Simulation of Absolute Mobility Ionic Migration in Non-Aqueous Capillary Zone Electrophoresis
Ming-Ying Hsu and Chen-I Hung
Traditional numerical schemes use the concentration diffusion equation to simulate the solute concentration distribution in CZE (Capillary Zone Electrophoresis) systems. However, although this equation adequately describes the diffusion of a solute liquid in such systems, it cannot describe the different motions of the differently charged solute ions. Therefore, this study employs a particle model to simulate solute ionic migration. Using the Navier-Stokes equation and the PIC (Particle in Cell) method, this study examines the absolute mobility of negatively and positively charged ions in non-aqueous solvents in cross-type and double T-type form CZE system. The reduction in the electroosmotic velocity caused by the geometry change as the injected flow exits the injection channel and enters the separation section region of the microchannel is quantified using a geometry factor, α, defined as the ratio of the electroosmotic velocity in the cross region of the microchannel to that in the injection channel. Furthermore, the study introduces an ionic migration factor, γ, to relate the electroosmotic velocity and electrophoresis velocity of the charged ions. Simulations are performed at various values of the ionic migration factor and Reynolds number to determine the operating conditions which ensure that both the negatively charged ions and the positively charged ions can migrate into the separation section of the microchannel for subsequent detection in the downstream region of the separation channel. The numerical approach proposed in this study enables suitable operating conditions for cross-type and double T-type form CZE systems to be established without the need for an experimental trial-and-error approach.
Keywords: Capillary Zone Electrophoresis (CZE), Absolute mobility, Ionic migration factor, Particle in cell (PIC) method. Non-aqueous solvents.