Determination of electroosmotic flow in nonaqueous capillary electrophoresis

Mobility of the electroosmotic flow (μEOF) in fused-silica capillaries strongly depends on the nature of the background electrolyte. In this study, 27 solvent systems were investigated, namely water, methanol, ethanol, 2-propanol, 1-butanol, acetonitrile (MeCN), formamide, N-methylformamide (NMF), N,N-dimethylformamide and dimethyl sulfoxyde, as well as 8 hydroorganic and 9 organic mixtures. For each system, six μEOF were determined at a different ionic strength in basic conditions, and an absolute electroosmotic flow mobility (μEOF,0) was extrapolated according to the Debye–Huckel Onsager model. The obtained μEOF,0 values were correlated with the solventʹs relative permittivity (ɛ) and viscosity (η). A good correlation (r2 = 0.867) between μEOF,0 and the solventʹs ɛ/η ratio was demonstrated, except for two solvents (MeCN and NMF). Furthermore, the donor number (DN) of a solvent took into account the possible zeta potential modification in the electric double layer near the capillary wall. Consequently, the relationship between μEOF,0 and ɛ/(η × DN) was superior, with a r2 of 0.943 for 10 pure solvents.