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 solvent's relative permittivity (ɛ) and viscosity (η). A good correlation (r2 = 0.867) between μEOF,0 and the solvent's 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.