follow the isolines of stability parameters of the unperturbed first stability band is considered. Isolines of characteristic indices on the island’s parameter plane are calculated. Ion trajectories at characteristic points near the x and y island boundaries, which have the form of beats, are presented. Parameters of the ellipses are determined as functions of the initial phase at which the ions enter the HF field. These parameters are shown to be periodic with a period of π with respect to the phase shift between the main and additional HF voltages. As a result, the QMF acceptance and, consequently, transmittance have maxima as functions of the phase shift. Therefore, to increase the QMF transmittance, the biharmonic signal must be synchronized.     

Laser ablation of a silicon carbide target: a time-of-flight quadrupole mass spectrometric study

Laser ablation of a SiC target was attempted to investigate the formation mechanisms and expansion dynamics of ionic species including silicon carbide cluster ions in the plume. Time-of-arrival distributions of ions were analysed to obtain their mean velocities and spatial distributions. Laser-plume interaction was examined by illuminating the plume with a UV laser pulse. Si₂C was found to be the major photodissociation product of silicon carbide cluster ions. PACS 82.40.Ra; 79.20.Ds; 79.20.La     

Approximate calculation of the resolving power of a quadrupole mass filter as a function of the number of ion oscillations

The paper presents a theoretical solution to the investigated problem. The final relation is in qualitative agreement with that found experimentally in earlier papers; quantitatively, however, it gives a smaller number of ion oscillations in the quadrupole field for obtaining the necessary resolving power than does the experimental relation. Simultaneously, it points to the existence of other parameters influencing this dependence. It follows from a comparison of the theory and experiment that there probably exists another process not theoretically explained so far, which influences the experimental data.     

Homotopy analysis method for solving a couple of evolution equations and comparison with Adomian's decomposition method

In this paper, the homotopy analysis method is proposed to solve an evolution equation. Comparisons are made between the Adomian decomposition method (ADM), the exact solution and the proposed method. The results reveal that the proposed method is very effective and simple.     

A method for calculating adiabatic mass parameters: Application to isoscalar quadrupole modes in light nuclei

A method is given which reduces the evaluation of adiabatic inertial parameters to constrained Hartree-Fock calculations. Quadrupole masses are computed for some light nuclei. As a result of dynamical effects ¹²C is found to become oblate.     

Acceptance and transmittance of a quadrupole mass filter with amplitude modulation of RF voltage with allowance for an edge field

A method for calculating the acceptance of a quadrupole mass filter with amplitude modulation of rf voltage is developed. The key factor in determining the transformation of the phase ellipse by edge fields is taking into account the phase shift of the rf field during motion of ions in the input edge field. The variation of the combined acceptance depending on the axial energy of ions (or the transit time of ions through the edge field) is in conformity with the rated transmittance, which is an indirect indication of the correctness of the proposed approach.     

Homotopy analysis method for solving Abel differential equation of fractional order

In this study, the homotopy analysis method is used for solving the Abel differential equation with fractional order within the Caputo sense. Stabilityand convergence of the proposed approach is investigated. The numerical results demonstrate that the homotopy analysis method is accurate and readily implemented.     

Effect of an edge field on the acceptance of a quadrupole mass filter operating at the bottom vertex of the stability rectangle

A quadrupole mass filter (QMF) can operate with a large acceptance and high transmission at the bottom vertex S (a=2.5210, q=2.8153) of the stability quadrilateral. The combined acceptance at a level of 50% transmission and a resolving power of 100 equals 2.0×10⁻³ r ₀ ⁴ f ², which is comparable to the acceptance (5.1×10⁻³ r ₀ ⁴ f ²) of the standard operating regime of a QMF in the first stability region under the same computational conditions and optimal on-axis ion velocity. The acceptance is approximately three times higher in the presence of edge fields than in their absence. The optimal on-axis ion energy equals 1.15r ₀ f, where r ₀ is the radius of the field (the radius of the inscribed circle between the vertices of the electrodes) and f is the working frequency. In the gas-analysis regime a sensitivity of 10⁻⁵ A/Pa is achieved on a mass filter with rod length and rod diameter of 15 cm and 8 mm, respectively, frequency f=1 MHz, and field radius r ₀=0.35 cm. Zh. Tekh. Fiz. 67, 121–124 (October 1997)     

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介绍了为开展漏孔检测、氘-氦分辨性能及真空检漏技术等相关实验研究而进行的四极质谱计分析与测量系统的研制,描述了真空室结构、抽气设备的选型、测量仪器的选择及控制保护子系统工作方式。对系统进行了包括极限真空、残余气体质谱分析、漏放气率、质谱计性能等测试,结果表明本系统达到了设计要求。     

Theoretical possibilities of a solenoid as mass filter

The paper deals with equations of motion of ions in a time-dependent magnetic field of a solenoid. These lead to a Hill equation approximated by a Mathieu equation. The instability of solutions of these equations in certain regions implies a theoretical possibility of filtering ion beams according to masses.     

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利用一套四极质谱气体分析与测试系统,开展MicroVision Plus四极质谱计的氦(He)、氘(D2)分辨性能实验。分别向分析室送入He和D2,记录质谱图,得到质量刻度和分辨率等信息。He+峰位为(4.0022±0.0006)amu;D2+峰位为(4.0246±0.0006)amu。在10-6～10-4Pa的分压范围,观察到He和D2的分辨率随其分压强的增大而减小。在10-7Pa-m3-s-1的He漏孔条件下,调节D2送气量,He+/D2+分压峰值比在10-1量级可以分辨出He。     

Microfabricated quadrupole ion trap for mass spectrometer applications

An array of miniaturized cylindrical quadrupole ion traps, with a radius of 20 microm, is fabricated using silicon micromachining using phosphorus doped polysilicon and silicon dioxide for the purpose of creating a mass spectrometer on a chip. We have operated the array for mass-selective ion ejection and mass analysis using Xe ions at a pressure of 10(-4). The scaling rules for the ion trap in relation to operating pressure, voltage, and frequency are examined.