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Handbook of Size Exclusion Chromatography and Related ...

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on) methods, whereby the average diffusion coefficient associated with alightscattering<br />

sample is determined, have been combined with SEC chromatography<br />

to yield a characterizing diffusion coefficient at each eluting slice. If the<br />

assumption is made that the molecules being measured are spheres, the so-called<br />

hydrodynamic radius (rh)may be determined as afunction <strong>of</strong> elutionvolume. For<br />

very small molecules whose r.m.s. radius (rg) cannot be measured (that is, below<br />

about10nm),QELScanmakesuchmeasurementsdowntobelow1nm<strong>and</strong>permit<br />

conformation studies to be completed. For larger molecules, when both rh <strong>and</strong> rg<br />

may be measured, molecular conformation may be determined directly following<br />

the methods <strong>of</strong> Burchard et al. (35). The combination <strong>of</strong> MALS <strong>and</strong> QELS is<br />

expected to have very important applications for the years ahead. The DAWN<br />

instruments (Wyatt Technology Corporation) permit full MALS measurement<br />

coupled with aQELS measurement at arange <strong>of</strong> selected angles for an eluting<br />

sample. Instruments (capable <strong>of</strong> being combined with a chromatographic<br />

separation)that incorporateasingle908QELSmeasurement <strong>and</strong>single 908lightscattering<br />

measurement are manufactured by Wyatt Technology Corporation,<br />

Precision Detectors, Inc., <strong>and</strong> Protein Solutions, Inc. (Charlottesville, Virginia).<br />

Thereisahugerange<strong>of</strong>applicationsforMALSmeasurements,nottheleast<br />

<strong>of</strong> which are those listed at www.wyatt.com. This chapter has touched briefly on<br />

but a few <strong>of</strong> these applications <strong>and</strong> the significance <strong>of</strong> an integrated MALS system<br />

complete with s<strong>of</strong>tware <strong>and</strong> error analysis. There can be no doubt that Burchard<br />

<strong>and</strong> Cowie were Cass<strong>and</strong>ras when they stated that those not using MALS were at a<br />

distinct disadvantage. Unfortunately, it took almost a quarter <strong>of</strong> a century before<br />

their words began to be treated seriously.<br />

ACKNOWLEDGEMENTS<br />

Kudos to Dr. Steve Train<strong>of</strong>f for his brilliant solution <strong>of</strong> the b<strong>and</strong>-broadening<br />

problem that, in a practical sense, had remained unsolved to this day. Many thanks<br />

also to Drs. Michelle Chen <strong>and</strong> Miles Weida for their continuing contributions.<br />

REFERENCES<br />

1. W Burchard, JMG Cowie. Selected topics in polymer systems. In: MB Huglin, ed.<br />

Light Scattering from Polymer Solutions. Ch. 17:725–787, London: Academic Press,<br />

1972.<br />

2. A Einstein. The theory <strong>of</strong> opalescence <strong>of</strong> homogeneous fluids <strong>and</strong> liquid mixtures near<br />

the critical state (Theorie der Opaleszenz von homogenen Flüssigkeitsgemischen in<br />

der Nädes kritischen Zust<strong>and</strong>es). Ann Phys 33:1275–1298, 1910.<br />

3. CV Raman. Relation <strong>of</strong> Tyndall effect to osmotic pressure on colloidal solutions.<br />

Indian J Phys 2:1–6, 1927.<br />

© 2004 by Marcel Dekker, Inc.

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