| The microwave plasma torch(MPT),which is generally recognized as an originality of Chinese scholars,is a milestone in the development of microwave plasma(MWP)sources.Since first introduced in 1985,MPT has gone through continuous developments and was widely used in various areas of spectrochemical analysis.However,the typical operating power of MPT maintained low(100?350 W)all the time,so it is difficult for direct introduction of wet sample aerosols.Low powered MPT spectrometers need to be coupled with various dry aerosol sample introduction techniques,such as electrothermal vaporization,desolvation system with heating and condensing units,and this is the main reason that the low powered MPT atomic emission spectrometer has not been widely accepted by the market.In this thesis,some improvements were applied to the traditional low powered MPT,a new MPT that can be operated with microwave power at kilowatt level was developed.The technology of self-ignition of the plasma was investigated,the application of the new MPT source was carried out,and a prototype of the sequential MPT spectrometer was developed.The main works and innovations of this thesis are listed as follows:(1).For the first time,the kilowatt MPT source which can operate steadily at microwave power at kilowatt level was developed,and this excitation source is suitable for atomic emission spectrochemical analysis with direct sample aerosol introduction.The main improvements include the optimization of coupling position and the study on heat sink when operating at kilowatt power.When working with argon,the plasma working at a few hundred watts behaves a single filament rotating to form a plasma with inverted funnel shape,and it turns to double filaments when microwave power goes up to kilowatt level.The analytical performance of the kilowatt MPT as an excitation source is much better than that of the traditional low powered MPT for most elements.(2).The ignition method of MPT was changed innovatively,and the self-ignition property of MPT was achieved.The resonance characters and the electric field distribution at the opening end of the torch were simulated by using simulation.Furthermore,with the inner tube protruding slightly out of the opening end of the torch,the electric field intensity at the plasma formation region is higher and thus the plasma could be self-ignited when the microwave power applied goes over 150 W.The achievement of self-ignition is of great importance,the construction of the instrument based on the MPT could be simplified,and its usability and reliability can be enhanced.It will be of great significance for the commercialization of MPT-based instruments.(3).For the first time,ArMPT atomic emission source was used in the detection of oil sample with direct atomization of diluted oil,and the strong tolerance to organic material of ArMPT was demonstrated.A sampling device used for on-line dilution of the oil sample introduced was developed.The analytical performance of the MPT excitation source with direct introduction of the diluted oil sample was tested.It shows the good prospect of application of MPT-AES in the field of determination of wear metal elements in oil.(4).MPT-AES working with helium for the detection of nonmetals was investigated.The powerful excitation ability of MPT working with helium to the ionic spectral lines of chlorine was verified.A vapor generation method was applied for the detection of chlorine in the sodium chloride solution,and the limit of detection for chlorine was 0.26 ?g·mL-1.(5).A prototype of spectrometer with sequential scanning based on MPT source working with microwave power at kilowatt level was developed.The performance was matched with the goal of the medium-term evaluation of the National Major Scientific Equipment Development Projects of China(Grant NO:2013YQ470781).The engineering resolution of the torch was considered throughout the process of the development,laying a good foundation for the commercialization of MPT spectrometer. |
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