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Handbook of Size Exclusion Chromatography and Related ...

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Figure 15 Wheat glucan. Dextran equivalent normalized molecular weight distribution.<br />

Differential mass fractions: m MWD d(—4—) [Eq. (8)], differential molar fractions:<br />

n MWD d(—A—) [Eq. (9)]. Dextran equivalent molecular weight averages: M n: number<br />

average, 256,600 g/M; Mw: weight-average, 1,295,000 g/M polydispersity: Mw/Mn: 5.06.<br />

SECseparatedfractionsVe,i<strong>and</strong>distributioneitherasdistribution<strong>of</strong>massfractions<br />

(m VeD d) or molar fractions (n VeD d) according Eq. (10).<br />

Ve,i ¼ KMaþ1 i<br />

2:5NA<br />

!m VeD d^n VeD d (10)<br />

Sphere equivalent radii <strong>of</strong> excluded volume <strong>and</strong> correlated mass <strong>and</strong> molar<br />

distributions <strong>of</strong> molecule radii are computed according Eq. (11) (Fig. 17).<br />

Re,i ¼ 3Ve,i<br />

4p<br />

5.3.2 Mass/LS: Absolute Molecular Weight<br />

1 =<br />

3<br />

!m ReD d^n ReD d (11)<br />

Absolute weight-average <strong>of</strong> molecular weight (M w)<strong>of</strong> polymers can be obtained<br />

from static light-scattering experiments if sample concentration (c), specific<br />

refractive index increment (dn/dc)l, wavelength <strong>of</strong> laser light (l), experimental<br />

scattering angle (u), <strong>and</strong> ratio <strong>of</strong> intensities <strong>of</strong> applied <strong>and</strong> scattered intensity <strong>of</strong><br />

laser light (Rayleigh-factor Ru) at scattering-angle uare known. Starting from a<br />

triplet elution pr<strong>of</strong>ile (mass !raw mass, applied laser intensity !raw LS 0,<br />

scattered laser intensity !raw LS u) via several intermediates [Eqs (12)–(14)]<br />

© 2004 by Marcel Dekker, Inc.

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