| At present, electrospray ionization-quadrupole ion trap (ESI-QIT) Mass Spectrometer (MS) has been already widely applied in various fields, such as medicine analysis, proteomics and so on. With the rapid growth of demand for in-situ analysis, people become more and more interested in the development of miniature ESI-QIT MS. Development process of MS usually involves several steps. The development of mass analyzer is the first. After determining its performance meets the requirements, its components are developed. Finally, the integration of complete machine involves precise machineries, vacuum, electronic, software system and other technology, which is a complex task. In 2004, a new type of QIT mass analyzer - rectilinear ion trap (RIT) was reported by Ouyang and others in the United States Purdue University, which not only has advantage of large capacity ion and small mass discrimination, but also has relatively simple mechanical structure, was more suitable for the development of miniature MS. Two years later, they developed the world's smallest handheld electron ionization MS based on RIT. In 2006, Song and others of the United States Purdue University, who reported the two types of ESI-RIT MS, used commercial ESI-QIT MS components except RIT to keep the performance of instrument meeting parts of the demand for high-throughput research in the field of biology. In 2007, Jin Wei and others in Jilin University, who reported a ESI-RIT MS platform, mainly describes the development of mechanical components, and indicates that there are disparities in performance between domestic instruments and overseas. At present, the major problems in the research and development of ESI-RIT MS include parts of instruments'technology qualification lower than commercial ESI-QIT Mass Spectrometers', lake of research for the miniaturization of key components and short of theoretical and application research. With the support of the topic of the Key Technologies R&D Program of the National S&T Program in the 10th Five-year Plan in China, entitled as" Development of chromatograph-mass spectrometer", both the miniaturization technology of key components of digital control system and the effect of geometric error on quadrupole mass filter is researched, in addition, the higher mass resolution ESI-RIT MS is developed.(1)Development of miniature digital control system for QIT MSOwing to the operational principles of RIT and QIT MS are basically the same, the digital control system can be used in both of them. However, the traditional digital control system of QIT mass spectrometer has not already been able to meet the volume of QIT, especially the miniaturization trend of RIT mass spectrometer. Therefore, the two aspects of miniaturization technology are researched in the following.For the structure of the existing system is more complicated and the miniaturization of which is more difficult, a system structure based on a 32-bit micro-controller and the field programmable gate array without any digital signal processor is proposed. Hardware structure of the system includes the embedded motherboard, the control board and the weak current amplifier board. The embedded motherboard includes the 32-bit micro-controller, the ethernet interface, the simplified PC104 bus controller circuits, and the instrument control software on the remote computers to communicate with each other via Ethernet. The control board is used to be the PC104 bus interface board, whose core processor is a field programmable gate array, used to control the measurement & control circuit. The weak current amplifier board communications with the control board through low-voltage differential signals. The 32-bit micro-controller procedures are used to achieve data transmission and state detection, in addition, the field programmable gate array procedures are used to achieve the scanning timing and the control timing of circuit modules.According to the structure of the traditional control module for the resonant excitation is more complicated and the miniaturization of which is more difficult, methods to simplify the hardware circuit using the field programmable gate arrays software to achieve the wave amplitude modulation is proposed. The principle of this method is: the single-frequency signals are completed by the direct digital converter based on the software, and the amplitude modulation function is implemented by software multiplier, and the fast switch is achieved by a two-channel software switch. Due to the large-capacity field programmable gate array has been in the digital control system, the hardware of the resonant excitation control has only one digital-analog converter and one signal conditioning circuit, which simplifies the hardware structure and reduces the power consumption, compared to the traditional method using hardware to achieve the single-frequency signal, the amplitude modulation and the signal switching.The tests show that the volume of the miniature digital control system we developed is smaller than the other existing digital control system, and its performance and function could meet the needs of QIT MS.(2)Development of ESI-RIT MSThe RIT mechanical error has a greater impact on the mass resolution of equipments. There are many factors impacting the mechanical error in the previous assembly methods for RIT, so it is more difficult to reduce the mechanical error further.To solve this problem, the assembly method based on a high-precision dielectric slab and frock to reduce the RIT mechanical error is proposed, and a set of RIT ESI-RIT MS is developed.Principle of the new assembly methods: 4 pieces of self-made high-precision glass (or ceramics, and other dielectric material) are placed between RIT rf electrode pairs for the electrical isolation and to reduce the error between the x electrodes, and then a set of frock is also used to reduce the error between the y electrodes. The mechanical error of RIT we developed is less than 0.057 mm, and the previously reported one is 0.1 mm.ESI-RIT MS we developed includes the three-stage vacuum chamber, the Electrospray Ionization based on the double-layer atomization gas structure, the vacuum interface of atmospheric pressure ion source based on the structure of heating stainless steel capillary, the tubular ion lens designed for the ion focusing of the stainless steel capillary, the stainless steel skimmer electrode used to the extracted for the extraction of the ion beam from stainless steel capillary exit and the transmission to the second-stage vacuum chamber, the stainless steel square quadrupole and octopole used to transfer the ion from the Skimmer electrode to RIT. Through the analysis of the needs of performance, the domestic production of the low-power DC high-voltage module and the RF high-voltage module are used to drive the ion optical components.By the use of the small-scale digital control system researched in this paper and the instrument control software developed by NIM (National Institute of Metrology), the timing control of equipments and the human-computer interaction are realized.Finally, a set of ESI-RIT MS using the above-mentioned components has been developed. Tests show that the mass resolution of the equipment is better than the other existing ESI-RIT MS, the sensitivity, the stability and other qualification of which are close to parts of the commercial ESI-QIT MS overseas.(3)Effect of geometric error on mass resolution of QMF In the research, the influence of geometric error effect on the mass resolution of QIT is relatively poor. However, both the quadrupole mass filter and QIT has the same theoretical foundation, the research on quadrupole mass filter is relatively abundance, therefore, the correlative research of QIT is promoted, through studying the effect of geometric error on the performance of mass filter.To solve the inaccurate problem of the traditional calculating method, a numerical simulation method to calculate the effect of geometric error on the mass resolution of quadrupole mass filter is proposed.With the use of programs developed by Douglas and others to calculate, higher field distribution in different geometric error, as well as the data of the first stable region and mass spectrometry peak shape can be obtained. The analysis of it shows that the more geometric error, the greater the coefficient of higher field, and the geometric error makes the top of the first stable regions "circular", declining the mass resolution.Experimental contrasts: A quadrupole mass filter with the maximum geometric error of 5μm, has a resolution of 1000. In the condition, 3 geometric errors calculated by three methods in finding the resolution are respectively 350, 306, 2359, when we use numerical method to calculate, the resolution is 1178. Thus, the numerical results are closer to the real value.A miniature digital control system with the smaller size and the performance meeting the MS needs is manufactured. The ESI-RIT MS with the high mass resolution is also developed. The introduction of numerical simulation methods makes the calculation for the mass resolution of quadrupole mass filter more accurate.
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