Box 25-1 Monolithic Silica Columns

Time is money. In commercial laboratories, the faster an analysis can be done, the less it costs. Monolithic silica columns enable us to increase the flow rate in liquid chromatography while retaining good separation.7 

Each column in the left-hand photograph is a single, porous silica rod polymerized from liquid precursors. The adjacent micrographs show the silica skeleton with a network of 2-pm pores. The inside of the skeleton contains a finer network of 13-nm pores that are too small to be seen in the micrographs. Approximately 80% of the volume of the rod is empty space. The 

Because of its open, rigid structure, solvent flows through the monolithic column with relatively little resistance. The same pressure required to obtain a flow rate of 1 ml./min with 3.5-pm spherical particles provides a flow rate of 9 mL/min in the monolithic column. At 9 mL/min, the plate height in the monolithic column is only 50% greater than the minimum plate height observed at 2 mL/min. 

Enlarged view. Invisible 13-nm pores are located within the silica skeleton. 

Adsorption chromatography on bare silica is an example of normal-phase chromatography, in which we use a polar stationary phase and a less polar solvent. A more polar solvent has a higher eluent strength. Reversed-phase chromatography is the more common 

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