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Handbook of Size Exclusion Chromatography and Related ...

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Figure 11 SEC separation <strong>of</strong> starch glucans with differences in branching pattern. At<br />

identical retention volume V ret (identical excluded volume V e) lcb-glucans typically contain<br />

less molar mass than scb-glucans.<br />

In the analysis <strong>of</strong> the elution pr<strong>of</strong>ile from SEC with respect to absolute<br />

molecular weight <strong>and</strong> excluded volume <strong>of</strong> individual glucan fractions, for<br />

identical characteristics <strong>of</strong> two glucans except differences in branching pattern<br />

different elution positions are expected: the more scb-characteristics, the later the<br />

position on the elution grid (the higher the Vret value) (Fig. 11).<br />

Although such an ideal constellation will never be found for native starch<br />

glucans, the principle however, might be useful for glucan fractions <strong>and</strong>/or glucan<br />

fragments.<br />

5.3 Analytical SEC<br />

5.3.1 Mass Detection <strong>and</strong> Calibrated Molecular Weight Distribution<br />

Elution pr<strong>of</strong>ile <strong>of</strong> mass fractions for DMSO-dissolved starch glucans from<br />

analytical SEC is obtained by in-line (differential) refractive index detection.<br />

However, total molecular dissolution <strong>of</strong> starch glucans in the concentration range<br />

around 5 mg/mL can hardly be achieved, neither in aqueous media nor in DMSO.<br />

Nevertheless, the percentage <strong>of</strong> truly dissolved glucans can be increased by a<br />

continuous dissolution process in DMSO at elevated temperature (80–908C),<br />

reflux-cooling, <strong>and</strong> permanent stirring. Monitoring <strong>of</strong> reductive potential, an<br />

indicator for the number <strong>of</strong> molecules, proved that only a negligible degradation<br />

occurs at such conditions.<br />

From the elution pr<strong>of</strong>ile area <strong>of</strong> an interferometric refractometer (area DRI)<br />

the actual glucan concentration within a selective separation range may be<br />

obtained according to Eq. (4) with known applied sample volume (loop vol),<br />

selected DRI sensitivity factor (DRI sens), previously determined DRI calibration<br />

© 2004 by Marcel Dekker, Inc.

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