Computer Simulation of the Mass Filter for a Finite Length Quadrupole

✍ Scribed by J. J. Tunstall; A. C. C. Voo; S. Taylor

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 146 KB
• Volume: 11
• Category: Article
• ISSN: 0951-4198
• DOI: 10.1002/(sici)1097-0231(19970131)11:2<184::aid-rcm724>3.0.co;2-p

✦ Synopsis

The development of a computer program designed to simulate the performance of the mass filter in an ideal quadrupole mass spectrometer (QMS) is described. The simulation program provides flexible input parameters to allow the user to investigate the ion trajectories and transmission efficiency for different operating conditions. The program solves the Mathieu equation in two dimensions using a 4th-order Runge-Kutta iteration routine. the program is written in Turbo-Pascal and runs under DOS on any PC. The main original feature is the ability to simulate ion trajectories through the mass filter so as to study transmission efficiency for a finite length QMS under a range of operating conditions and for different design dimensions. The program has been used to analyse the change in QMS resolution with the number of RF cycles, DC voltage, ion energies, RF voltage magnitude and phase angle. The angle at which the ions enter the mass filter is significant and the effect of RF phase on transmission probability through the filter is critical. A comparison of the computer simulation with experimental results shows excellent agreement. The program also accurately predicts the long tail observed on the low mass side of the mass peaks.

A later version of the program incorporates Fourier series analysis to examine the effect of ion energies and entrance aperture for the mass filter for both sinusoidal RF excitation and RF with added harmonics. The addition of harmonics to the RF voltage reduces the instrument sensitivity compared with the sinusoidal case. However, for certain operating conditions, there is the possibility of operating the QMS with rectangular waveforms. This may be particularly advantageous when high frequency miniature quadrupoles are used.