The Application Of Thermal Desorption Mass Spectrometry In The Analysis Of Surface Contaminants

The materials used in the vacuum system, because of the process of processing, cleaning, assembling and operating, are contaminanted by organic compounds on the surface. These contaminants will be released again under certain conditions and then float or deposit on the surface of the vacuum chamber and other optical components. They will lead to system contamination, component degradation and other negative effects. Therefore, the detection and analysis of surface contamination is very important.Several common surface contaminant analysis methods and mass spectrometry atmospheric pressure ionization techniques are introduced and contrasted in this paper, including chromatography, spectrometry, mass spectrometry, spray ionization technology, discharge ionization technology, laser assisted desorption ionization and thermal desorption ionization technology. The mass spectrometry has the advantages of simple equipment, high sensitivity, good qualitative capacity, fast analysis speed. Thermal desorption ionization has a small heating apparatus which is simple and easy to carry, and it use bellows to connect mass spectrometer and inlet, as a result, it is convenient for online analysis. Therefore, the thermal desorption mass spectrometry is used to analysis surface contaminants.Firstly, the basic principle of thermal desorption mass spectrometry is introduced, according to the basic principle, two restricted factors of sampling efficiency are discussed, the desorption temperature and parameters of sampling device. The analysis of desorption temperature show that desorption temperature increases as heating power increases, desorption temperature increases as flow rate increases, but sampling efficiency decreases as rate increases. The simulation study of sampling device show that sampling efficiency is higher when the injection angle of gas is about 20°?30°, sampling efficiency increases as vacuum inlet's height decreases, sampling efficiency is higher when the diameter of vacuum inlet is 0.8mm and the size of the gap is 0.5mm.The restricted factors of thermal desorption mass spectrometry's analysis sensitivity is analyzed. The results show that analysis sensitivity increases as heating power increases, analysis sensitivity decreases as flow rate increases, analysis sensitivity is higher when the injection angle of gas is about 20°, analysis sensitivity increases as vacuum inlet's height decreases, analysis sensitivity is higher when the size of the gap is 0.7mm, analysis sensitivity increases as the thermal conductivity of the material surface becomes better for the same contaminants.The theory and device of condensation enrichment and nano fiber enrichment device is introduced. The impact of condensation enrichment and enrichment in condensing device on analysis sensitivity are researched. Solid sample, liquid sample by smear collection, liquid sample by evaporation collection and the sample after cleaning are analyzed. The results show that it can greatly improve the sensitivity of analysis after condensation enrichment and place enrichment in the condensing device.