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

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Figure 2 Partition coefficients KL <strong>and</strong> KH (solid lines) <strong>of</strong> short <strong>and</strong> long chains (20 <strong>and</strong><br />

100 beads) in an equal-mass mixture in a good solvent with a slit <strong>of</strong> width 6 (unit<br />

length ¼ lattice unit), plotted as a function <strong>of</strong> the total volume fraction f E <strong>of</strong> the chains in<br />

the surrounding unconfined space. The partition coefficients for solutions <strong>of</strong> monodisperse<br />

polymer, namely a solution <strong>of</strong> the short chains only <strong>and</strong> a solution <strong>of</strong> the long chains only,<br />

are drawn as dotted lines. (From Ref. 16.)<br />

partition coefficients <strong>of</strong> long <strong>and</strong> short chains, KH <strong>and</strong> KL, are plotted as a<br />

function <strong>of</strong> the total volume fraction f E <strong>of</strong> the chains in the surrounding solution.<br />

Overlapping <strong>of</strong> chains occurs at around f E ¼ 0:40, 0.12, <strong>and</strong> 0.19 in solutions <strong>of</strong><br />

short chains only, long chains only, <strong>and</strong> their mixture, respectively. At low<br />

concentrations, each component <strong>of</strong> the polymer is partitioned independently.<br />

Therefore, a pair <strong>of</strong> dashed <strong>and</strong> solid lines share the intercept. With a slight<br />

increase in f E, KL rises rapidly, whereas KH remains near zero until f E reaches<br />

the overlap concentration. The increase in KL occurs at concentrations well below<br />

the overlap concentration. Enhancement <strong>of</strong> KL <strong>and</strong> suppression <strong>of</strong> KH compared<br />

with the monodisperse counterparts are evident: the solid line <strong>of</strong> KL for the short<br />

chains runs above the curve for the monodisperse system <strong>of</strong> short chains; the<br />

solid line <strong>of</strong> KH for the long chains runs below the curve for a monodisperse<br />

system <strong>of</strong> long chains. KL exceeds one, <strong>and</strong> the disparity between KL <strong>and</strong> KH is<br />

greater compared with independent partitioning <strong>of</strong> each component. If the long<br />

chains are longer <strong>and</strong> the short chains are shorter, the disparity between KL <strong>and</strong><br />

KH in Fig. 2 will be greater.<br />

As in HPLC, a greater KL KH leads to a greater difference between<br />

retention times <strong>of</strong> the two components. The separation resolution is better when<br />

the injected solution is concentrated, rather than dilute. SEC, however, does not<br />

make use <strong>of</strong> this principle, because universality, as represented by the SEC<br />

calibration curve, fails at high concentrations. When the purpose <strong>of</strong> separation is<br />

© 2004 by Marcel Dekker, Inc.

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

Saved successfully!

Ooh no, something went wrong!