Handbook of Size Exclusion Chromatography and Related ...

Figure 16 Wheat glucan. Normalized DRI elution profiles !mass ev [Eqs. (6) and
(7)]. Universal SEC calibration constructed from: dextran SEC calibration þ
SMH K ¼ 0.0978 mL/g, SMH a ¼ 0.500.
absolute molecular weight distribution (m MWD d, n MWD d) and degree
of polymerization distribution (m dpD d, n dpD d) may be computed.
Although such molecular weights are assigned as absolute, due to
superimposed glucan aggregates that dominate the scattering signal, these
molecular weights for starch glucans are apparent absolute molecular weights.
With the elution profile of Excess–Rayleigh factors [Eq. (12)] and
information about glucan concentration for each SEC separated fraction, a
normalized scattering profile for scattering angle u(e.g., u¼58 !LS 5 EV)
may be established [Eq. (13)] with area equivalent to weight-average molecular
weight (Mw) according to Eq. (14) (Fig. 19a).
Ru ¼ Pu
raw LS 5
att const !R 5¼
P(0)
raw LS 0
LS 5 EV ¼
Mw raw ¼
R 5mass ev
koptconc
ð int stop
int start
(12)
(13)
LS 5 EV (14)
Therawdatascatteringprofile(Fig.18)aswellasthenormalizedscattering
profile (Fig. 19a) illustrate the presence of aggregates below the detection limit
© 2004 by Marcel Dekker, Inc.