Determination of electroosmotic flow in nonaqueous capillary electrophoresis

Abstract

Mobility of the electroosmotic flow ( μ 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 μ EOF were determined at a different ionic strength in basic conditions, and an absolute electroosmotic flow mobility ( μ EOF,0) was extrapolated according to the Debye–Huckel Onsager model. The obtained μ EOF,0 values were correlated with the solvent's relative permittivity ( ɛ) and viscosity ( η). A good correlation ( r 2 = 0.867) between μ EOF,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 μ EOF,0 and ɛ/( η × DN) was superior, with a r 2 of 0.943 for 10 pure solvents.