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Handbook of Size Exclusion Chromatography and Related ...

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distributions <strong>of</strong> complex polymers are very important for both science <strong>and</strong><br />

technology,provided they are evaluated critically.These data may allow abetter<br />

underst<strong>and</strong>ing <strong>of</strong> many polyreactions, optimization <strong>of</strong> polymer production<br />

processes,<strong>and</strong> tracing sources <strong>of</strong>problems inmanufacturing <strong>of</strong>complex polymers.<br />

The data from 2D-HPLC <strong>of</strong> complex macromolecules are usually<br />

represented by contour plots (see Fig. 2) or contour maps in which detector<br />

response, sample composition, or relative concentration are represented against<br />

retention volume or fraction molar mass (4,5). The contour plots allow fast<br />

orientation <strong>and</strong> identification <strong>of</strong> unwanted sample components.<br />

11 TYPICAL EXPERIMENTAL ARRANGEMENTS FOR<br />

2D-HPLC OF COMPLEX POLYMER SYSTEMS<br />

Thegeneralschemefor two-dimensionalhigh-performanceliquidchromatographic<br />

instrumentsisdepictedinFig.1.Thestrategy<strong>and</strong>conditionsforseparationcolumn<br />

(systems) selection was outlined in Secs. 2, 5, <strong>and</strong> 6. Sample transfer options were<br />

discussed in Sec. 9<strong>and</strong> some detection problems were mentioned in Sec. 10. It is<br />

evidentfromtheabovesectionsthatnouniversal2D-HPLCarrangementdoesexist.<br />

The actual setup must be tailored for each characterization task or even for each<br />

group <strong>of</strong> samples. Therefore, it is necessary to evaluate carefully relations between<br />

availableinvestment<strong>and</strong>expectedbenefits.Theinvestmentsincludemainlythecost<br />

<strong>of</strong> both method development <strong>and</strong> current measurements such as work, time,<br />

instrumentation,<strong>and</strong>material.Benefits,evidently,lieinmorepr<strong>of</strong>oundinformation<br />

about molecular characteristics <strong>of</strong> samples.<br />

The most simple 2D-HPLC includes an <strong>of</strong>f-line approach. RSR system in<br />

Fig.3isdeleted<strong>and</strong>effluentfromcolumn#1flowsdirectlyintothedetector(s)<strong>and</strong><br />

a fraction collector. Each fraction or its selected part is manually reinjected<br />

(possibly after reconcentration) into acompletely independent column (system)<br />

#2,whichisequippedwithanotherset<strong>of</strong>appropriatedetectors.Asmentioned,this<br />

approach is labor- <strong>and</strong> time-intensive. It can help in the course <strong>of</strong> scouting<br />

experiments.<br />

Column #1 can be operated in the stop-<strong>and</strong>-go mode. In this case, the RSR<br />

system inFig.3canbe substituted byasimplefour-porttwo-wayswitchingvalve<br />

or with asix-port two-way valve equipped with the sample loop (Fig. 17). After<br />

necessaryadjustment<strong>of</strong>experimentalconditionsforthefirstdimensionseparation<br />

system(column#1filling,mobilephase,<strong>and</strong>temperature)whichareevaluatedby<br />

detector(s) #1, effluent segments from column #1 are directed into column #2.<br />

RSR setups with the reinjection valves depicted in Figs 18 <strong>and</strong> 19 allow<br />

continuous operation <strong>of</strong> column #1; however, elution rates in column systems #1<br />

<strong>and</strong> #2 must be well matched.<br />

© 2004 by Marcel Dekker, Inc.

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