Research And Development Of Tandem Ion Trap In Space Mass Spectrometry Instrument With Mass Selective Ion Transfer And Accumulation

Development of science and technology has promoted human exploration to the microscopic world. The advantages of innovative mass spectrometer devices, such as high sensitivity, high resolution and rapid analysis, are becoming popular. Mass spectrometry(MS) instruments have been widely used in aerospace, life science, anti-terrorism, nuclear science, medicine, health, and environmental protection, and etc. The analysis capability of MS instruments is still powerless to large-scale or complex sample analysis. Therefore, the MS instruments combined with other purification or separation technologies have been widely adopted to improve analysis speed, such as GC/MS, LC/MS, CE/MS. The analysis performance of MS instruments still does not meet the application requirements. The technologies coupled with more mass analyzers are used to finish some hard work, which could not be progressed on a single mass analysis system. Besides, the usage could speed up analysis speed. To improve detection rate and reproducibility of low abundance targets in proteomics, single-cell metabonomics and other areas, this work explored the key technologies of quadrupole ion trap mass spectrometry instrument, and developed tandem ion trap in space mass spectrometry instrument with mass selective ion transfer and accumulation. It specifically includes the following:First, nonlinear ions motion characteristics were investigated in quadrupole ion trap. The main reason of ions nonlinear motion was analyzed by modeling of nonlinear motion caused by high-order fields(the electric field is not perfect) and space charge effect. Nonlinear motion equation was solved by harmonic balance method for the first time in the field of mass spectrometry as we known. Studies about the impacts of higher order fields and space charge on ion motion were performed. Based on the theoretical analysis of high order fields, a single ion excitation solution was designed. Simulation experiments’ results have shown that over ~90% efficiency of selective ion ejection can be achieved by using this solution, which could evidently improve the instrument sensitivity and the selective ion transfer efficiency of ion trap devices.Second, the present work developed a simulation software platform of quadrupole ion trap. The overall framework and control process of the simulation platform have been investigated by combining with ion trap theoretical models and application needs. The platform includes simulation method of electric fields, ion trajectory algorithm, reliable ion motion model, data analysis model. The effectiveness and reliability of the system was strongly supported by comparing the simulation results with actual experiments. The electric fields of three ion traps with different electrodes(hyperbolic electrode, circular electrode, and rectangular electrode) were simulated systematically on the platform. The performances of these ion traps were qualitatively analyzed on different electrode fabrication and assembly accuracy conditions. The results could be used as guidelines in design, fabrication and assembly process of new ion trap mass analyzer.Third, this work developed an ion trap mass spectrometry prototype. The prototype has three vacuum chambers, and it can contribute to sequence controls of 2-way RF signals, 2-way AC signals, 20-way DC signal, and 16-way switch. The prototype was designed with some expansion interfaces to support subsequent secondary development for satisfy experimental needs in the future. One or more of ion trap mass analyzers, which may be different types, can work well on the prototype. When the ion trap with circular electrodes is installed in the prototype, the mass resolution(FWHM) can achieve to ~5,000. This features strongly validated the stability and reliability of the prototype.Forth, this work explored the key development technologies of tandem ion trap in space instrument, designed three solutions, and performed the hardware experimental verifications of above two solutions.(1) 3D ion trap(CIT) and rectangular ion trap(RIT) in tandem: The advantages of the solution are high ejection efficiency on CIT, stronger trapping and larger ion storage capacities on RIT. Simulation experiments’ results have shown that, the offset voltage, buffer gas and injection hole locations greatly impacted on the performance of the solution. The highest efficiency of a single mass selective ion transfer(the percentage of ions count in RIT respect to ions count ejected from CIT) can achieve with ~40%.(2) ion trap with circular electrodes(LIT1) and ion trap with hyperbolic electrodes(LIT2) in tandem: the target ions in LIT1 are transported and accumulated to LIT2 by axial AC ejection in the solution. The hardware experimental results have shown that three times accumulative efficiency of mass selective ion transfer and accumulation is ~23.55%. Some advantages, such as stronger capacities in trapping and larger ion storage on LIT1 and high ejection efficiency on LIT2 were acquired.(3) ion trap with circular electrodes(LIT1) and ion trap with circular electrodes(LIT3) in tandem: LIT1 and LIT3 feature the same structure and size. In the solution, the first advantage is that the ions ejected from LIT1 have lower energy, and the second advantage is larger ion storage space on both LIT1 and LIT3, which could help to achieve the accumulation of a large number of target ions. This was further confirmed by simulation experiments. The target ions with higher energy are trapped due to the bigger size of LIT3. Actually, a better performance in improving the efficiency of mass selective ion transfer and accumulation was found in the hardware experiment. Three times accumulative efficiency of mass selective ion transfer and accumulation achieve with ~222.09 %.In summary, this work has investigated the ions nonlinear motion characteristics in ion trap, and developed a highly reliable ion trap software simulation platform after studying the theory of quadrupole ion trap mass analyzer. The tandem ion trap in space mass spectrometry instrument has been developed on foundation of theoretical analysis and simulation software platform. The mass selective ion transfer and accumulation based on mass spectrometry technologies is achieved, which could improve sample utilization and the analysis speed of mass spectrometry. This technology has great potential value in genomics research and large-scale sample analysis.