Determination of electroosmotic flow in nonaqueous capillary electrophoresis

Mobility of the electroosmotic flow (mu(EOF)) 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 mu(EOF) were determined at a different ionic strength in basic conditions, and an absolute electroosmotic flow mobility (mu(EOF,0)) was extrapolated according to the Debye-Huckel Onsager model. The obtained mu(EOF,0) values were correlated with the solvent's relative permittivity (epsilon) and viscosity (eta). A good correlation (r2=0.867) between mu(EOF,0) and the solvent's epsilon/eta 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 mu(EOF,0) and epsilon/(eta x DN) was superior, with a r2 of 0.943 for 10 pure solvents.