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Handbook of Size Exclusion Chromatography and Related ...

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Figure 14 Schematic representation <strong>of</strong> eluent gradient HPLC <strong>of</strong> two polymers A<strong>and</strong> B<br />

with different chemical structures or physical architectures. The linear eluent gradient is<br />

used with isocratic periods in the starting <strong>and</strong> final stage. Arrows denote the eluent<br />

composition, which acts as a barrier for progression <strong>of</strong> macromolecules with a particular<br />

composition. Solvent S 1 promotes sample elution, S 2 promotes sample retention. Sample B<br />

exhibits larger enthalpic interaction with the column filling than sample A.<br />

limiting conditions <strong>of</strong> desorption (74). Macromolecules that are retained near the<br />

column inlet start eluting at different eluent compositions in dependence on their<br />

molar mass, chemical structure, <strong>and</strong> architecture. During their passage along the<br />

column, polymer species are, however, stacked on the eluent barrier only<br />

according to their chemical structure <strong>and</strong>/or architecture while the molar mass<br />

effect may be suppressed, similarly as in, for example, liquid chromatography<br />

under limiting conditions <strong>of</strong> desorption (Fig. 12) (73). In adsorption <strong>and</strong> partition<br />

EG HPLC, the eluent composition that just decelerates macromolecules nearly<br />

corresponds with critical conditions (75,76).<br />

Thishypothesisexplainsseveralfeatures<strong>of</strong>polymerEGHPLC.Thecolumn<br />

is used mainly for sorting <strong>of</strong> macromolecules by selective hampering <strong>of</strong> their fast<br />

progression.Macromoleculeswithdifferentmolarmassesbutsimilarcomposition<br />

<strong>and</strong>/or architecture are stacked within the same loci <strong>of</strong> eluent composition.<br />

Therefore, EG HPLC columns have much higher loadability than, for example,<br />

SEC columns. Further, EG HPLC columns can be short, just to allow larger<br />

macromolecules that are stronger interacting species, which started moving later,<br />

tocatchsmallerspecieswithsimilarchemicalstructure<strong>and</strong>architecture.Zones<strong>of</strong><br />

species with similar chemical structure or architecture are narrow due to focusing<br />

effects (77,78), which is similar to HPLC <strong>of</strong> macromolecules under limiting<br />

conditions (Figs 11 <strong>and</strong> 12). With well chosen column packing <strong>and</strong> nature <strong>of</strong><br />

© 2004 by Marcel Dekker, Inc.

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