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Handbook of Size Exclusion Chromatography and Related ...

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Figure 21 Wheat glucan. Elution pr<strong>of</strong>ile triplet: mass by DRI !raw mass ev (—B—)<br />

[Eqs (6) <strong>and</strong> (7)]. Viscosity: inlet pressure ! raw ip (—O—). Viscosity: differential<br />

pressure ! raw dp (—X—). SEC system: TosoHaas guard PWH þ GMPWM þ<br />

GMPW6000 þ 5000 þ 4000 þ 3000 (150 7.5 mm); eluent, 0.1 M NaCl(aq) þ<br />

0.005 M Na2CO3(aq) þ NaN3; flow rate, 0.80 mL/min, sample (injected) volume,<br />

0.4 mL (5 mg/mL).<br />

5.3.4 Mass/Molar: Absolute Molecular Weight Distribution<br />

Toobtain the true molecular weight <strong>of</strong> constituting glucans for astarch sample<br />

without perturbing influences <strong>of</strong> aggregates, the number <strong>of</strong> molecules, as well as<br />

theirmass,isrequired.Molarconcentration(number<strong>of</strong>molecules)forstarchglucans<br />

may be achieved by quantitative pyridylamination (PA) <strong>of</strong> the terminal reducing<br />

OH-group <strong>and</strong> vis-spectroscopy <strong>of</strong>formed PA-glucans (69–71) (Fig. 23).<br />

SEC combined with universal mass detection by an interferometric DRI<br />

detector (DRI !mass ev) <strong>and</strong> detection <strong>of</strong> the chromophor with afluorescence<br />

detector (lex ¼315 nm; lem ¼400 nm) (fluorescence !mol ev) (Fig. 24)<br />

enables computation <strong>of</strong> absolute molecular weights [Eqs (21) <strong>and</strong> (22)] without<br />

theinfluence<strong>of</strong>aggregatesasthereisgoodbasisfortheassumptionthatindividual<br />

as well as associated glucans are derivatized.<br />

Mi ¼ ci[g=L]<br />

ni[mol=L] ¼<br />

raw MWV ¼lg<br />

g<br />

mol i<br />

mass ev<br />

mol ev<br />

(21)<br />

(22)<br />

Figure 25a illustrates the results indicating that molecular weight <strong>of</strong> constituting<br />

wheatstarchglucansisintherange<strong>of</strong>several10 5 g/mol(Figs25b,c),whichisat<br />

© 2004 by Marcel Dekker, Inc.

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