Evaluation of 2,3-epoxypropyl groups and functionalization yield in glycidyl methacrylate monoliths using gas...

Poly(glycidyl methacrylate-co-ethylene dimethacrylate) (poly(GMA-co-EDMA)) is most frequently used as parent monolith to obtain stationary phases with a variety of surface chemistries for liquid chromatography and capillary electrochromatography. Functionalization is performed by opening the accessible 2,3-epoxypropyl groups of the monolith with a suitable reagent. The number of 2,3-epoxypropyl groups which are accessible before and after the functionalization reaction, and the grafting yield, are important parameters, required both to optimize functionalization and to interpret the chromatographic performance of functionalized monoliths. In this work, a method capable of providing this information for parent and functionalized poly(GMA-co-EDMA) monoliths prepared both in silica capillaries and in other supports is proposed. First, sulfuric acid and lithium aluminium hydride (LiAlH4) are sequentially used to release the 2,3-epoxypropyl groups as glycerol, which is subsequently determined by GC. About 6.0mmol of 2,3-epoxypropyl groups per gram of monolith was found in this work for the parent monoliths prepared in silica capillaries using UV-initiation. The monoliths were also functionalized using ammonia (NH3), diethylamine (DEA) and epinephrine, and the amount of residual 2,3-epoxypropyl groups, and hence the functionalization yield, were established by also measuring the GC peak of glycerol. The amounts of 2,3-epoxypropyl groups and the derivatization yields were established with RSDs of 1.7 and 3.4%, respectively. The proposed method was also applied to the characterization of poly(GMA-co-EDMA) monoliths prepared in glass vials. Significant differences with respect to those prepared in 100μm I.D. silica capillaries were evidenced.