Development Of A Small High Voltage Discharge Ion Source And Its Application In Ambient Mass Spectrometry

Mass spectrometry is mainly used to obtain mass information by measuring the mass-to-charge ratio of analytes.This technique is now widely used in the fields of environment,food,medicine,forensics and biomedicine.Ambient ionization mass spectrometry（AIMS）is a much recent mass spectrometry technique by using an ambient ion source.AIMS has been developed rapidly in recent years and has become one of the hot spots in the research field of mass spectrometry.AIMS has various advantages such as fast-operation,real-time,high throughput,and no requirement of complicated sample pretreatment process.In this thesis,a pulsed high-voltage discharge device with the function of generating low-temperature plasma was selected to build an ambient ion source with the advantages of simple device assambly,easy operation,high response value and good reproducibility.This ion source is coupled with a quadrupole time-of-flight mass spectrometer to detect a wide range of anlytes from different samples.The results of this thesis show that the established AIMS method has advantages of high sensitivity,low detection limit and good stability.（1）In this thesis,firstly,three different types of small discharge devices were selected to evaluate,where cyclohexane was used as the sample.By comparing the signal intensity values of cyclohexane,the pulsed high-voltage discharge device with high signal intensity and good stability was finally selected as the ion source.In order to improve the desorption efficiency of analytes from the sample,a home-made temperature-controlled gas heating device was designed and fabricated,either.（2）The distance between the ion source and the mass spectrometer,the distance between the heating gas device and the ion source,and the auxiliary gas flow rate were optimized.The configuration of the ion source was optimized with a distance of 2.5 cm between the ion source and the mass spectrometer,a distance of 3.0 cm between the heating gas device and the ion source,and an auxiliary gas flow rate of 10 L/min and a temperature setting of 25℃.（3）Using the constructed pulsed high-pressure discharge ionization time-of-flight mass spectrometry,the direct analysis of various substances,including polymethoxyflavones,chrysophanes,serpentine,methamphetamine,bisphenol S（BPS）and ibuprofen in orange peel,were achieved with the detection limit of BPS of 2.39×10^-6 mol/L with a spiked recovery of104.56%,the detection limit of ibuprofen of 4.26×10^-8 mol/L with the spiked recovery of 96%and the limit of detection of nicotine of 1.59×10^-9 mol/L.（4）When the pulsed high-pressure discharge ionization time-of-flight mass spectrometry was applied to detect the content of nicotine in human breath after smoking,both accurate and reliable results were obtained.The pulsed high-pressure discharge ionization time-of-flight mass spectrometry established in this thesis has the characteristics of rapid,direct analysis,in situ analysis and convenience,which can be widely applied to the metabolic study of volatile small molecules in human body and has strong potential for application in clinical diagnosis.