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Handbook of Size Exclusion Chromatography and Related ...

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2. Identify sample solvents. First apply single <strong>and</strong>, if necessary also<br />

mixed liquids <strong>of</strong> various polarities. Good advice on polymer solubility<br />

can be found in the Polymer <strong>H<strong>and</strong>book</strong> (52). Once the sample is<br />

dissolved, several bulk methods <strong>of</strong> polymer analysis <strong>and</strong> characterization<br />

in solution can be applied from conventional spectrometry <strong>and</strong><br />

NMR up to SEC. The latter method may also reveal the presence <strong>of</strong><br />

species with large differences in their molar masses (molecular sizes)<br />

in the sample. If so, preparative SEC separation can produce fractions<br />

for further identification procedures. In any case, SEC also gives<br />

valuable first estimate(s) on molar mass(es) <strong>of</strong> the sample<br />

(components).<br />

3. Full retention–elution (FRE) (Sec. 7) with nonporous bare silica <strong>and</strong><br />

later with nonporous silica C18 packing can help to separate the<br />

sample into chemically different components, which are further<br />

characterized with on-line SEC (Fig. 16). Apply bare silica FRE<br />

column packing for the sample (constituents) carrying polar groups.<br />

Adsorption will be the leading retention mechanism (Sec. 3.2.1).<br />

Nonpolar sample constituents will be more easily mutually separated<br />

with silica C 18FRE column packing, in which macromolecules will<br />

be retained mainly by enthalpic partition (Sec. 3.2.2). For nonpolar<br />

sample constituents, aphase separation retention mechanism can also<br />

be applied (Sec. 3.2.3), preferably with bare silica FRE column<br />

packing. For full adsorption–desorption (FAD) columns packed with<br />

bare silica use the least polar solvent available for sample adsorption<br />

<strong>and</strong> polar solvent(s) for sample desorption. The experimental<br />

approach wih silica C 18 FRE column is reversed. Evidently, the<br />

initial eluent must be an efficient nonsolvent for the sample if the<br />

FRE retention mechanism is based on the phase separation retention<br />

mechanism.<br />

4. Fractions from repeated or preparative FRE separations can be further<br />

analyzed by spectrometry including NMR <strong>and</strong> MS. The FRE fractions <strong>of</strong><br />

the sample can also be injected into an eluent gradient HPLC system for<br />

further, more selective discrimination. An EG HPLC system is to be<br />

chosen on the base <strong>of</strong> sample behavior in the FAD column. This means<br />

that polar sample constituents are separated by applying a polar column<br />

packing (for example, bonded amino-phase) <strong>and</strong> eluent gradient with<br />

increasing concentration <strong>of</strong> polar solvent.<br />

5. If necessary, fractions from the EG HPLC system can be forwarded into<br />

the SEC column for the final molecular characterization (quasi threedimensional<br />

HPLC).<br />

Good luck!<br />

© 2004 by Marcel Dekker, Inc.

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