Development Of Atmospheric Dielectric Barrier Discharge Ionization Sourceand Its Applicationin Miniaturized Mass Spectrometer

As the representative of modern high-end analytical instrument,mass spectrometer mainly obtains the information of composition and chemical structure of material by measuring the mass to charge ratio.It has been widely used in many fields such as space exploration,environmental testing,food safety testing and defense science and technology.As one of the core components of mass spectrometer,ionization source has developed rapidly in recent years.The direct ionization technique represented by atmospheric pressure desorption has become a research hotspot in the field of mass spectrometry.The technology has the advantages of in-situ,high-throughput,fast and real-time on-site detection.In this paper,based on the principle of dielectric barrier,an open atmospheric ion source has been developed with its simple structure,low ionization background noise and good reproducibility.A new technique of rapid evaporation-dielectric barrier discharge ionization is innovatively proposed,and several kinds of samples have been successfully detected by using a miniaturized mass spectrometer.The experimental results show that the technique has the merits of high sensitivity,good stability and good response.In the development of ionization source and the combined application of miniaturized mass spectrometer,the following achievements are mainly achieved:(1)Based on the principle of dielectric barrier discharge,the discharge structure with quartz tube as the dielectric barrier and "needle-ring" as the double electrode was designed.By optimizing the geometry size,the ionization efficiency is ensured and the carrier gas flow rate of the ionization source is reduced.The rapid evaporation heating platform is designed,with good thermal conductivity of aluminum as the substrate,the top of stainless steel 316L designed with low adsorption of the sample plate,the internal design of precision temperature control module,according to different samples to set the appropriate temperature,to ensure the maximum efficiency of sample introduction.(2)The paper independently designed,welded and debugged ionization source control circuit,wrote the rapid heating program based on the incremental PID control algorithm,completed the parameter setting by using the upper computer debugging interface,and realized the temperature control deviation within 0.1?.The flow rate control system based on mass flow controller MFC2022 is designed and built.According to the data transmission protocol,the helium flow rate control in the mode of keypad and wireless bluetooth is completed,and the control accuracy is less than 2%.Finally,the miniaturized dielectric barrier discharge ionization source can realize the function of plasma flame generation and sample ionization.(3)I participated in the installation of the mechanical part of the miniaturized mass spectrometer and independently completed the debugging of the electrical signal of the whole machine.In the process of the experiment,a number of parameters such as the sample temperature in the fast evaporation area,the helium flow rate,the vacuum degree in the ion funnel,and the inner diameter of the ion transmission line were optimized.The results showed that when the heating temperature was 170?,the helium flow rate was 400sccm,the inner diameter of the transmission rod was 0.38mm,and the vacuum degree in the ion funnel was about 3.0mbar,the sample detection effect was the best.Under the condition of selective ion storage,0.2ng/mL caffeine samples can be detected,which is nearly 10 times lower than the detection limit of conventional electrospray ionization source combined with miniaturized mass spectrometry.Compared with the dielectric barrier discharge ionization source without the aid of rapid evaporation,the caffeine signal detection strength of this experimental platform was increased by nearly 6 times.Through continuous sampling and collection of 200 mass spectrograms(the generation time of each spectrogram is less than 1s),the relative standard deviation(RSD)of sample ion strength is calculated to be 11.1%,and the results show that the stability of the platform is good.(4)A variety of samples including propofol,arginine,SIPI5286,reserpine,SIPI5358 and rhodamine B were tested by rapid evaporation-dielectric barrier discharge ionization.The results show that compared with the existing dielectric barrier discharge ionization sources on the market,the gas consumption of the ionization source independently developed in this paper is nearly 5 times less,the volume is smaller,and the detection and analysis effect can also be comparable.Finally,the ionization mechanism of dielectric barrier discharge ionization is discussed,and the proton transfer is verified,which indicates that water plays an important role in complex ionization reactions.