Directed control of electroosmotic flow in nonaqueous electrolytes using poly(ethylene glycol) coated capillaries

Poly(ethylene glycol) (PEG)-coated capillaries exhibit unique properties in nonaqueous electrolytes. Immobilized PEG interacts significantly with diff erent cations present in nonaqueous electrolytes. This can induce a positiv e surface charge on PEG-coated capillaries and results in an adjustable ano dic electroosmotic flow (EOF) in nonaqueous electrolytes whereas a reduced cathodic EOF is observed in aqueous electrolytes. The EOF can reversibly be adjusted by the variation of the electrolyte constitution, namely the type of the solvent used and the nature and concentration of background cations . In methanol and especially in acetonitrile electrolytes the magnitude and also the direction of EOF is strongly dependent on the water content. Usin g different alkali metal cations, the EOF can be increased, reduced, or eve n reversed depending on the nature of the cation. The directed manipulation of EOF in methanolic electrolytes using PEG-coated capillaries was applied for optimization of nonaqueous capillary electrophoretic separations of ac idic compounds with regard to reproducibility, resolution, and analysis tim e.