Page 41 - Tandem Techniques

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employed for solute identification. The uncertainty of solute identification from (k') data, and other
measurements based on solute retention, is another reason why the use of tandem techniques is so
important and becoming so popular.

When silica gel is treated with an appropriate silane reagent, organic groups can be bonded to the
surface. Depending on the nature of the bonded moiety, the character of the surface can range from
strongly polar to dispersive or even ionic. The silanizing process will not be discussed in detail, but it
should be said that there are basically three types of reverse phase. The use of a silane with a single
functional group, such as octyldimethyl-chlorosilane, will react only with the hydroxyl groups on the
surface and produce the 'brush' type reverse phase. Many chromatographers consider that the two
methyl groups on the silicon atom of the reagent stearically hinders any further reaction with a directly
adjacent hydroxyl group. In fact, many consider that all attached organic groups are separated from
their neighbors by a silicon atom with a hydroxyl group attached (as depicted below). Nevertheless,
experimental proof of this remains forthcoming. stationary phases: brush type

A 'Brush' Type Bonded Phase

If the silica is treated alternately, with a bifunctional silane such as octyldichloro-silane and then water,
an oligomeric phase is built up on the