Open‐tubular capillary electrochromatography of small polar molecules using etched, chemically modified capillaries

The migration characteristics of small polar molecules are evaluated on etched, chemically modified capillaries with four different moieties (C5, C18, diol and cholesterol) bonded onto a silica hydride surface. The effects of pH on migration are used to determine the possible contributions of eletrophoretic mobility, electroosmotic flow (EOF) and analyte/bonded phase interactions. The EOF on etched capillaries is more complicated than on ordinary fused capillaries because it changes from anodic to cathodic as the pH is raised. A mixture of neurotransmitters and related compounds is used to further evaluate the effects of the bonded moiety on the separation properties of this particular electrophoretic format.