Numerical Simulation Of The High Transportation Efficiency Ion Focusing Equipment

The sensitivity of ESI-MS is decided mainly by electrospray ionization rates and ion transport efficiency. Electrospray ionization can be effectively generated in atmospheric pressure and turning liquid analyte ions into gaseous ion through controlling the flow velocity, interface design, as well as the tube scabbard liquid analyte chemical processing. However, due to the ion beam caused by expansion coulombic space charge, the ion beam electrospray repulsion and sampling limit aperture features, only a small fraction (0.01-0.1%) of the electrospray ionization ions can enter the mass spectrum analyzer and finally be detected.In order to improve the ion transport efficiency between ESI ion source in atmospheric pressure and mass spectrometer orifice inlet in low pressure, a new electrospray ionization ion ion focusing lens device prototype has been developed in this paper. Based on the electrostatic dynamics'and flow dynamics'theory, ion transport efficiency could be significantly influented by applyling potentials on electrodes in order to forming a accumulation electrostatic field, as well as the utilization of high pressure disovation neutral gas.In order to improving ion transmission efficiency from atmospheric pressure MEMS ion sources to mass spectrometry, a novel ion focusing device has been developed and simulated by ANSYS software with finite element numerical method (FEM). The ion focusing device consists of two electrodes with progressively smaller internal diameter to which electric field are applied. Taguchi DOE has been used in the process of optimization of the structure and diameters of the device. Postprocessing will be implemented by Kriging interpolation method. The shapes of equipotential lines are measured to obtain the response for Taguchi DOE by CAD software. The significance of each factor and optimized structure has been obtained by signal-to-noise ratio and means variance analysis.Neutral gas flow simulation which assist gaseous ion of desolvation is performed by ANSYS/CFD FLOTRAN module. Variables used to form the flow field model are based on mean variance of electrostatic field analysis. This includes defination of flow field attribute, determination of the analysis parameters and the boundary conditions, usage of standard turbulent modelκ-εof compressible model analysis. The results shows that the velocity of neutral flow is supersonic which is the feature of a free-jet phenomenon, corresponding to the theoretical analysis and experimental observing.