Irregular Silica

Analytical hplc these days is nearly always done with microparticulate column packings, which are small porous particles, usually spherical or irregular silica, with nominal diameters of 3,5 or 10 fxm. They combine the best features of the other two types, having high efficiency as well as a large surface area. In bulk, the appearance of a microparticulate silica resembles that of a fine talcum powder. With microparticulates, dry packing methods result in column beds that are unstable under pressure, so they are packed into columns using a slurry of the material in a suitable solvent and under considerable pressure. 

Column packed with Cyclobond I, /3-cyclodextrin bonded to irregular silica gel. 

The increase in scale of preparative HPLC, brought about predominantly by the invention of DAC, resulted in a proportionate demand for high quality stationary phases. A move from the rather crude irregular silica based media used for normal... 

I have known the performance of irregular silica particles to improve with time and it has been postulated that this is due to erosion of the media to such an extent that the stationary phase has eventually become spherical. 

Figure 7.9 Irregular and spherical HPLC material (scanning electron micrographs, taken in the Electron Microscopy Laboratory ofthe Inorganic Chemistry Institute, University of Berne). Magnification x700 (left) and x7000 (right). Above irregular silica, mean particle diameter Spm (Baker silica). Below spherical silica gel, mean particle diameter 5 mm (Spherisorb ODS, i.e. chemically modified silica).

CH2),7CH3, endcapped, monofunctional, 55-105 pm, 125-A pores, irregular silica... 

A pores, irregular silica Other Bonded Phases... 

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