Performance Simulation of a Quadrupole Mass Filter Operating in the First and Third Stability Zones

We consider the case of a quadrupole mass spectrometer (QMS) in which a static magnetic field is applied axially in the z-direction along the length of the mass filter. The theoretical approach assumed in the model is that the QMS contains hyperbolic rods as electrodes and that the magnetic field acts over the full length of the mass filter assembly. Initial experimental results with argon and helium for a low-resolution instrument confirm the predicted theoretical trends. The analysis also predicts for which values of operating parameters an enhancement of the instrument resolution is achieved when an axial magnetic field is applied. The model predicts instrument resolution R Ͼ3000 for a QMS with a 200 mm long mass filter via application of an axial magnetic field. Attributes of the QMS such as versatility, accuracy, low cost, mass range, and sensitivity have ensured that it has been deployed in a wide range of applications, varying considerably from the modest residual gas analyzer to high-performance mass spectrometer for chemical analysis of simple and complex molecules, e.g., when used in conjunction with gas chromatography [7,8]. Different applications have different requirements for resolution, sensitivity, and stability.There have been many analytical predictions of the behavior of QMS. Dawson used matrix methods to calculate ion transmission for various scan lines and various apertures both with and without fringing fields, based on maximum ion displacements for mass filters [9]. Later research describes the performance of the QMS more comprehensively by solving the Mathieu equation in two dimensions for an infinitely long mass filter [2]. Batey showed that some features of the behavior of the QMS could be predicted by tracing the motion of ion through the mass filter [10]. Muntean used the matrix method to develop a computer simulation program to model ion transmission through the filter by calculating ion trajectories in radio frequency (rf) only quadrupoles [11]. More examples of such types of analytical work include the modeling of ion transmission through the filter by calculating ion trajectories in exactly determined hyperbolic quadrupole fields [12], the effects of rf frequency, phase and magnitude on the performance of QMS [13], and the effects of initial ion energy and quadrupole rod length on transmission percentage of ions through the mass filter along with the effects of aperture parameters [14]. Some workers have developed computational methods to determine the trajectories of large number of ions in QMS; their computer program generates large number of ions (at least 10 5 ions injected into the quadrupole model at each point on the mass scale), thus providing a detailed computer simulation for both hyperbolic and circular rods [15,16]. Douglas and Konenkov have used numerical calculations to investigate the influence of electrode radius r to field radius r 0 , which is referred to as (r/ r 0 ) on the peak shape for a linear QMF constructed with round rods [17]. Other workers have used com...

Section: F Irst Described By W Paul and H Steinwedel Inmentioning

confidence: 99%

Effect of an axial magnetic field on the performance of a quadrupole mass spectrometer

Syed

Sreekumar

Brkić

et al. 2010

“…Our numerical model may be used to produce individual mass peaks or complete mass spectrum and it can support any type of ion source together with QMF with electrodes of any profile. The model works by coupling the commercially available CPO3D program [23] with an in-house simulation program suite the QMS-2 [24].…”

Section: Modelingmentioning

confidence: 99%

“…It supports QMFs with hyperbolic, cylindrical, and square electrodes, giving accurate performance predictions [22,24,27], including the effect of electrode misalignment [28]. The purpose of the QMS-2 is to generate individual mass peaks and full mass spectra for given ion masses within a specified mass range for different stability zones.…”

Section: Modelingmentioning

confidence: 99%

Development of quadrupole mass spectrometers using rapid prototyping technology

Brkić

France

Clare

et al. 2009

In this report, we present a prototype design of a quadrupole mass filter (QMF) with hyperbolic electrodes, fabricated at the University of Liverpool using digital light processing (DLP), a low-cost and lightweight 3D rapid prototyping (RP) technique. Experimental mass spectra are shown for H 2 ϩ , D 2 ϩ , and He ϩ ions to provide proof of principle that the DLP mass filter is working as a mass analyzer in the low-mass range (1 to 10 amu). The performance of the DLP QMF has also been investigated for individual spectral peaks. Numerical simulations of the instrument were performed by coupling CPO and Liverpool QMS-2 programs to model both the ion source and mass filter, respectively, and the instrument is shown to perform as predicted by theory. DLP thus allows miniaturization of mass spectrometers at low cost, using hyperbolic (or other) geometries of mass analyzer electrodes that provide optimal ion manipulation and resolution for a given application. The potential of using RP fabrication techniques for developing miniature and microscale mass analyzers is also discussed. (J Am Soc Mass Spectrom 2009, 20, 1359 -1365

“…Du et al have performed elemental analysis with QMF operated in higher stability regions, and it was observed that there is an increase in resolution when QMF is operated in higher stability regions [16]. Hogan and Taylor performed computer simulation for a QMF operating in first and third stability zones, and it was concluded that operation in zone 3 provides an improved immunity from the effects of the variation in the value of electrode radius r to field radius r 0 (referred as r/r 0 ) compared with zone 1 [17].…”

Section: Introductionmentioning

confidence: 99%

Factors Influencing the QMF Resolution for Operation in Stability Zones 1 and 3

Syed

Hogan

Gibson

et al. 2012

This study uses a computer model to simulate a quadrupole mass filter (QMF) instrument under different operating conditions for Mathieu stability zones 1 and 3. The investigation considers the factors that limit the maximum resolution (R max ), which can be obtained for a given QMF for a particular value of scan line. Previously, QMF resolution (R) has been found to be dependent on number (N) of radio frequency (rf) cycles experienced by the ions in the mass filter, according to R=N n /K, where n and K are the constants. However, this expression does not predict the limit to QMF resolution observed in practice and is true only for the linear regions of the performance curve for QMF operation in zone 1 and zone 3 of the stability diagram. Here we model the saturated regions of the performance curve for QMF operation in zone 1 according to R=q(1 -2c N )/Δq, where c is a constant and Δq is the width of the intersection of the operating scan line with the stability zone 1, measured at q-axis of the Mathieu stability diagram. Also by careful calculations of the detail of the stability tip of zone 1, the following relationship was established between R max and percentage U/V ratio: R max =q/(0.9330-0.00933U/V). For QMF operation in zone 3 the expression R=a -bc N simulates well the linear and saturated regions of the performance curve for a range of operational conditions, where a, b, and c are constants.