Research On Construction And Application Of Atmospheric Pressure Glow Discharge Microplasma Device

Element quantitative analysis method is a necessary means for human to obtain theinformation of material composition.The detection environment support,high-power power supply and a large amount of high-purity argon or acetylene in the detection process of traditional analytical methods(such as optical emission spectrometry or mass spectrometry)are the key factors restricting the development of existing analytical methods to simple,fast and low-cost on-line analysis.Atmospheric pressure glow discharge(APGD)is a kind of gas discharge phenomenon that can produce plasma with millimeter scale or even lower in atmospheric environment.Most importantly,atomization,excitation and even ionization of elements can be achieved with APGD.However,the limited discharge energy density of APGD plasma and the unclear discharge mechanism directly restrict the detection sensitivity and accuracy of APGD when it is applied to element determination.Therefore,in this dissertation,the APGD structure was reconstructed based on the existing cognition of discharge mechanism to increase its discharge energy density,thereby increasing the excitation efficiency of the elements.Besides,APGD plasma was applied to in-situ analysis of solid samples by using molten salt as melt electrode.And with the help of Shanghai synchrotron radiation source technology,the research on APGD discharge mechanism was further deepened.The main research contents and results are described as follows:(1)Improvement and verification of APGD discharge energy density:Based on the physical means of space constraint,the APGD discharge structure was redesigned and the space-constrained APGD system was constructed.The higher negative dynamic resistance and the smaller plasma coverage area on the electrode surface during the discharge process indicated that the energy density of the discharge plasma is significantly improved.The structure of reconstructed APGD system allowed the collection of optical radiation signals along the axis of the discharge plasma,which can ensure the efficient collection of plasma emission spectrometry with the optimized distance between the plasma and the optical emission spectrometry system.Most importantly,the plasma produced by discharge in H₂-He atmosphere has satisfactory spectral performance(low spectral interference),which provided an important technical support for APGD as a radiation source in element detection.(2)Research on application of space-constrained APGD discharge system:Based on the gas nozzle jet electrode of space-constrained APGD system,the hydride generation system(HG)was successfully coupled to the cathode of space-constrained APGD.By systematically optimizing the key experimental parameters of Hg and APGD system,the developed system achieved Se and As detection limits of 0.087 and0.13 ng?m L^-1,respectively,with the corresponding relative standard deviations at analyte concentrations of 50 ng?m L^-1 being<0.5%in both cases.Moreover,the detection system was advantageous in that it exhibited a low power consumption(<17W)and a low gas consumption(<100 m L?min^-1).The recoveries of Se and As obtained at both foreign ion(Al³⁺?Co²⁺?Fe²⁺?Mg²⁺?Na⁺?Ni²⁺and Zn²⁺)concentrations of 10 and 50 mg?L^-1 were in the range of 90-105%,which indicated that the system proposed in present work had satisfactory performance in the anti-interference ability.The detection linear range can reach three orders of magnitude,and the analytical performance for As and Se can reach or even surpass that of conventional analytical instruments.The method has been applied to the determination of scallop certified reference material(GBW10024)and real mouse blood samples with satisfactory accuracy.(3)Construction of molten salt-metal electrode APGD system and its application in in-situ analysis of solid sample:By using molten salt as the melt electrode of APGD system and shortening the electrode spacing,a stable discharge plasma was ignited and maintained between the molten salt(Zn Cl₂ or KCl-Li Cl salt)electrode and the metal electrode.The negative dynamic resistance of discharge indicated that the discharge operated in the normal mode.The resulting of applying molten salt-metal electrode APGD system as radiation source indicated that the in-situ excitation of elements in solid salt samples(Zn Cl₂ and KCl-Li Cl molten salt)and conductive solid metal materials can be achieved with APGD system.And the relatively high emission sensitivity and precision with optimized experimental parameters indicated that molten salt-metal electrode APGD system can provide technical ideas for the application of APGD plasma in solid in-situ analysis.(4)Research on discharge mechanism of atmospheric solution cathode glow discharge based on Shanghai Synchrotron Radiation Facility(SSRF)imaging technology:The solution cathode glow discharge(SCGD)system was reconstructed,which ensured that the plasma can be ignited automatically and the discharge state can be controlled in real time outside the optical shed with the help of the electronically controlled translation stage.Based on the reconstructed SCGD system,the Shanghai Synchrotron Radiation Facility BL09B beamline was successfully used to perform high-time-resolution imaging of the ignition process of discharge and the plasma generated.The imaging results showed that a large number of droplets were generated in the SCGD discharge process and entered into the plasma.Meanwhile,the arc-shaped surface of the solution cathode expanded outward due to the electric field force during the ignition of discharge.The above findings further verified the possibility of a process similar to the electrospray discharge mechanism in SCGD discharge.However,due to the limited ability of characterization technology and the low density of SCGD discharge plasma,a lot of scientific research is necessary before the complex discharge mechanism in SCGD is proposed.