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.

The van Deemter equation was measured for different molar masses (using<br />

polystyrene st<strong>and</strong>ards in THF) over a wide molar mass range. The lower the<br />

molar mass, the more flat the dependence becomes. Even for samples beyond<br />

100,000 g/mol, very shallow flow dependence was determined. This means that<br />

these columns can be operated at higher flow rates without losing too much <strong>of</strong><br />

their efficiency.<br />

4.2.1 Precision <strong>of</strong> HighSpeed Separations<br />

Time requirement <strong>and</strong> resolution are not the only criteria for a good HighSpeed<br />

column. It should also be able to generate results with the same precision <strong>and</strong><br />

accuracy as conventional analytical columns. It should also last as long as<br />

conventional columns <strong>and</strong> should not be more expensive.<br />

Reproducibility <strong>of</strong> SEC measurements can be checked more easily by<br />

HighSpeed columns because the time requirements are much lower. This allows<br />

for better result accuracy <strong>and</strong> higher statistical security. Figure 13 shows the<br />

overlay <strong>of</strong> 10 commercial polycarbonate chromatograms in THF; every sixth run<br />

out <strong>of</strong> 60 runs in total is represented in the overlay. They overlap almost perfectly.<br />

Each run took about 2.5 min, the total run time for 60 repeats was about 2 hours.<br />

Figure 13 Overlay <strong>of</strong> 10 (out <strong>of</strong> 60) repeats <strong>of</strong> a commercial polycarbonate run in THF<br />

on PSS SDV 5 mm HighSpeed, 10 3 ,10 5 A ˚ column; measured Mw ¼ (29,610 + 150) g/mol<br />

(nominal sample molar mass by producer, 30,000 g/mol).<br />

© 2004 by Marcel Dekker, Inc.

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

Saved successfully!

Ooh no, something went wrong!