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Handbook of Size Exclusion Chromatography and Related ...

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Figure 6 Schematic representation <strong>of</strong> a (large) macromolecule adsorbed in a narrow<br />

adsorbent pore at high 1 value.<br />

further experimental material <strong>and</strong> also calculation <strong>of</strong> steric <strong>and</strong> conformational<br />

feasibility <strong>of</strong> the U-turn arrangement macromolecules (kinked<br />

conformation).<br />

The usual source <strong>of</strong> adsorption for electroneutral species are dipole–dipole<br />

<strong>and</strong> dipole-induced dipole interactions between analyte <strong>and</strong> column fillings.<br />

Therefore, important adsorption phenomena are observed mainly for polar<br />

macromolecules. The most common HPLC adsorbents are silica gels with active<br />

silanol groups. Adsorption on siloxane groups is expected to be much weaker.<br />

Unexpectedly large polar adsorptive activity was, however, also observed in<br />

poly(styrene-co-divinyl benzene) column packings (18,19) (see also Secs 4.1.1<br />

<strong>and</strong> 4.1.2). HPLC column fillings will be discussed in Sec. 4.1.<br />

As mentioned, analyte adsorption is strongly affected by the nature <strong>of</strong> the<br />

eluent (Secs 1<strong>and</strong> 4.2). Astrong solvent, which fully suppresses adsorption <strong>of</strong> a<br />

polymer on a given column packing at given temperature (<strong>and</strong> pressure) (1 0) is<br />

termed a desorli while a weak solvent, which promotes full adsorption <strong>of</strong> a<br />

polymer on a given column packing at given temperature (<strong>and</strong> pressure) is called<br />

an adsorli (1 1cr). Evidently, the adsorli for a polymer on a sorbent may turn out<br />

to be a desorli for another polymer on the same or another sorbent, or at another<br />

Figure 7 Schematic representation <strong>of</strong> adsorption <strong>of</strong> a large macromolecule (containing<br />

polar moieties) on silica gel C18 bonded phase containing free silanols.<br />

© 2004 by Marcel Dekker, Inc.

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