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Handbook of Size Exclusion Chromatography and Related ...

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Figure 18 Elution pr<strong>of</strong>ile <strong>of</strong> some fibroblast growth factor multimers. Two dimer forms<br />

with identical mass elute at different times.<br />

Numerous studies have been presented in the literature confirming the<br />

absolutemeasurementcapability<strong>of</strong>MALS.Proteinsinparticularhavebeenuseful<br />

examples <strong>of</strong> such validation since many protein masses are known apriori from<br />

sequence<strong>and</strong>aminoacid<strong>and</strong>carbohydratecomposition.Jiuetal.haveshown(31)<br />

good agreement for MALS-derived results <strong>of</strong> protein complexes with both<br />

sedimentation equilibrium <strong>and</strong> molar masses calculated from amino acid <strong>and</strong><br />

carbohydrate composition. Li et al. have compared (32) MALS results with small<br />

angle x-ray scattering <strong>and</strong> calculated masses for some chimeric proteins. Another<br />

powerful comparison (33) was carried out by Singer et al., wherein the authors<br />

report acomparison <strong>of</strong> MALS with analyses <strong>of</strong> similar molecules by SDS-PAGE,<br />

SE, <strong>and</strong> MALDI-TOF mass spectroscopy.<br />

Although at this time, the only commercial MALS systems that may be<br />

coupled to chromatographs are the DAWN w detectors <strong>of</strong> Wyatt Technology<br />

Corporation,therecanbelittledoubtthatintheyearsaheadtherewillbeothers.A<br />

seven-angledetectorhasbeenintroducedbyBrookhavenInstrumentsCorporation<br />

(Holtsville, New York), though no published chromatography results have been<br />

seen at the time <strong>of</strong> this writing. Two-angle light-scattering detection systems are<br />

manufactured by both Precision Detectors, Inc. (Bollingham, Massachusetts) <strong>and</strong><br />

Viscotek,Inc.(Houston,Texas).Bothareavailableinsingle908anglemodeswith<br />

application to small molar mass samples, although the former actually collects<br />

scattered light over a broad range <strong>of</strong> scattering angles about 908 (detector<br />

acceptancesolidangle reportedbythemanufacturer (34) as0.8steradians!).Both<br />

requirecalibrationtoknownmolarmassst<strong>and</strong>ardsforeachmobilephaseused(see<br />

Sec. 6).<br />

In recent years, photon correlation spectroscopy (also known as quasi-elastic<br />

light scattering QELS, inelastic light scattering, dynamic light scattering, <strong>and</strong> so<br />

© 2004 by Marcel Dekker, Inc.

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