Performance Optimization Of Half Round Rod Electrode Linear Ion Trap

In the mass spectrometry system,mass analyser affects the analysis performance of the whole system.Featured with simple structure,low vacuum requirement,and achievable multi-stage tandem mass spectrometry,the ion trap mass analyser is the most extensively applied among numerous mass analysers.However,its shortcomings like difficult processing of linear ion trap,low precision and inconvenient installation of the traditional hyperboloid have greatly limited its development to a certain extent.Therefore,this paper proposes a half round rod electrodes linear ion trap(HreLIT),though its analysis performance declines substantially compared with the traditional hyperboloid linear ion trap.The analysis performance of ion trap is mainly influenced by its internal electric field which is usually determined by the electrode structure and geometric size.Hence,to improve the analysis performance of HreLIT,this paper adopts two optimization methods for electrode structure based on the research of previous scholars,which are(1)optimizing the ratio of electrode radius in ion trap to the field radius(r/r0);and(2)optimizing the"stretching" distance of electrode in the emitting direction of ion trap,respectively.The essence of both methods is to change the internal electric field through optimizing the geometric size,so as to enhance its analysis performance.Regarding the research approaches,this study employs the method combining theoretical analogue,simulation,and experimental verification.Firstly,through methods like geometric modelling,electric field analysis and ion movement track simulation,this paper analyses and assesses the performance of HreLIT with different sizes.The specific simulation process is as below.First of all,the HreLIT model with different r/r0 and"stretching" distances is established via SIMION software to analyze the internal electric field distribution.Subsequently,the internal ion movement tracks of ion trap in different sizes are simulated through AXISM software,so as to acquire the simulation spectrometry figures.By comparing the peak shapes and mass resolution of spectrometry peaks,the performance of HreLIT with different geometric structures is analysed.Finally,based on the theoretical simulation,the geometric models with excellent simulation results are selected,and the HreLIT is processed and manufactured.In addition,the mass spectrometry system is established to implement the practical analysis experiment to verify the simulation results of this paper.Through software simulation,it is observed that the ratio of electrode radius to field radius(r/r0)is between 1.08(5/4.6)to 1.25(5/4),By regulating the "stretching" distance,high mass resolution can be achieved.When the scanning rate is 1600amu/s,the mass resolution can reach over 3000.Consequently,combining the simulation results with practical experience,this paper selects r/r0=5/4,and the "stretching" distances of 1.0mm and 1.4mm to make experimental verification.As the experimental results reveal,when the scanning rate is 1800amu/s,the ion mass resolution with mass-to-charge ratio of 609Da is 1603;when the scanning rate is 323 amu/s,it can reach 4060.Compared with the original size,the optimized HreLIT has greatly improved in key performance indicators,such as mass resolution.Hence,this paper is of significant guiding importance to the design and application of HreLIT-oriented mass spectrometry system.