Research On Ion Operation Mode In Quadrupole Field At Low Vacuum

With the rapid development of the mass spectrometry technology, the mass spectrometers play a more and more important role in our daily life. Although the high performance, most of them must be operated at high vacuum condition, with large volume, heavy weight and high power consumption. Besides they can’t be taken for real-time analysis at ease. In this paper, the two-dimensional linear ion trap is selected for studying the operation mode of charged ions in ideal quadrupole field at low vacuum.Firstly, the simulation software SIMION is introduced in brief, then the basic law of charged ions in ideal quadrupole field at high vacuum is introduced theoretically, including Mathieu equation, the stable region of ion motion, the secular frequency and so on.Secondly, two kinds of common elastic collision models between charged ions and inert gas are mentioned, namely the Langevin model and Hardsphere model. By simulation and comparison, the appropriate model is chosen; the amendment of Mathieu equation is fulfilled by adding a damping term, the stable region at low vacuum is calculated in mathematical way.Finally, several standards for mass spectrometer performance evaluation are referred in detail, and also the three important steps for the whole mass analysis and two kinds of ions ejection methods, then the classic operation mode is given; by modeling and simulation with SIMION, the influence on the resolution caused by different parameters are considered, such as the cooling time, the amplitude and frequency of auxiliary AC. At last, the parameters of ion operation model at low vacuum are obtained.On the basic of meeting performance requirements, this research can simplify the vacuum system of the mass spectrometer, which leads to the decrease of the instrument volume, weight and power consumption, and also conforms to the trend of miniaturization of mass spectrometers.