Study On The Mechanism Of Ionization Of Samples By Dielectric Barrier Discharge Ion Source (DBDI)

Ambient mass spectrometry ion sources have been widely concerned in recent years because of its outstanding features,including rapid,in situ,real-time ionization of sample,which has become a research hotspot of mass spectrometric analysis.Dielectric barrier discharge ionization?DBDI?is proposed by Professor Zhang Xinrong in Tsinghua University for the first time in 2007,which can utilize the AC high voltage discharge under the condition of dielectric barrier discharge and excite inert gases such as helium to generate the plasma for ionization in the direct analysis of analytes.DBDI has become a hot research topic in ambient ion source for its advantages,e.g.,auxiliary solvent-free method,use at atmospheric pressure,a wide range of applications and easy miniaturization.BDI ionization mechanism is much complicated,although a lot of researches have been carried out on the ionization mechanism by domestic and foreign scholars,but there are still shortcomings.For example,the effect of different particles on the ionization process of the target compounds is not yet clear,because the particle composition in the plasma is very complex.Although the effect of water vapor on the ionization process is promoted,the effect of humidity and different?H₂O?_nH⁺ on the ionization process is unclear.Although the heating samples can promote the desorption process and improve the ionization efficiency,there are few researches on the heating of the ionized gas.This paper takes into research from the following four parts according to the above problem.Firstly,the structure principle of the single electrode DBDI ion source is elaborated,because of the analysis of the electric field characteristics and the length of plasma beam of the three electrode structures commonly used in the dielectric barrier discharge ion source,and the subsequent experiments are carried out based on the ion source.Secondly,the emission spectra of helium and argon plasma is studied by means of plasma emission spectroscopy.The composition of the plasma and the reaction mechanism between the particles are described in detail with the mass spectra of the actual samples.The results show that the DBDI ionization mechanism is similar to the DART transient micro-environment mechanism,but there is still much different;Thirdly,the ionization effect on the humidity in the ionization zone and different?H₂O?_nH⁺ is studied by the method of adding water vapor in the ionized region and introducing water vapor into the helium.The results show that the mixture of helium and water vapor can improve the signal strength and SNR.Finally,the effect of heating on the plasma and different melting point samples is studied by the method of heating helium.The results show that the heating can increase the length of the plasma beam,and the melting point of the sample is positively correlated with the optimum detection temperature.Therefore,the study of DBDI ionization mechanism can provide a basis for further optimizing the performance of ion source and improving ionization efficiency,which can provide scientific theoretical basis for future application researches and have important theoretical significance s for future development in other fields.