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Handbook of Size Exclusion Chromatography and Related ...

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Figure 3 <strong>Size</strong> exclusion chromatograms <strong>of</strong> low MW 90/10 wt% AM/DMDAAC<br />

copolymer with positive or negative salt peak.<br />

should be noted that the measured dn/dc <strong>of</strong> an acrylamide copolymer is an<br />

average <strong>of</strong> its components.<br />

3.2.2 SEC Analysis with RI/LALLS Dual Detectors<br />

This type <strong>of</strong> analysis provides the absolute MW <strong>and</strong> MWD without st<strong>and</strong>ards<br />

(44,46,47). The M w, M n polydispersity, <strong>and</strong> molecular weight vs. cumulative %<br />

area <strong>of</strong> polymer can be obtained. (dn/dc)T,l,m <strong>of</strong> the polymer solution should be<br />

used for MW determination. Samples characterized by this technique can be used<br />

as SEC MW st<strong>and</strong>ards.<br />

The LALLS detector is insensitive to low MW <strong>and</strong> low concentration<br />

species. Therefore, the M n determined by this method may be erroneously high.<br />

© 2004 by Marcel Dekker, Inc.

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