Evaluation of micron sized silica based packing material for ultra high pressure capillary liquid chromatography.

摘要

According to chromatographic theory, columns packed with smaller particles should give better performance than those packed with larger particles. Previous research has shown that columns packed with 1 mum porous bridged ethyl hybrid (BEH) particles do not perform as well as theory would suggest they should. Dispersity in the size distribution of the particles was suspected as a cause for poor performance. Increasing amounts of 2 mum porous BEH particles were added to a batch of 1 mum BEH particles to investigate the importance of particle size and particle size distribution. These particle batches were evaluated on the basis of chromatographic analysis, packing density and flow resistance. Size distribution did not appear to explain the poor performance of the 1 mum particles.;The process for packing porous silica particles involves packing a slurry of particles using a slurry solvent at high pressure. The interaction between the slurry solvent and porous packing material is a very important element in producing well packed columns. If the particles do not suspend well in the slurry solvent, they can form aggregates. To determine the most suitable slurry solvent, ten different solvents were used to pack 1.0 mum porous BEH particles into capillary columns. The packing density and column efficiency were evaluated. Three slurry solvents were found to give noticeably better column performance than the others.;In order to increase packing density and reduce voids in packing, columns were placed in an ultrasonic bath either during or after the packing process. The ultrasonic energy allowed for particles to be compacted into a denser particle bed. Chromatographic evaluation of the columns after ultrasonication in some cases showed improvement in column efficiency due to increased packing density.;The relative importance of the resistance to mass transfer in the mobile phase, stagnant mobile phase and stationary phase were investigated for columns packed with 1 mum particles. This was determined by the unique dependence of each of these terms on retention factor (k') and it was concluded that the resistance to mass transfer in the mobile phase was the dominant contribution.