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Figure 20 Set <strong>of</strong> full retention–elution (FRE) columns, a real RSR system (sample<br />

storing <strong>and</strong> reconcentration device that also allows eluent switching). Combination <strong>of</strong><br />

the corresponding fractions is feasible. Column C#1 works continuously. V#1 <strong>and</strong> V#2 are<br />

n þ 1 port n-way switching valves, which are operated simultaneously. R#1 <strong>and</strong> R#2 are<br />

hydrodynamic resistors. D is a detector. C#1 <strong>and</strong> C#2 do not operate simultaneously in this<br />

simpler arrangement. For further explanations see the text.<br />

fractions combinedwithincorrespondingFREcolumn(s).Theentire arrangement<br />

can easily be automated for unattended operation.<br />

The conditions for the FRE retention mechanism choice were discussed<br />

in Sec. 7.<br />

10 DETECTION AND DATA REPRESENTATION IN 2D-HPLC<br />

OF COMPLEX POLYMER SYSTEMS<br />

Detectors <strong>and</strong> detection procedures are discussed in several chapters <strong>of</strong> this book.<br />

It is shown that detection in polymer HPLC made much progress in the 1990s.<br />

However, detectors remain one <strong>of</strong> the weak points <strong>of</strong> coupled <strong>and</strong> two-dimensional<br />

HPLC procedures <strong>of</strong> complex polymers.<br />

Concentration/mass detectors should selectively detect each constituent <strong>of</strong><br />

the complex polymer, for example, each type <strong>of</strong> monomer in the copolymers.<br />

There are, however, only a few complex polymer constituents that can be detected<br />

both universally <strong>and</strong> selectively by conventional detectors. For example, the total<br />

concentration <strong>of</strong> copolymers <strong>of</strong> styrene <strong>and</strong> methyl methacrylate can be monitored<br />

by means <strong>of</strong> UV photometers at about 235nm <strong>and</strong> polystyrene concentration can<br />

be measured selectively at a wavelength <strong>of</strong> 254–260nm (100). In any case, the<br />

photometric detectors, including UV-VIS diode array detectors, as well as infrared<br />

<strong>and</strong> fluorescence detectors, find important applications in 2D-HPLC <strong>of</strong> many<br />

complex polymer systems. Serious drawbacks <strong>of</strong> infrared spectroscopic detection<br />

lie in its relatively low sensitivity, as well as in the poor IR transparency <strong>of</strong> most<br />

mobile phases. Important progress was achieved by introduction <strong>of</strong> interfaces that<br />

© 2004 by Marcel Dekker, Inc.

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