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Handbook of Size Exclusion Chromatography and Related ...

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Mobile phase barriers can be <strong>of</strong><br />

. Isocratic or<br />

. Stepwise/continuous gradient type.<br />

Schematic representations <strong>of</strong> particular barrier approaches are shown in<br />

Figs. 11–13. Figure 11 shows the action <strong>of</strong> an isocratic barrier <strong>of</strong> mobile phase.<br />

Eluent with constant composition promotes full retention <strong>of</strong> polymer analytes B<br />

<strong>and</strong> C due to their adsorption or enthalpic partition or phase separation<br />

(precipitation) within the column, while analyte A is not retained by the eluent<br />

barrier. Sample containing polymers A, B, <strong>and</strong> C is dissolved <strong>and</strong> injected in a<br />

liquid that prevents their adsorption, partition, or precipitation (desorli/displacer<br />

or good solvent). Macromolecules tend to travel faster than the zone <strong>of</strong> their<br />

initial solvent. However, polymer B cannot leave the zone <strong>of</strong> its original solvent<br />

<strong>and</strong> elute corresponding to the exclusion retention mechanism because the<br />

eluent barrier hinders its fast progression. Nonretained polymer A will freely<br />

leave the initial solvent zone <strong>and</strong> elute in the SEC mode separately from<br />

retained species B <strong>and</strong> C. Molar mass <strong>and</strong> molar mass distribution <strong>of</strong> polymer<br />

A can be determined in the conventional way. Retention properties <strong>of</strong> eluent<br />

<strong>and</strong> displacement properties <strong>of</strong> sample solvent can be optimized so that polymer<br />

species <strong>of</strong> identical or similar chemical structure or architecture (polymer B)<br />

will travel with the same velocity near the front <strong>of</strong> the initial sample solvent<br />

zone <strong>and</strong> elute from the HPLC column independently <strong>of</strong> their molar mass<br />

(5,6,73). A sample which exhibits still higher affinity toward the column filling<br />

Figure 11 Schematic representation <strong>of</strong> liquid chromatography under limiting conditions<br />

<strong>of</strong> adsorption. A, B, <strong>and</strong> C are polymers injected, S is the elution (desorption) promoting<br />

sample solvent. Eluent promotes adsorption <strong>of</strong> polymers B <strong>and</strong> C. For detailed explanation<br />

see the text.<br />

© 2004 by Marcel Dekker, Inc.

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