Electrochromatographic properties of synthetic poly(styrene-divinylbenzene) encapsulated packing material and sulphonic cation-exchange phase based on the former.

Objective: To develop new kinds of stationary phases suitable for applications in capillary electrochromatography (CEC), as well as in LC, which can be tailored to realize selective separations of solutes difficult to separate with conventional stationary phases.

Methods: Purchased spherical silica particles (5 microm) were refluxed in anhydrous toluene with vinyl-triethoxysilane for 18 h, to modify the surface with vinylsilyl groups. The silylated silica particles were subsequently stirred in an n-henanol-acetonitril mixture (1:4, volume fraction) for 18 h. Styrene and divinylbenzene in the mixture co-polymerized to form a crosslinked encapsulation layer on the silica surface, and bonded on the surface vinyl groups at the same time, both reactions were initiated by azo-iso-butyronitrile. The poly(Styrene-divinylbenzene) encapsulated silica(PS-DES) produced can be used as a non-conventional stationary phase for CEC itself. By sulphonation of the PS-DES phase with chlorosulphonic acid, strong cation-exchange stationary phase of sulphonic type was obtained.

Results: The manufactured PS-DES as well as the sulphonated phases were respectively packed into capillaries,and the columns thus prepared were tested for their chromatographic characteristics. It was found that the PS-DES phase showed reversed-phase characteristics. Due to the phenyl groups in the encapsulated polymer, it introduced pi-pi electronic interaction between the solutes molecules and stationary phase during the chromatographic separation process, therefore it showed unique selectivity on separating aromatic compounds, also polar- as well as some alkaline drugs was analyzed on the column packed with the phase. It was demonstrated that the sulphonated phase could be used to prepare columns for the separation of alkaline drugs, symmetric peaks were obtained for them and base-line separation was realized.

Conclusion: It is possible that these stationary phases prepared can be used for solving the analytical problems in which non-conventional selectivity are needed ( the analyses of alkaline drugs are examples) In some cases, the analysts can realize the anticipated separation results based on the different separation mechanism from that of the conventional stationary phases.