Polystyrene bound stationary phase of excellent separation efficiency based on partially sub-2µm silica monolith particles.

Partially sub-2µm porous silica monolith particles have been synthesized by a renovated procedure and modified to polystyrene coated silica particles with excellent separation efficiency when used as chromatographic media. In the procedure of preparing silica monolith particles in this study, subtle control of formulation of the reaction mixture and multi-step heating followed by calcination, without any washing and sieving process, enabled formation of silica particles characterized by proper particle and pore size distribution for high separation efficiency. 3-Chloropropyl trimethoxysilane was used as the halogen terminal spacer to combine the initiator to silica particles. Uniform and thin coating of polystyrene layer on initiator attached silica particles was formed via reversible addition-fragmentation chain transfer (RAFT) polymerization. Micro-columns (1.0mm ID and 300mm length) were packed with the resultant phase and their chromatographic performance was elucidated by HPLC. A mobile phase of 60/40 (v/v) acetonitrile/water containing 0.1% TFA and a flow rate of 15µL/min were found to be the optimized conditions leading to number of theoretical plates close to 50,000 (165,000m(-1)). This is the very first study to get such highly efficient HPLC columns using a silica monolith particulate stationary phase.

Preparation and characterization of alkyl methacrylate-based monolithic columns for capillary gas chromatography applications.

Gas chromatography (GC) is considered the least common application of both polymer and silica-based monolithic columns. This study describes the fabrication of alkyl methacrylate monolithic materials for use as stationary phases in capillary gas chromatography. Following the deactivation of the capillary surface with 3-(trimethoxysilyl)propyl methacrylate (TMSM), the monoliths were formed by the co-polymerization of either hexyl methacrylate (HMA) or lauryl methacrylate (LMA) with different percentage of ethylene glycol dimethacrylate (EDMA) in presence of an initiator (azobisisobutyronitrile, AIBN) and a mixture of porogens include 1-propanol, 1,4-butanediol and water. The monoliths were prepared in 500mm length capillaries possessing inner diameters of 250µm. The efficiencies of the monolithic columns for low molecular weight compounds significantly improved as the percentage of crosslinker was increased, because of the greater proportion of pores less than 50nm. The columns containing lower percentages of crosslinker were able to rapidly separate a series of 8 alkane members in 0.7min, but the separation was less efficient for the light alkanes. Columns prepared with the lauryl methacrylate monomer yielded a different morphology for the monolith-interconnected channels. The channels were more branched, which increased the separation time, and unlike the other columns, allowed for temperature programming.