Research On On-line Gas Detection Technology Based On Low Energy Electron Impact Ionization Source Quadrupole Mass Spectrometry

With the continuous innovation of industrial technology,the requirement of on-line analysis instrument for industrial process on-line detection is getting higher and higher.Real-time,fast and accurate acquisition of characteristic parameters of reaction gas or tail gas in industrial production line is of great significance to process control and optimization of industrial production.On-line process mass spectrometry has the advantages of fast analysis speed,high sensitivity,strong versatility and good quality resolution in industrial on-line analysis technology.It has wide application in industrial on-line analysis.In process mass spectrometry,the traditional 70 eV electron impact ionization source will produce a large number of fragment ions,and the phenomenon of fragment ion peak superposition will cause inaccurate quantitative detection results.In order to improve the accuracy of on-line mass spectrometry in quantitative detection,a low-energy electron impact ionization source is needed for the ionization technology of on-line mass spectrometry.An on-line process quadrupole mass spectrometer was developed to overcome the shortcomings of traditional methods based on industrial on-line detection.The stable sampling system ensures the stability of the instrument signal.The double filament structure of the ionization source which can adjust the voltage at will is beneficial to the optimization of the electric field in the ionization chamber.The circuit system ensures the high-speed acquisition of the mass spectrometry signal.After debugging and optimization,the resolution of the instrument is better than the unit resolution.The detection limit of benzene and toluene reaches ppm.The relative standard deviation of the signal within 12 hours is less than 1.54%.In order to reduce the ionization efficiency of the electron impact ionization source after reducing the ionization energy,the structure of the ionization source was simulated and optimized.For the electron transmission hole of ionization source,a grid structure is designed and applied,which improves the electron utilization ratio of ionization source and the ionization efficiency of gas molecule is increased by 1.2-2 times.Aiming at the magnetic field of ionization source,the structure of ionization source magnet was simulated and optimized to improve the beam current ability of magnetic field to electrons and ions,and the structure of large magnet with magnetic conductivity material was designed.By optimizing the structure of the ionization source,the ionization efficiency of the ionization source is improved,and the low energy electron impact ionization has a broader application space.The on-line process low energy electron impact ionization quadrupole mass spectrometry is applied to the quantitative detection of simulated gases in fermentation tail gas.According to the composition of gases,a set of methods of electronic energy selection is developed.Then the relationship among filament emission current,electronic energy and electron receiving electrode voltage is experimented,and three optimization schemes of instrument parameters are obtained to reduce the space charge effect.Improve the sensitivity of the instrument.Under the optimized low energy electron impact ionization mode,the gas fragment ions decrease and the molecular ion peaks increase.The linearity of carbon dioxide is good in the range of 0.03%~8% volume fraction,the correlation coefficient is 0.99986,the relative standard deviation of signal is less than 5%,and the minimum detection limit is 0.023%.