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surface. Each oligomeric chain consists of series of organic moieties, joined by silicon atoms to a
silanol group on the surface. After the last oligomer has been added, the end of the oligomer is capped
with trimethylchlorosilane or hexamethyldisilazane. The oligomeric phases are difficult to manufacture
as their synthesis involves a series of steps that are best carried out in a fluidized bed reactor. As a
consequence they are not, at present, commercially available. They do offer greater stability to aqueous
solvents and higher salt solutions than do the other bonded phases [16] and could, therefore, find
application in the separation of materials of biological origin. The third type of bonded phase, the 'bulk'
type phase, results from the use of a trifunctional silane reagent in the bonded phase synthesis.

An Oligomeric Bonded Phase
The bulk phase is polymeric in form, and is produced, for example, by the use of trichlorosilyl reagents
with water added to the silica, prior to reaction. If the silica surface is saturated with water, the
octyltrichlorosilane reacts with both the hydroxyls of the silica surface and the adsorbed water, causing
cross-linking and an octylsilyl polymer is built up on the surface. Due to the polymerization process, the
stationary phase has a multi-layer character and consequently, has been given the term 'bulk' phase. The
bulk phase can also be synthesized by alternately treating