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Handbook of Size Exclusion Chromatography and Related ...

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Figure 8 Effect <strong>of</strong> particle size on polystyrene oligomer separation using PLgel 100 A ˚<br />

column, 300 7.5 mm; (a) 10 mm, (b) 5 mm, (c) 3 mm; eluant tetrahydr<strong>of</strong>uran, flow rate<br />

1mL/min, detector UV 254 nm.<br />

reduce h. In addition the porous frits at the inlet <strong>and</strong> outlet <strong>of</strong> SEC columns present<br />

a further potential source <strong>of</strong> shear as they are comprised <strong>of</strong> narrow channels that<br />

can also be considered as capillaries. The frit porosity should be selected in<br />

accordance with the particle size <strong>of</strong> the packing so as to contain the packing<br />

material while not inducing polymer shear degradation.<br />

Molecular shear phenomena are evidenced by peak splitting or lower than<br />

expected calculated molecular weight values (23). Experimental data (24) have<br />

shown that using 5 mm particle size, packings errors <strong>of</strong> 15–30% in molecular<br />

weight can be observed for narrow distribution polystyrene st<strong>and</strong>ards greater than<br />

4,000,000 g/mol. In these applications larger particle size (10–20 mm) columns<br />

are most suitable <strong>and</strong> compensation for their lower efficiency is made by the<br />

addition <strong>of</strong> more columns in series.<br />

4 AQUEOUS SEC<br />

4.1 Introduction<br />

The first polymeric packings were developed primarily for the analysis <strong>of</strong> natural<br />

polymers <strong>and</strong> they were based on lightly crosslinked polymer networks that<br />

produced s<strong>of</strong>t gel packings (8). These s<strong>of</strong>t gels, based on dextran or agarose,<br />

develop porosity between the polymer chains or between clusters <strong>of</strong> polymer<br />

© 2004 by Marcel Dekker, Inc.

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