Silica factors affecting surface properties

It is most often prepared by acid hydrolysis of sodium silicate followed by emulsification in an alcohol water mixture and subsequent condensation to give solid silica gel. This is then washed and dried for use as HPLC column packing. The exact conditions under which these procedures are carried out (e.g. pH, catalysts, temperature) will affect the properties of the resulting material. The most important qualities with regard to the chromatographic performance of the gel are the average particle size, the particle shape, the specific surface area and the pore size. Other factors which are also important are the pH of the gel surface, the number of active silanol groups and the presence of metal ions. 

In summary, whilst the toxicity of silica nanomaterials is generally low-and even more so at lower concentrations-a variety of factors which include the nanomaterials size, shape, surface properties, dopants, treatment dose and time, all affect their toxicity to similar degrees. Although such toxicity is a relatively recently investigated topic, and many studies are still at the experimental stages, the above-described factors are crucial for the safe use of silica nanomaterials in a variety of biological applications. 

The support will affect the retention to an extent that depends on the properties of its surface and the components in the ion-pair [3, 43]. When silica based material is used as support, the deviations between the obtained capacity factors and those predicted from batch extraction data are usually significant [44, 45]. Careful thermostatting of the whole chromatographic system is a prerequisite for stable retention. 

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