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Handbook of Size Exclusion Chromatography and Related ...

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Figure 8 Schematic representation <strong>of</strong> a macromolecule partitioned between bonded C 18<br />

groups <strong>and</strong> mobile phase.<br />

adjustments <strong>of</strong> enthalpic partition usually require relatively larger changes in<br />

eluentcompositionorintemperature.Fullretention<strong>of</strong>macromoleculeswithinthe<br />

columnmaybemoredifficultthaninthecase<strong>of</strong>adsorption(28)unlessaverypoor<br />

solvent is used as mobile phase.<br />

Itisanticipatedthatenthalpicpartition <strong>of</strong>macromolecules,especiallyinthe<br />

narrow pore column packings <strong>and</strong> when approaching polymer phase separation<br />

limits, may lead to b<strong>and</strong> broadening <strong>and</strong> splitting phenomena. Retentionvolumes<br />

<strong>of</strong>polymerssubjecttoenthalpicpartitiondependontemperature<strong>and</strong>possiblyalso<br />

on pressure.<br />

The schematics <strong>of</strong> asituation depicting the hybrid enthalpic partition/<br />

adsorption retention mechanism <strong>of</strong> macromolecules is shown in Fig. 9.<br />

3.2.3 Phase Separation: Solubility<br />

As shown in Sec. 3.2.2, the thermodynamic quality <strong>of</strong> the mobile phase toward<br />

eluted polymers strongly affects enthalpic partition <strong>of</strong> macromolecules. Moreover,<br />

quality <strong>of</strong> eluent also somewhat influences exclusion behavior <strong>of</strong> macromolecules<br />

Figure 9 Schematic representation <strong>of</strong> macromolecules simultaneously adsorbed on free<br />

silanols <strong>of</strong> silica gel <strong>and</strong> partitioned between bonded C18 groups <strong>and</strong> mobile phase.<br />

© 2004 by Marcel Dekker, Inc.

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