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Handbook of Size Exclusion Chromatography and Related ...

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Figure 17 Wheat glucan. Sphere equivalent radii distribution (ReD) <strong>of</strong> SEC-separated<br />

wheat glucans. Differential mass fractions: m R eD d(—4—) [Eq. (11)]. Differential molar<br />

fractions: n ReD d(—A—) [Eq. (11)].<br />

<strong>of</strong> the mass detector but with huge molar masses. Scattering in general, <strong>and</strong><br />

low-angle scattering in particular, is enormously sensitive to aggregates (the signal<br />

is proportional to the coherent segment length with the power <strong>of</strong> 6) <strong>and</strong> thus LSsignals<br />

are dominated by minimum amounts <strong>of</strong> huge molecules or aggregates.<br />

However, absolute molecular weight calibration (raw MWV) for the mass <strong>and</strong><br />

scattering pr<strong>of</strong>iles is obtained using Eqs (15) <strong>and</strong> (16), <strong>and</strong> if applied to each<br />

fraction, absolute molecular weight calibration is achieved.<br />

Kc<br />

RQ c!0<br />

Q!0<br />

¼ 1<br />

þ 2A2c (15)<br />

Mw<br />

" # 1<br />

Kc<br />

Mw ¼<br />

2A2c ! log (M) vs. Vret<br />

RQ c!0<br />

Q!0<br />

(16)<br />

which can be done by simply computing the ratio <strong>of</strong> normalized scattering <strong>and</strong><br />

mass pr<strong>of</strong>iles <strong>and</strong> taking the logarithm <strong>of</strong> the result [Eq. (17)].<br />

© 2004 by Marcel Dekker, Inc.<br />

raw MWV ¼ log<br />

LS 5 EV<br />

mass ev<br />

(17)

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