Analytical approach for description of ion motion in quadrupole mass spectrometer

Abstract. The ion enhanced activation and collision-induced dissociation (CID) by simultaneous dipolar excitation of ions in the two radial directions of linear ion trap (LIT) have been recently developed and tested by experiment. In this work, its detailed properties were further studied by theoretical simulation. The effects of some experimental parameters such as the buffer gas pressure, the dipolar excitation signal phases, power amplitudes, and frequencies on the ion trajectory and energy were carefully investigated. The results show that the ion activation energy can be significantly increased by dual-direction excitation using two identical dipolar excitation signals because of the addition of an excitation dimension and the fact that the ion motion radius related to ion kinetic energy can be greater than the field radius. The effects of higher-order field components, such as dodecapole field on the performance of this method are also revealed. They mainly cause ion motion frequency shift as ion motion amplitude increases. Because of the frequency shift, there are different optimized excitation frequencies in different LITs. At the optimized frequency, ion average energy is improved significantly with relatively few ions lost. The results show that this method can be used in different kinds of LITs such as LIT with 4-fold symmetric stretch, linear quadrupole ion trap, and standard hyperbolic LIT, which can significantly increase the ion activation energy and CID efficiency, compared with the conventional method.

Section: Theoretical Methodsmentioning

confidence: 99%

Theoretical Study of Dual-Direction Dipolar Excitation of Ions in Linear Ion Traps

Dang

Wang

et al. 2016

“…As was demonstrated in [5], the P(a, q) function is useful for mapping of the stability boundaries where it is equal to zero. The value of P(a, q) is a real number only for a stable trajectory.…”

Section: Linear Quadrupolementioning

confidence: 99%

“…The value of P(a, q) is a real number only for a stable trajectory. The contour plot of the P(a, q) function values for the first stability region was depicted using x and y directions in [5]. Figure 1 represents the same for the second stability region.…”

Section: Linear Quadrupolementioning

confidence: 99%

“…The analytical method, in contrast to the matrix method, utilizes a single solution for a complete ion trajectory. The closed formulae obtained provide a general and preferable method for analytical expression of the fundamental properties of the quadrupole field such as ion trajectory stability, transmission/acceptance, resonance (see [5]), and momentum/energy characteristics of the ion motion. The linear quadrupole and the quadrupole trap are considered in this work as examples that demonstrate the advantages of the analytical method for the determination of the fundamental properties of the mass selecting devices as well as their effect on the ion energy.…”

mentioning

confidence: 99%

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Ion energy in quadrupole mass spectrometry

Baranov¹

2004

Application of an analytical solution of the Mathieu equation in conjunction with algebraic presentation of the Mathieu functions for description of the ion energy in a radiofrequency quadrupole field is discussed in this work. The analytical approach is used to express the ion energy averaged over the initial ion velocity distribution function, field phase and ion residence time. Comparisons with the approximate solutions for potential ion energy are presented with demonstration of their limits. Application of the method for different stability regions is discussed. Mathieu functions [1][2][3] has simplified theoretical description of the motion of ions in a quadrupole field. As a result of this progress, the algebraic aspects of the Mathieu functions were implemented "simply as another special function". The analytical method of the solution of the Mathieu equation in conjunction with algebraic presentation of the Mathieu functions allows introduction of simplifications and generalizations, delivering an alternative method to both the numerical solution of the Mathieu equation and to the matrix method. Previous attempts to use the Mathieu functions were too general due to the absence of simple algorithms or too local due to the necessity to use expansion series around small quantities (see [4] and references therein). The analytical method, in contrast to the matrix method, utilizes a single solution for a complete ion trajectory. The closed formulae obtained provide a general and preferable method for analytical expression of the fundamental properties of the quadrupole field such as ion trajectory stability, transmission/acceptance, resonance (see [5]), and momentum/energy characteristics of the ion motion. The linear quadrupole and the quadrupole trap are considered in this work as examples that demonstrate the advantages of the analytical method for the determination of the fundamental properties of the mass selecting devices as well as their effect on the ion energy. Illustrations of practical implementation of the method are also given for different regions of stability. In this work it is demonstrated that in order to evaluate the average ion energy in the quadrupole RF field, one has to calculate two dimensionless parameters 21 2 ͑a, q͒ and 22 2 ͑a, q͒, which depend only on the field properties. Linear QuadrupoleFor the two-dimensional quadrupole capacitor, the potential of the RF driven quadrupole field can be expressed as a combination of two terms having spatial (U) and periodic (V) trapping potentials:where r 0 is the electrode separation, is the main trapping RF angular frequency and is the initial phase of the main trapping frequency. In the vicinity of the z-axis, the electrostatic field of such a quadrupole has the equipotential lines forming a hyperbolic surface. That leads us to the system of equations for motion of an ion (with mass m and charge e) having arbitrary initial conditions {x i , y i , z i } and {ẋ i , ẏ i , ż i } (i-initial, t i ϭ 0) in Cartesian system of coordinates:Ά mẍ ͑t͒ ϭ ...

“…The average the radial ion energy E r in the presence of the RF field can be expressed as follows [14,15]:…”

Section: Influence Of the Rf Field On The Ion Energymentioning

confidence: 99%

The high-pressure segmented quadrupole collision cell (HP-SQCC) as an ion molecule reactor

Guo

Siu

Baranov³

2005

Self Cite

A high-pressure 20-segment quadrupole collision cell (HP-SQCC), which replaces a collision cell in a modified triple-quadrupole mass spectrometer is investigated in this work as an ion-molecule reactor with an inherent heat source. The highest working pressure achievable is 20 mTorr. The 20 quadrupole segments permit superimposition of linear axial electric field over the conventional quadrupole field in the radial direction. The axial and radial fields are employed to control ion temperature. Heat is transferred to the reactants through ion frictional heating. The HP-SQCC utilizes a combination of several physicochemical phenomena and an attempt is made to examine a range of ion-molecule reactions. Due to a sufficiently large number of reactive collisions, the reactor is used to promote sequential exothermic ion-molecule reactions. To characterize the performance of the HP-SQCC, the various ion-molecule reactions between the fragment ions of ferrocene ( on-molecule reactions have captured the fascination of mass spectrometrists for a number of decades and have been probed using a variety of instrumentation, including Fourier-transform ion cyclotron resonance spectrometry, ion-trap mass spectrometry, triplequadrupole mass spectrometry and the selected-ion flow tube technique [1]. The conventional triplequadrupole mass spectrometer is a less than perfect instrument for an examination of ion-molecule reactions due to the relatively low pressure achievable in its second quadrupole (Q 2 ), which restricts the number of ion-molecule collisions, and to the limited control of ion energy within Q 2 . Nevertheless, reactions that lead to novel products have been discovered; one such reaction is the ligand-exchange reaction between [Pb(CH 3 ; Pb 2ϩ had previously been described as to be among "a select group of doubly charged metal ions that will not form stable complexes in the gas phase with water" [3].Here we report the first ion-molecule reaction results obtained on a high-pressure 20-segment quadrupole collision cell (HP-SQCC) that functions as the Q 2 in a modified triple-quadrupole mass spectrometer. The highest working pressure achievable is 20 mTorr with neon, about 4 times higher than that achievable on a standard triple-quadrupole instrument. The 20 quadrupole segments permit superimposition of an axial electric field, typically linear, over the conventional quadrupole field in the radial direction [4][5][6]. The HP-SQCC was originally developed for ion-mobility measurements [5,7], where the goal is to maintain the drift field low enough that the ion temperature is not increased significantly. In this study, we are exploring the use of the HP-SQCC as an efficient apparatus for utilizing ion-molecule reactions as an analytical method. The axial and radial fields are employed to control the ion temperature.To characterize the performance of the HP-SQCC, we have elected to use as probes the various ionmolecule reactions between the fragment ions of ferrocene (Cp 2 Fe) as well as cobaltocene (Cp 2 Co) and neutra...