Research On Ion Source Technology Of Mass Spectrometry Based On Electron Energy Scanning

In recent years,online detection and analysis technique has developed rapidly.It is widely used in the fields of food safety,environmental monitoring and industrial on-line detection.Among them,in the process of industrial on-line detection,the accurate detection of the type and content of process gas and tail gas in industrial production is of great significance to improve production efficiency and product quality.So the performance requirements for industrial on-line detection instruments are constantly improving.Compared with analytical instruments such as chromatography and spectrum,mass spectrometry has the advantages of real-time,broad spectrum and high sensitivity.Therefore,it has greater application potential in the field of industrial on-line detection.However,in on-line mass spectrometry,the traditional 70 e V electron bombardment ionization source makes too many fragment ions which cause the overlap of mass spectrometry peaks,resulting in a decrease in quantitative accuracy or even technical shortcomings that cannot be quantified.Thus,to some extent,this hinders its application in the industrial on-line field to some extent.In order to solve this problem,the following work is mainly carried out:（1）An on-line quadrupole mass spectrometer was developed.The instrument mainly included a vacuum system,an injection system,an ion source,a quadrupole mass analyzer,an ion detection device,a circuit measurement,a control system and a signal acquisition system.After the optimization and debugging of the relevant electrical parameters,the resolution of the whole machine is better than the unit resolution,the detection limit for benzene,toluene and so on is better than1 ppm,and the relative standard deviation of the total ion flow signal is less than1.6% through the 600-minute stability test of ambient air.（2）A composite ion source based on electron bombardment ionization source and single photon ionization source was designed and developed.The composite ion source shares the same ionization cavity,and two independent ionization modes an be selected to ionize separately according to the characteristics of the target gas and application requirements.The three-dimensional mechanical design software Solid Works and ion optical simulation software SIMION 8.0 were used to design the structure and optimize the electric field of the composite ion source.After completing the machining and ion source assembly,the composite ion source was installed on the above mass spectrometer,and the two low ionization energy modes of the composite ion source were tested respectively.Both the electron bombardment ionization source with low electron energy and the single photon ionization source can reduce or even eliminate the fragment ions,so that the molecular ion peaks can be directly characterized.（3）A gas quantitative detection method based on EI source electron energy scanning technique was developed,and the application test of the method was carried out by using the above mass spectrometry platform and composite ion source.By using the designed injection system,a variety of gas mixtures with different concentrations were produced for the study of this method.Firstly,the initial electron energy,stepping value and termination electron energy were determined according to the material composition of the mixed gas.Then,the electron energy was gradually scanned to the termination electron energy according to the stepping value.The signal intensity of fragment ions under each electron energy is recorded successively.Therefore,the relationship equations between the concentration to be calculated and the signal intensity were established,and then the concentration information was calculated through the equations.The method was applied to the quantitative detection of nitrogen and carbon dioxide,and the experimental results showed that the quantitative error of this method was less than 3.2%.