Design And Development Of Drift Tube For Ion Mobility Spectrometry Of Triple Ultraviolet Lamp

Soil pollution has become one of the main problems of environmental pollution,and benzene series are the main source of soil pollutants.Therefore,real-time and rapid detection of benzene compounds in the soil is very important.Traditional detection techniques include gas chromatography(GC),liquid chromatography,and mass spectrometry.however,these methods have the disadvantages of complex and time-consuming pretreatment which causing its unsuitable for rapid in-situ online detection or outdoor monitoring.the emergence of ion mobility spectroscopy provides new possibilities for online monitoring.Ion mobility spectrometry(IMS)is a technique that uses different migration rates of charged ions in an electric field to separate the analyte.Compared with the above technologies,IMS has the advantages of high sensitivity,fast response time,low price,low manufacturing cost,and can be made into a portable instrument.In addition,the characteristics of the drift tube are the decisive factor for the performance of the IMS,and the high-performance drift tube will make the IMS have higher sensitivity and better resolution.Therefore,this thesis is mainly based on the drift tube for studying ion mobility spectroscopy and aims to design a drift tube with better performance to improve the performance of IMS for the detection of soil benzene series.The specific work and research results are as follows:(1)Designs and developments of IMS drift tube based on three-ultraviolet source have been systematically introduced,including simulation and design of ionization source,ion gate,Drift zone as well as the design of detector.First,a highly selective ionisation source of ultraviolet light has been selected;Second,in order to promote the utilization of substrate and ionizing effectiveness a cabin for three ultraviolet sources has been designed.Meanwhile,all parts of drift tube have been simulated via SIMION through which four results have been obtained.Applying a uniform electric field to ionization sources benefits the transition of ionized molecules;Uniform electric field in Drift zone can promote the sensitivity and resolution;Increasing thickness of insulation ring decreases the anti-interference capability in Drift zone which,however,can be improved by increasing outer diameter of Drift zone;Drift tube with high quality can be acquired through designs of both thin electrode and a thick electrode.It has shown that,by simulation of Bradbury-Nielsen gate ion gate via SIMION,short distance between ion gates improves the resolution but decreases the sensitivity.Finally,the design scheme of the drift tube in a three-ultraviolet-source IMS has been obtained according to the confirmation of sizes of different parts based on SIMION simulation and viability of mechanical machining.(2)The resolution and sensitivity influenced by both pulse width and electric field have been investigated and optimized.1)The experimental results that with the decrease of the pulse width,the resolution of IMS continues to increase while the sensitivity gradually decreases,which proves that the ion mobility spectrometer has an obvious discrimination effect.2)The electric field strength is directly proportional to the sensitivity.As the electric field strength increases,the sensitivity is on the rise.3)For the electronic field influence on the resolution,the results indicated there is an optimal electric field under gradually decreases,which proves that the ion mobility spectrometer has an obvious discrimination effect.2)The electric field strength is directly proportional to the sensitivity.As the electric field strength increases,the sensitivity is on the rise.3)For the electronic field influence on the resolution,the results indicated there is an optimal electric field under a pulse width,the optimal electric field varies under different pulse widths.4)Meanwhile,the flow velocity of both carrier gas and drift has been optimized by applying various flow velocities of carrier gas toward substrates.The optimal carrier gas flow rate is 0.2L/min,and the drift gas flow rate is 0.7L/min.Under optimized conditions,a standard sample of benzene was detected and the experimental measurement resolution was 57.(3)SIMION simulation was also performed on the Tyndal-Powell gate ion gate.The simulation found that increasing the voltage difference of the grid helps to increase the number of ions passing through.The main reason is that the increase in the gate voltage affects the width of the depletion region and the strength of the effective electric field.The decrease in the width of the depletion zone and the increase in the effective electric field strength are both conducive to ion compression,and ion compression will increase the number of passing ions,which is conducive to the improvement of the detection signal.At the same time,the research also found that the increase of the gate voltage difference will increase the sensitivity,and the improvement of the resolution can be achieved without increasing the pulse width.