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Handbook of Size Exclusion Chromatography and Related ...

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applications will be mentioned only for illustration <strong>and</strong> as aguide for the choice<br />

<strong>and</strong> evaluation <strong>of</strong> appropriate methods to solve aparticular analytical problem.<br />

2 STRATEGIES FOR TWO-DIMENSIONAL LIQUID<br />

CHROMATOGRAPHY OF COMPLEX POLYMERS<br />

Two-dimensional HPLC instruments comprise at least two different <strong>and</strong><br />

independent separation systems C#1 <strong>and</strong> C#2 (Fig. 3). The latter are represented<br />

eitherbydifferentcolumnfillingsordifferentmobilephases,orboth.Temperature<br />

variations are so far less common in 2D-HPLC <strong>of</strong> polymers. In some specific<br />

systems pressure changes may be utilized [for example, in supercritical fluid<br />

chromatography <strong>of</strong> complex polymer (6)].<br />

Two-dimensional chromatographic separations were pioneered in gas<br />

chromatography <strong>and</strong> in thin layer chromatography. Their development was<br />

motivated by an effort to increase resolution <strong>of</strong> analytical separations, that is, to<br />

raise the number <strong>of</strong> substances that could be resolved by the enhanced peak<br />

capacity <strong>of</strong> chromatographic systems. Grushka (7) has shown that the number <strong>of</strong><br />

peaks nthat can be separated in aone-dimensional isocratic chromatographic<br />

system, that is, its peak capacity,can be calculated from the following equation:<br />

n¼1þ N0:5<br />

4<br />

ln VR,n<br />

Vm<br />

Figure 3 Schematic representation <strong>of</strong> atwo-dimensional HPLC system for complex<br />

polymer separation. Pst<strong>and</strong>s for pumping systems, Cfor column systems, <strong>and</strong> Dfor<br />

detectors. Pumping system P#2 is needed if two different mobile phases or different flow<br />

rates <strong>of</strong> eluents are applied. Iisthe sample injector <strong>and</strong> RSR isthe sample reconcentration,<br />

storing, <strong>and</strong> reinjection, as well as eluent switching system. Wdenotes waste vent (for<br />

explanation see also Sec. 9).<br />

© 2004 by Marcel Dekker, Inc.<br />

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