The Study Of Fast Polarity Switching Ion Mobility Spectrometer Based On Corona Discharge Ionization

Ion mobility spectrometry was born in the 1970s and has become one of the main methods in the field of trace detection.Depending on the nature of the target molecule,positive or negative ions may be formed during the ionization process,while traditional ion mobility spectrometer can only work in a single mode of positive or negative polarity,and can only give detection results for one polarity of ions under the conditions of a single analysis,and cannot realize the simultaneous analysis of both positive and negative ions.This problem has been solved by two main methods:the use of a dual ion detector and polarity switching,respectively.The latter can reduce the size and cost of the hardware equipment compared to the dual ion detector approach,facilitating miniaturized design,and faster switching time can obtain more accurate detection results when the concentration of the analyte to be measured varies with time.This paper designs a fast polarity switching ion mobility spectrometry system based on corona ionization,whose fast polarity switching can effectively improve the accuracy of polarity switching IMS detection results,and the system is not subject to strict regulation and constraints compared with the instruments of radioactive ion sources.The main work includes the following points:(1)The system analysis of the polarity switching IMS was carried out,and the main factors affecting the polarity switching time were investigated;(2)The structural components of the fast polarity switching IMS were designed and optimized to reduce the influence of the migration tube parasitic capacitance on the switching time;(3)The circuit of the key parts of the fast polarity switching IMS was investigated,and innovative solutions were proposed in the design of the corona discharge ion source driver and isolated gate regulator circuit;(4)An experimental platform was built based on the above work,and a series of experiments were conducted to verify the results.The experimental results show that the optimization of the aperture grid regulator circuit design in this paper reduces the switching time of the polarity switching IMS to 3.3%of the original one,which is only 20 ms,and the detection performance of this polarity switching IMS is not affected by the polarity switching.The application study demonstrates the advantages of fast polarity switching for the detection of highly volatile substances.In addition to the individual detection of conventional drug and explosive samples,detection experiments were also conducted on mixed samples.It was not only confirmed that the polarity-switching ion mobility spectrometry platform can rapidly and accurately detect commnon drugs and explosives,but also demonstrated that it is fully capable of detecting positive and negative ions simultaneously.The limit of detection of positive and negative modes were characterized by Ketamine and TNT,respectively,and could reach 0.1 ng or even lower levels.