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Handbook of Size Exclusion Chromatography and Related ...

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Association is such an important characteristic <strong>of</strong> asphalts, believed by<br />

many to be an indicator <strong>of</strong> asphalt performance, that attempts have been made<br />

to use poorer solvents to emphasize this feature. Unfortunately,poorer solvents<br />

lead to column fouling <strong>and</strong> bad tailing <strong>of</strong> the adsorbed material. Figure 15 is an<br />

extracted core asphalt <strong>and</strong> its Corbett fractions run in toluene <strong>and</strong> is similar to<br />

the material in Fig. 1. In both instances the asphaltenes tail badly,but in toluene<br />

this is the predominant effect, largely displacing the larger material to much<br />

lower apparent size. Similar results have also been reported for Corbett fractions<br />

in THF (140).<br />

All the evidence discussed previously indicates that if SEC is to be<br />

employed in molecular weight determinations the best solvent system for the<br />

associating material should be used. These include data at low concentrations <strong>and</strong><br />

extrapolation to infinite dilution. Elevated temperatures probably help, but the<br />

choice <strong>of</strong> solvent is especially important.<br />

There are two particularly useful schemes for choosing solvents. The oldest<br />

is the solubility parameter method <strong>of</strong> Hildebr<strong>and</strong> <strong>and</strong> Scott (141) with the<br />

modifications <strong>of</strong> Hansen <strong>and</strong> colleagues (142–144). Hildebr<strong>and</strong>’s solubility<br />

Figure 15 SEC analyses <strong>of</strong> the same samples as in Fig. 1 with a toluene carrier solvent<br />

(500A ˚ , 60cm PLgel, toluene, 1mL/min, 100mL, RI detector). The whole asphalt is<br />

analysed using a 7wt% solution; the Corbett fractions are adjusted according to their weight<br />

fraction.<br />

© 2004 by Marcel Dekker, Inc.

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