Quadrupole Field Mass Analyzer Theoretical Research

Mass spectrometry provides high sensitivity for the analysis and identification of unknown compounds, and it has become one of the most widely used analytical technique in modern science. Mass spectrometry data is indispensable for many internationally recognized analytical standards. At the present time, mass spectrometer has become indispensable analytical instrument in many areas. Furthermore, mass spectrometer plays an increasingly important role in hot-spot fields such as drug discovery, life science, environmental protection, food safety. Determination of illicit drugs, public safety, aerospace and military technique, etc.For the more and more wildly use of the mass spectrometer, the requirements for mass spectrometers are becoming more and more large. In recent years, scientists started to research and develop new mass spectrometer or working modes. Quadrupole mass filter and quadrupole ion trap are two kinds of very important mass analyzers. Therefore, it is obvious very important to investigate quadrupole mass analyzers to improve their performances.Quadrupole mass filter and Quadrupole ion trap are two kinds of very important mass analyzers. These two mass analyzers separate ions according to the ratio mass/charge-number (m/z). Most of the investigation and separating of chemical or biochemical components could be done by proper using these two kinds of mass analyzers.Normally, the machining and assembly for mass analyzers is very complicated, which need great amounts of time and financing. Therefore it is quite necessary to optimize the parameters before facilitate the instrument. The simulation result offers great help for further experiment or manufacture of the mass analyzers.Recently, the simulation works for quadrupole mass analyzers, especially for quadrupole ion traps, are mainly based on how the structure of the mass analyzer effect multipole field coefficients, or how the structure of the mass analyzer effect the frequency of the mass trajectories, seldom any to investigate how the structure of the electrodes effect the performance of the instrument. However, the main porpose to do the simulation is to improve the performance of the mass analyzer.The main contributions of this dissertation for the degree of doctor of philosophy are listed followed:The study discussed here is mainly based on two mass analyzers taking advantages of 2D quadrupole electrode field, which are quadrupole mass filter and rectilinear ion trap. My study is to simulate the working process of the mass analyzers by computer in order to optimize the structure and to invent novel working modes.The simulation results are quite valueable and able to guide experiments.The main results of this dissertation are:(1)First of all, by changing the electrode structure of the quadrupole mass filter, the electrode fields inside the quadrpole mass filter is changed. In this way,by simulating the mass peaks under different conditions, the best electrode structure for the quadrupole mass filter is found to get the best performance.(2)Second of all, islands are created by auxiliary small RF voltage with low frequency in the stability diagram. In this way the mass peaks are improved for the edge of the stability diagram is sharped by those islands.(3)For quadrupole ion traps, first, we carried out a novel rectilinear ion trap. The surface conductor of each electrode plate is fabricated to several sections, and each section is added different RF voltages. So the field distributions inside the ion trap and the performance can be adjusted by changing either the RF powers on each section of the electrodes. Therefore by varying these parameters, we may optimize the performance of the field adjustable ion trap.Then, a novel ion trap mass analyzer with multiple ion trapping and analyzing channels is performed by computer simulation. The relationship between its geometry and performance is investigated and reported in this paper. By analyzing ion trajectories and calculate mass peaks by simulation, ITAs with better performance are separated with others. Both mass peak shape and ejection efficiency are taken into account. Some of the simulation results are compared with experimental data.(4)Two tandem quadrupole mass analyzers are discussed here. One is tandem RF-only quadrupole mass filter with quadrupolar excitation. The operation of RF only tandem mass filter based on the above property consists of two short rod sets, Ql and Q2. The first quadrupole Q1 with lower q value is used to reject higher mass ions and the second Q2 is operated as a lower mass filter with higher q value near the qo=0.9080 boundary.(5) A new method for rapid ion separation and transmission between linear ion traps. A novel mass-selected ion transmission method between ion traps was put forward. First, ions are trapped only in one of the traps by radio frequency mainly quadrupole field, while dipole excitations signal AC with 1/3 or other certain ratios frequency compared to RF signal was applied to the trap in which ions are trapped. By using of digital waveform techniques, an eject pulse can push or pull the excited ions out at appropriate time while leaving the other ions in the trap. The ions driven out the first ion trap are saved in the second trap by another retarding pulse. In this way, all the ions saved in the first ion trap can be used effectively and the efficiency of ion analysis is improved.The first chapter of this dissertation is the basic principles of quadrupole mass analyzers and background knowledge of quadrupole field simulations. Chapter two, three and four is to use quadrupole excitation to improve quadrupole mass filters. Chapter five, six and seven is to study rectilinear ion traps, inculding performance improvements and novel operation ways.In short, this dissertation optimized two kinds of mass analyzers, which operated in quadrupole fields. These two kinds of mass analyzers are quadrupole mass filters and rectilinear ion traps. This doctoral dissertation consists of eight parts and contents are summarized as follows:Chapter One:Introduction. This chapter outlines the basic principles of quadrupole mass filters and quadrupole ion traps, as well as simulation works done by others. This chapter points out the importance of simulation works in the development of quadrupole mass analyzers. Based on the summary of chapter one research presented in this paper and research ideas were made.Chapter Two:Mass peak shape improvement of a quadrupole mass filter when operating with rectangular wave power supply. Numeric experiments were performed to study the first and second stability regions and find the optimal configurations of a quadrupole mass filter constructed by the circular quadrupole rods with rectangular wave power supply. The ion transmission contours were calculated using ion trajectory simulations. For the first stability region, the optimal rod set configuration and the ratio r/r0 is 1.110-1.115; for the second stability region, it is 1.128-1.130. Low frequency DC modulation with the parameters of m=0.04-0.16 and v=ω/O=1/8-1/14 improves the mass peak shape of the circular rod quadrupole mass filter at the optimal r/r0 ratio of 1.130. The amplitude modulation does not improve mass peak shape.Chapter Three:Two stability islands near q=0.902 created by auxiliary RF vlotege. We report on numerical investigations of stability islands created by auxiliary RF voltage with high and low frequencies near q=0.902. Islands created by auxiliary RF voltage with low frequency v=1/10 is preferably in comparison with high frequency v=9/10. DC+RF separation mode is characterized with higher resolution R0.1=2000-3000 but required more separation time n=250. RF operation mode (a=0) allows resolution about R0.1=500-600 in cases both for v=1/10 and v=9/10 at a much shorter time which is n=50 RF cycles only.It was revealed that phase shift parameter a is an important parameter for adjusting maximum transmission. The period of transmission change with phase a equals to p/2 for RF separation mode and p for DC+RF operation mode.The transmission is strongly depends upon ion source parameters and to reach transmission 15% and resolution 3000, input ion beam with parameters are set to s x=0.015 and s v=0.001.Chapter Four:Tandem RF-only quadrupole mass filter with quadrupolar excitation. Auxiliary quadrupolar excitation by means of additional RF voltage with relatively lower amplitude and less frequency creates a powerful instability band in the interval of q=0-0.2 on the first stability diagram when a=0. And this instability band could be used to filter ions. Such RF only quadrupole mass filter (QMF) may be used as reject high mass filter for removing lower q ions with m=M0-8 mass range. The operation of RF only tandem mass filter based on the above property consists of two short rod sets,Q1 and Q2. The first quadrupole Q1 with lower q value is used to reject higher mass ions and the second Q2 is operated as a lower mass filter with higher q value near the q0=0.9080 boundary. For creating narrow Aq pass band near qo for mass filtration, the quadrupole excitation is also proposed to apply on Q2. It was shown that the resolution of R0.1=115O could be achieved when ions spend in quadrupole Q2 for only 40 RF cycles. Chapter Five:The simulation optimization for field adjustable ion trap. Here we carried out a novel rectilinear ion trap. The surface conductor of each electrode plate is fabricated to several sections, and each section is added different RF voltages. So the field distributions inside the ion trap and the performance can be adjusted by changing either the RF powers on each section of the electrodes. Therefore by varying these parameters, we may optimize the performance of the field adjustable ion trap.Chapter Six:The optimization for ion trap array (ITA) mass analyzer by computer simulation. Geometry optimization for Ion trap array (ITA) mass analyzer-a novel ion trap mass analyzer with multiple ion trapping and analyzing channels is performed by computer simulation. The relationship between its geometry and performance is investigated and reported in this paper. By analyzing ion trajectories and calculate mass peaks by simulation, ITAs with better performance are separated with others. Both mass peak shape and ejection efficiency are taken into account. Some of the simulation results are compared with experimental data.Chapter Seven:A new method for rapid ion separation and transmission between linear ion traps. A novel mass-selected ion transmission method between ion traps was put forward. First, ions are trapped only in one of the traps by radio frequency mainly quadrupole field, while dipole excitations signal AC with 1/3 or other certain ratios frequency compared to RF signal was applied to the trap in which ions are trapped. By using of digital waveform techniques, an eject pulse can push or pull the excited ions out at appropriate time while leaving the other ions in the trap. The ions driven out the first ion trap are saved in the second trap by another retarding pulse. In this way the certain m/z ions can be transmitted alone with others saved in the first trap.By using this method, up to 55% of ions with certain m/z can be eject out and saved in the second ion trap. This method can be applied under different q values. In this way, all the ions saved in the first ion trap can be used effectively and the efficiency of ion analysis is improved.Chapter Eight:Summary and Outlook. The achievements of this dissertation were concluded. Meanwhile, some drawbacks in our current researches were pointed out and the corresponding improvements were also presented.