28.02.2013 Views

Handbook of Size Exclusion Chromatography and Related ...

Handbook of Size Exclusion Chromatography and Related ...

Handbook of Size Exclusion Chromatography and Related ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

Figure 3 Conventional SEC chromatogram <strong>of</strong> seven polymer st<strong>and</strong>ards showing state<strong>of</strong>-the-art<br />

performance run in THF at a flow rate <strong>of</strong> 1.0 mL/min <strong>and</strong> at ambient temperature.<br />

very good resolution across the total molar mass range. The peaks are very well<br />

separated from the solvent peaks. The shape <strong>of</strong> all the peaks is symmetrical,<br />

indicatingahomogeneouslypacked columnbed.Thereisnoindication<strong>of</strong>sample<br />

degradation in the high molar mass regime. The number <strong>of</strong> theoretical plates for<br />

BHT was calculated as 92,500 plates/m <strong>and</strong> the specific resolution was 5.2<br />

[determinedaccordingtoISO13885st<strong>and</strong>ard(9)].Theseareverygoodvaluesfor<br />

a mixed-bed column indicating a perfect system for efficient <strong>and</strong> reliable<br />

separations <strong>and</strong> molar mass calculations.<br />

3.1.2 Increasing Eluent Flow Rate<br />

BecauseSECisbasedonthediffusion<strong>of</strong>moleculesbetweenamobilephase<strong>and</strong>a<br />

stagnantmobilephaseintheporestructure<strong>of</strong>thepacking,theeluentflowratewill<br />

influence the efficiency <strong>of</strong> the separation. This is avery well-known <strong>and</strong> wellunderstood<br />

phenomenon, which can be described by the van Deemter relation<br />

(Fig. 4). The efficiency <strong>of</strong> the separation is expected to drop continuously with<br />

increased linear flow velocity (the speed <strong>of</strong> the solvent front that travels along the<br />

column).<br />

In order to underst<strong>and</strong> visually the importance <strong>of</strong> the linear flow rate on<br />

separation efficiency,the experiment with the conventional column was repeated<br />

at aflow rate <strong>of</strong> 4.0 mL/min instead <strong>of</strong> 1.0 mL/min (above). Figure 5shows the<br />

© 2004 by Marcel Dekker, Inc.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!