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Handbook of Size Exclusion Chromatography and Related ...

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(between 0.5 <strong>and</strong> 1.5 mL/min). Higher or lower flow rates will lead to inferior<br />

performance. This can be explained by the van Deemter equation, which relates<br />

plate height, h, with the linear flow rate, u:<br />

h¼Aþ B<br />

u þCu<br />

whereArepresents the eddy diffusion term(Fig.4), whichmainly depends on the<br />

particle size, B is related to longitudinal diffusion effects, which are not very<br />

prominent in densely packed SEC columns, <strong>and</strong> C is the so-called mass transfer<br />

term, which describes (in a simple analogy) the movement <strong>of</strong> the solute between<br />

the mobile <strong>and</strong> stationary phase. The higher the linear flow velocity the more<br />

difficult it will get for the solutes to penetrate the pores <strong>of</strong> the packing <strong>and</strong> the<br />

lower the resolution will be.<br />

4.1 Properties <strong>of</strong> PSS HighSpeed TM SEC Columns<br />

Because parallelization <strong>of</strong> SEC analyses did not meet the requirements PSS set for<br />

optimal implementation <strong>and</strong> easy use <strong>of</strong> fast SEC analyses, PSS decided to design<br />

SEC packing materials that allow the true high-speed separations. The design <strong>of</strong><br />

new SEC packing materials requires a lot <strong>of</strong> experience from synthetic chemists on<br />

copolymerization <strong>and</strong> network formation as well as from analytical chemists who<br />

have to test that the design criteria are met (10).<br />

Every change in column packing materials is critical for the manufacturer<br />

(market acceptance) <strong>and</strong> for the users (method compatibility). Therefore the key<br />

requirement for PSS HighSpeed SEC packings has been the trouble-free method<br />

transfer from an existing conventional application to a PSS HighSpeed<br />

application. The only thing a PSS HighSpeed user should have to do is replace<br />

a conventional column with a similar HighSpeed column. This is only possible if a<br />

number <strong>of</strong> other design criteria are met:<br />

. SEC separations must be possible in 1 min,<br />

. There must be no change in sample separation ranges, resolution, <strong>and</strong><br />

efficiency,<br />

. The column must run on already existing instrumentation (no need for<br />

special equipment),<br />

. There must be simple transfer <strong>of</strong> existing methods (one-to-one column<br />

exchange),<br />

. All packings must be available in conventional <strong>and</strong> HighSpeed types,<br />

. The same samples must be able to be run as before (no shearing, high<br />

efficiency, <strong>and</strong> so on),<br />

. Existing SEC instruments must be utilized more efficiently (no need to<br />

buy new equipment with increasing sample numbers), <strong>and</strong><br />

© 2004 by Marcel Dekker, Inc.

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