The High Sensitivity Experimental Analysis Of Trace Impurities With Quadrupole Mass Spectrometer In The Vacuum Environment

Trace gas analysis is very important and has been widely used in the field of environmental protection, biological technology, semiconductor technology, medicine and space technology. Therefore, the accurate and effective measurement of trace gases in the vacuum environment has the extremely vital significance.Several methods of the composition of trace impurity gas and methods of gas pre-concentration in the vacuum environment are introduced and contrasted in this paper, including gas chromatography, spectrometry, quadrupole mass spectrometry, pressure concentration method, solvent extraction method, getter method and condensation method. The quadrupole mass spectrometry has the advantages of simple equipment, high sensitivity, good qualitative, fast analysis speed. The condensation method has the advantages of simple operation, samples without pretreatment and can be used online. Therefore, in order to improve the sensitivity of the quadrupole mass spectrometer, the condensation enrichment method combined with the quadrupole mass spectrometer is used to measure the amount of the trace impurities in the vacuum system in this paper.The preliminary theoretical analysis of the condensation enrichment process to improve the sensitivity of the quadrupole mass spectrometry method is completed in this paper. The structure of adjustable concentrator is designed and connected with the dynamin vacuum system in this paper. The performance of the structure is studied experimentally. The experimental results show that the ultimate pressure of vacuum system after baking 48 hours is 1×10-6Pa.The trace impurities is analyzed in the vacuum system and single gas by the condensation enrichment method, and then the condensation effect of different cooling time is compared. The experimental results show that after condensing enrichment, the gas mass spectrum peak of CH4, H2O and CO increases significantly in the vacuum system without baking and after baking, and 25 minutes is best. The same mass spectrum peak increases in the gas sample of air,methane and Ar. When the main gas is Ar, the content of CH4, H2O and CO change from 4.63‰,3.81‰,5.41‰ to 7.01‰,7.32‰ and 7.52‰. The sensitivity increases much more when adding the Nanofiber-based enrichment device.The calculation results show that the condensation method in improving the sensitivity of the quadrupole mass spectrometry method is effective. The formula of condensation coefficient of specific gas is fit out. The theoretical value and experimental value of CH4 and H2O are compared in different pressure,and the result shows that the error is within the permitted scope.