Allyl-silica hybrid monoliths and electroconductive polymer (polypyrrole) as new stationary phases for chromatography
Two materials were explored as potential stationary phases for chromatography: allyl monolithic organo silica and polypyrrole (PPY). Allyl-functionalized silica hybrid (I) monolithic structures were synthesized in a "one-pot" reaction approach for use in liquid chromatography. The monolithic material provided a silica support material containing accessible allyl organic groups. The allyl moiety at the surface was modified by means of hydrosilylation reactions using n-octyldimethylsilane (C 8 -DMS) or benzyldimethylsilane (benzyl-DMS), imparting different surface characteristics, hence different chromatographic selectivity. The generated stationary phase is anchored to the silica surface by a Si-C bond which is more pH stable than the traditional stationary phase. The hydrosilylation reaction conditions were studied in an effort to maximize the amount of functional group reacting with the allyl group on the surface of the material. The conversion by the hydrosilylation reaction was 30%, providing a surface coverage of 2.1 μmol · m -2 for the C 8 group and 2.0 μmol · m -2 for the benzyl group. Capillary liquid chromatography (CLC) and capillary electrochromatography (CEC) were used to demonstrate the potential chromatographic applicability of the hybrid monolith. The pH stability of the allyl-silica hybrid monolithic column proved to be superior to that of a conventionally prepared monolithic column. Specific details of the preparation, characterization, and the initial chromatographic performance of the allyl-silica hybrid monolith and its C 8 - or benzyl-hydrosilylated derivatives are reported. Most silica monolithic columns for capillary liquid chromatography are prepared in capillaries with less than 100 μm internal diameter to avoid one of the most prominent problems related to the synthesis of silica monolithic columns: volume shrinkage. One type of the allyl-functionalized silica hybrid monolithic structures reported here was studied in an attempt to reduce the volume shrinkage during the aging and drying processing related to the synthesis of the material. A third co-precursor was incorporated into the original reaction composition containing tetramethoxysilane (TMOS) and allyltrimethoxysilane (allyl-TrMOS). The volume shrinkage was reduced significantly by incorporating the third co-precursor (e.g. dimethylmethoxysilane DMDMOS). Other important parameters that influence the volume shrinkage and monolithic structures, such as the concentration of acid catalyst, the amount and type of silanes, the concentration of water, the amount of porogenic agent, and the amount of urea, were also studied. Good peak asymmetry was obtained for the separation of anilines in the 100 μm allyl-silica hybrid monolithic column fabricated with three silane precursors. Polypyrrole (PPY) was investigated as a potential stationary phase for thin layer chromatography (TLC) in an effort to take advantage of its characteristics by electrical potential switching. Thin layers of PPY were deposited onto a porous layer of glass previously coated on glass plates. Changes in conductivity of the PPY coating were studied by applying positive and negative potentials. The redox reversibility of PPY on the glass plates was compared with that of PPY on platinum plates by cyclic voltammetry (CV). The results indicate that under our experimental conditions, the property changes of PPY are only partially reversible under the potential switching conditions. The degradation of PPY electroactivity is much quicker on the glass plates than on the platinum plates.