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Handbook of Size Exclusion Chromatography and Related ...

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Figure 8 Column performance <strong>of</strong> short wide-bore SEC column with 20 mm internal<br />

diameter <strong>and</strong> 50 mm length (sample <strong>and</strong> conditions similar to Fig. 3).<br />

The separation efficiency is not as good as in the case with aconventional<br />

column. It could be shown (6) that this is related to the nonoptimized flow pr<strong>of</strong>ile<br />

inside the column <strong>and</strong> is not related to wall effects. Influence <strong>of</strong> the wall will,<br />

however, be aparameter affecting the efficiency <strong>of</strong> the separation when columns<br />

are further reduced in length.<br />

Aquantitativeinvestigation<strong>of</strong>columnperformanceshowedthatthespecific<br />

resolution <strong>of</strong> 4.3 is about 20% lower than on aconventional column. The plate<br />

count is influenced even more: using BHT as a probe molecule only<br />

58,500 plates/m could be measured (using the ISO 13385 test) as compared to<br />

92,500 for the conventional column.<br />

3.2 Evaluation <strong>of</strong> Different High-Speed Column<br />

Design Approaches<br />

The performance <strong>of</strong> different column designs with regard to key criteria in<br />

macromolecular separations such as resolution, porevolume, <strong>and</strong> peak symmetry<br />

are summarized in Table 3.<br />

The available pore volume in an SEC column directly determines peak<br />

resolution<strong>and</strong>separationefficiency,whiletheflowratesettingwillinfluenceshear<br />

degradation <strong>of</strong> the sample, the effective mass transfer, <strong>and</strong> consequently<br />

resolution.<br />

Figure 9compares the raw chromatograms <strong>of</strong> different column designs<br />

under identical experimental conditions using the same volume flow rate. The<br />

deterioration <strong>of</strong> column efficiency at identical volume flow is directly related to<br />

columns with low pore volume (see chromatograms [2] <strong>and</strong> [3] in Fig. 9), that is,<br />

© 2004 by Marcel Dekker, Inc.

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