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Preparation of a poly(styrene-co-divinylbenzene-co-methacrylic acid) monolithic stationary phase for the use in capillary electrochromatography (CEC) has been improved by optimizing the polymerization conditions. It is observed that the reaction time strongly affects column efficiency, while the proportion of isooctane in porogen influences peak symmetry of some solutes seriously. The lifetime of the monolithic columns prepared mainly depends on the pH of buffers used. Reproducibility of electroosmotic flow (EOF) from batch to batch columns are lower than 2.8% relative standard deviation. Unlike other types of capillary electrochromatographic monoliths, a pH-dependent EOF was observed on this type of column. Separation of various types of compounds including aromatic hydrocarbons, hormones, anilines, basic pharmaceuticals, and peptides was achieved. The facile preparation and wide application of this monolithic column may make styrene-based polymer a potential stationary phase in CEC.

A capillary electrochromatography (CEC) monolithic column with zwitterionic stationary phases was prepared by in situ polymerization of butyl methacrylate, ethylene dimethacrylate, methacrylic acid, and 2-(dimethyl amino) ethyl methacrylate in the presence of porogens. The stationary phases have zwitterionic functional groups, that is, both tertiary amine and acrylic acid groups, so the ionization of those groups on the zwitterionic stationary phase was affected by the pH values of the mobile phase, and further affects the strength and direction of the electroosmotic flow (EOF). Separations of alkylbenzenes and polycylic aromatic hydrocarbons based on the hydrophobic mechanism were obtained. Separation of various types of polar compounds, including phenols, anilines, and peptides, on the prepared column were performed under CEC mode with anodic and cathodic EOF, and different separation selectivities of those polar analytes were observed on the monolithic capillary column by using mobile phases with different pH values.Ionizable groups on the surface of the stationary phase are necessary to generate substantial electoosmotic flow (EOF) for capillary electrochromatography (CEC). 1 Strictly speaking, most stationary phases used in CEC are ion-exchangers. Silica-based packing materials, which have been most widely used in CEC and can be regarded as weak cation exchangers, generate cathodic EOF due to the ionization of the residual silanol groups on the surface of packings. Recently, strong ion exchangers and so-called mixed-mode packing materials consisting of ionic groups such as sulfonic acids or quaternary amines and hydrocarbon chains have attracted much attention in CEC, because these packings ensure stable EOF over an extended pH range. 2 The direction of the EOF depends on the charges on the surface of the stationary phases, so stationary phases with positively charged functional groups, such as amino groups or ammonium groups, generate an EOF from cathode to anode, whereas stationary phases carrying negatively charged groups, such as sulfonic acid and carboxylic acid, generate cathodic EOF. To date, the vast majority of reports on CEC concern EOF with one direction, that is, cathodic or anodic EOF, for a CEC column; however, zwitterionic stationary phases, which can make it possible to generate EOF with different directions for one column, are seldom investigated in CEC. In fact, there are many reports concerning chromatographic separation with zwitterionically modified materials, although it is still one of the new liquid chromatography separation modes studied in recent years. [3][4][5][6] Hu et al. 7 established the zwitterionic functionality via dynamically adsorbing the ODS (octadecyl silica) column with a sulfobetaine-type zwitterionic surfactant by the interaction between the C 18 groups on the surface and the hydrophobic tail of the surfactant. To overcome the drawback of inferior stability due to loss of functional moieties from the dynamically attached layer on the surface of stationary phases, ...