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Handbook of Size Exclusion Chromatography and Related ...

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Figure 9 Silanol groups on silica surface.<br />

accessible to nucleophilic attack, <strong>and</strong> it requires cleavage <strong>of</strong> multiple bonds to<br />

cause loss <strong>of</strong> bonded phase. The performance <strong>of</strong> polymer bonded or encapsulated<br />

phases have been reported for a C18-silicone polymer bonded to high-purity silica<br />

(28), but this approach has not been extended to the development <strong>of</strong> silica-based<br />

SEC packing materials.<br />

2.8 Deactivation<br />

The use <strong>of</strong> mobile-phase additives to deactivate silanol groups is the most practical<br />

way to make them inaccessible to solute molecules. This approach is based on the<br />

well-known observation from adsorption chromatography that the activity <strong>of</strong> silica<br />

gel is strongly dependent on the presence <strong>and</strong> amount <strong>of</strong> water in a (largely)<br />

nonaqueous mobile phase. Thus, in adsorption chromatography, the retention <strong>of</strong><br />

© 2004 by Marcel Dekker, Inc.

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