Numerical Study Of The Transport Efficiency Of Asymmetric Ion Funnels

Mass spectrometry,as a detection technique capable of measuring the mass of atomic molecules,is now widely used in various fields of scientific research.Ionization of atomic molecules and their transport in the mass spectrometer is a key technology to improve the detection limit of the device.In mass spectrometers,ion guidance devices are the key technology to enhance the efficiency of ion transport.The ion funnel scheme proposed at the end of last century can focus ions into ion beams with the smallest possible radius for transport,which greatly improves the efficiency of ion transport from atmospheric pressure environment to low vacuum environment.In this paper,we address several typical needs in current mass spectrometry applications,design a small ion funnel with reduced electrodes and reduced processing difficulties based on structural improvements,and develop several ion funnel structures with asymmetric properties to improve the transfer efficiency while solving the problem of the need for unbalanced enhancement in mass spectrometry transfer.The specific research contents and conclusions of this paper are as follows:First,a two-dimensional simulation platform is built using multi-physics field simulation software(COMSOL Multiphysics)to verify the accuracy of the constructed simulation model according to the ion funnel working principle.The small-volume ion funnel applied to miniaturized mass spectrometry was designed,and the influence of the inclination angle of the ion funnel on ion transport efficiency was studied,and the structure of the miniaturized ion funnel was determined.After numerical simulation,the number of electrodes can be reduced from 100 to 34 while ensuring the transfer efficiency,where the electrode thickness is 1 mm,the electrode spacing is 2mm,the tilt angle is tanα=0.40,and the total length of the whole ion funnel is 67 mm,which can be applied to the transfer of portable mass spectrometry.Secondly,the effects of RF frequency,RF voltage,DC electric field gradient,and background air pressure on ion transport characteristics are explored on the miniaturized structure.The RF frequency is 1.5MHz,the RF voltage amplitude is between 40～100V,the DC electric field gradient is between 21～25V/cm,and the background air pressure is in the range of 1～10Torr with the relatively best ion transport efficiency,which is close to 100% for ions with mass-to-charge ratio greater than 100 Da and up to 35% for ions with m/z=30Da.Finally,a 3D simulation platform was built on COMSOL Multiphysics to design a series of 3D ion funnel models with simple processing and assembly.A geometrically asymmetric spiral ion funnel structure was found to significantly improve the transport efficiency of low m/z ions,where the transport efficiency of m/z=30Da ions can be improved by 24.18%.It is also found that the transport efficiency improvement can be achieved by using ion funnels that are asymmetric in electrical parameters,and for the asymmetry of the DC electric field gradient,the transport efficiency of ions with m/z<50 Da is improved by more than 10%.