Silica Particles Supported Zwitterionic Polymer Monolith For Solid Phase Extraction And Microcolumn Liquid Chromatography

A silica particles supported zwitterionic polymeric monolithic column, shortened as the supported column(S-column), was prepared by in-situ polymerization of methacrylic acid, ethylene dimethacrylate and 2-(dimethyl amino) ethyl methacrylate in the presence of a ternary porogenic solvent containing water, methanol and cyclohexanol in a 250 ?m i.d. fused silica capillary pre-packed with 5 ?m bare silica particles. In the S-column, a thin layer of the polymers were formed around the silica particles in the form of nano-globules, leaving the interstitial spaces between the particles free for liquid flow. The effects of preparation conditions on the morphology of the monolith were investigated by SEM images and backpressure measurements. The selected volumetric ratio of porogens, monomer concentration, polymerization time and temperature are 1:1:8(water/methanol/cyclohexanol), 25%(v/v), 5 h and 60?, respectively.The S-column was evaluated by comparison with its conventional organic counterpart in terms of morphology, mechanical stability, permeability, swelling-shrinking behavior, capacity and efficiency. The results demonstrate that the S-column is superior to its counterpart in all the terms with the exception of permeability. The above merits and zwitterionic property of the S-column were further confirmed by separate separations of 4 inorganic anions and 3 organic cations.Finally, the S-column was used as a solid phase extraction column for the analysis of sodium benzoate in carbonated beverage. Several parameters including sample p H value, sample flow rate, eluent p H value, eluent flow rate and contents of Na2HPO4 and methanol in the eluent were investigated and the best extraction conditions are 2, 0.8 ?L/min, 7, 1.2 ?L/min, 0.05 mol/L and 50%, respectively. The S-column was applied to enrich the sodium benzoate in a standard solution, and the enrichment factor of the solid phase extraction is 272, and the limit of detection is 0.052 ?g/m L(S/N=3). The solid phase extraction(SPE) column coupled with a ODS particles packed capillary column was applied to extraction and separation of the sodium benzoate in commercial sodas. The relative standard deviations were 18% and 25% for peak height and retention time(RSD%, n=5), respectively.