Nonaqueous capillary electrophoresis in microchip: Influence of solvent properties on separation performance

The aim of this study was to simplify the solvent selection for non-aqueous microchip CE by investigating the effect of different organic solvents on the separation speed and resolution of two simple and stable fluorescent dyes. Organic solvents, including methanol (MeOH), acetonitrile (ACN), dimethylsulfoxide (DMSO), formamide (FA) and N,N-dimethylformamide (DMF) were evaluated against water. The electrophoresis behaviors of Rhodamine123 and Fluorescein sodium under different electric field strength were studied systematically in a simple cross microchip. Two models for predicting the resolution and separation speed based on solvent property such as viscosity (η), dielectric constant (ε), and zeta potentials (ς), were generated and tested. The experimental results were in agreement with the theoretical prediction when low separation voltages were applied in most solvents except FA. Solvents with a high ε ς/η will tend to speed up the separation, and solvents with a low ε ς will tend to increase the resolution of the analytes.