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Handbook of Size Exclusion Chromatography and Related ...

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Figure 21 Comparisons <strong>of</strong> apparent molecular size as determined by intrinsic viscosity<br />

(IV) <strong>and</strong> refractive index (RI) detectors.<br />

average size but collectively appear to be very large molecules. Amass detector<br />

may determine how much material is in the form <strong>of</strong> large particles but does not<br />

reveal the true size <strong>of</strong> the particles’ component molecules. If different asphalts<br />

form molecular associations to different degrees, then it is pointless to draw<br />

conclusions on asphalt molecular size distributions purely from SEC.<br />

7 SUMMARY<br />

<strong>Size</strong> exclusion chromatography has been used extensively for the study <strong>of</strong><br />

asphalts. Conditions that have been reported in the literature are summarized<br />

in Table 5. SEC <strong>of</strong> asphalts is especially useful for observing differences between<br />

asphalts, changes that occur to an asphalt upon oxidative aging, <strong>and</strong> for detecting<br />

low molecular size contaminants. Correlations <strong>of</strong> SEC chromatograms with<br />

physicalproperties,althoughaggressivelysought,havebeenelusive,undoubtedly<br />

because<strong>of</strong>therole<strong>of</strong>otherfactorsbesidessize,suchasthechemicalnature<strong>of</strong>the<br />

molecules <strong>and</strong> the compatibility <strong>of</strong> the many components in the asphalt blend.<br />

© 2004 by Marcel Dekker, Inc.

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