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Chemical Ionization Mass Spectrometry High-purity NO2+ Ion Source Research

Posted on:2018-04-11Degree:MasterType:Thesis
Country:ChinaCandidate:X B DuFull Text:PDF
GTID:2321330518475573Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Mass spectrometry (MS) has the advantages of high sensitivity, fast analysis, less sample consumption, has been widely used in environmental science, food science,medicine and other fields. The molecule ionization is one of the important part and key factor of MS; after years of development, there have been electron ionization, field ionization, field desorption ionization, chemical ionization and other ionization technique.Chemical ionization due to less fragment ions, analysis simple, high detection sensitivity,qualitative and quantitative measurement etc., have very important application of measuring in trace gas with high sensitivity. The chemical ionization mass spectrometry is gas molecules ionized by chemical reaction, so it is an important task that high-purity reactant ions research for different sample.In this paper, a method and a device for producing high purity NO2+ chemical ionization source are presented by means of the cascade of glow discharge and DBD. The research work on the high purity NO2+ chemical ionization mass spectrometry is described as follows:1. Design and optimization of 1 chemical ionization mass spectrometry of high purity N02+ ion source device structure. Through the selection of electrode materials on glow discharge, optimization of electrode diameter, thickness, produce stable ion current. By selecting the dielectric material and the electrode on the dielectric barrier of the reactor,optimize the discharge gap, the amplitude and frequency of excitation voltage, the dielectric barrier discharge reactor with low temperature plasma modification of N2/O2 mixture gas. Through the structure design and SIMION simulation produced ion beam energy and direction of ion flow. A high purity NO2+ chemical ionization mass spectrometer was constructed by combining the new ion source with an electrostatic ion transport part and a time-of-flight mass analyzer.2. To investigate the mechanism and influencing factors of chemical ionization mass spectrometry of high purity NO2+ ion source. The formation of high purity NO2+ was obtained on H3O+ which produced by water vapor discharge reacting with NOx/O3 which produced by N2/O2 mixture dielectric barrier discharge. The result show that there are many factors affecting the generation of high-purity NO2+ ionization source, including the ratio of mixture gas N2/O2, DBD reactor power, the intensity of glow discharge current,and the value of E/N in the drift tube. The research show that in the case of N2:O2=1:2,the average energy density at 4.5J/ml, the discharge current range from 0.4 mA to 0.8mA,and the E/N= 120?140Td, the ion source is capable of producing NO2+ with purity greater than 99%. The study also found the key factor for the formation of NO2+ was the concentration of NO2, O3 and H3O+.3. Application of chemical ionization mass spectrometry of high purity NO2+ ion source.The reaction of gas phase NO2+ and aromatic compounds show that it is a second order chemical reaction, and the product ions were similar, including [M-C]+, [M]+, [M+O]+,[M+NO2]+. The reaction rate constant measured in the experiment are the order of 10-9cm3/s.
Keywords/Search Tags:Chemical ionization mass spectrometry, Nitronium ion ?NO2+?, Dielectric barrier discharge, Glow discharge, Reaction rate constant
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