Simulation And Optimization Of A Focusing Device For Electrospray Lonization

Electrospray ionization mass spectrometry (ESI-MS) technology has become an important tool for analysis, which is used in many fields, including large biological molecule. However, the ions transmission efficiency of typical mass spectrometry (MS) from ESI source to vacuum is only0.01-0.1%. Most of the ions are lost between the ESI source and MS. Only a fraction of ions can go through the MS inlet and be detected ultimately.In order to improve the ion transmission between the ESI source and MS, a novel ESI ion funnel is designed. Base on the theory of direct current (DC) field and radiofrequency (RF) field, the ion funnel uses a co-application of RF (two AC voltages with phase shift of180°) and DC electric fields to efficiently focus and transmit ions.A simulation has been done to analyze the effect of the electrodes on the ions focusing. A Taguchi Method has been used in the process of the structure optimization, which could reduce the number of the experiments and improve the simulation efficiency. After that, Kriging interpolation is selected to restore the equipotential lines in SURFER software. Finally the responses for Taguchi DOE are obtained in CAD. By analyzing the signal-to-noise ratio and means variance, the optimized structure parameters have been obtained.Base on the electrostatic field results, a novel ion funnels have been designed, and ion trajectory simulations have been done in COMSOL. Base on RF theory, a group of simulations have been done by changing the RF amplitudes and frequencies. In each simulation,37ion trajectories are plotted. Then the number of ions which could ultimately go through the MS inlet is selected as response.Finally, using LiveLinkTM for MATLAB, a user interface is created to allow geometry and physics parameterizations, and ion trajectories simulations to be conveniently performed, while the errors that may be caused by complex operations during the simulations are reduced. COMSOL provides a good and flexible platform for future simulations. By analysis of the simulation results, the optimized parameters are obtained to improve the overall ion transmission efficiency. These results give a good reference for the design and setup of the MEMS ion funnel.