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Handbook of Size Exclusion Chromatography and Related ...

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The second most important element <strong>of</strong> multi-angle measurements is their<br />

built-in redundancy.In the event that any detector became unusable <strong>and</strong> whose<br />

results, therefore, had to be discarded (a failed photodiode because <strong>of</strong> electrical<br />

problems, solution-borne obstructions that may block the scattered light from<br />

certain detectors, <strong>and</strong> so on), the deletion <strong>of</strong> one or more such detector signals<br />

fromthefinalanalysiswouldhaveafarsmallereffectontheresultantcalculations<br />

becausetherewouldbesomanyadditionaldetectorstocompensateforanylosses.<br />

Finally,with measurementsspanningabroad range <strong>of</strong>scatteringangles,the<br />

ability to measure larger particles whose scattering characteristics show much<br />

steeper, <strong>and</strong>/or nonlinear behavior with scattering angle is enhanced by the<br />

presence <strong>of</strong> more detector angles.<br />

Let us consider asimple comparison <strong>of</strong> so-called “clean” chromatography<br />

with “poor” chromatography: the distinction related qualitatively to the<br />

contributions <strong>of</strong> noise to the signals. (See also the discussion <strong>of</strong> Sec. 5.) The<br />

sources <strong>of</strong> noise could be the shedding <strong>of</strong> the separation columns, the careless<br />

preparation<strong>of</strong>thesamples,faulty mobilephase filtering,degassingproblems,<strong>and</strong><br />

soon.Figure12showstheexcessRayleighratiosmeasuredfromasample<strong>of</strong>aciddegraded<br />

amylopectin, which resulted in very clean signals at all detectors. The<br />

trace labeled AUX corresponds to the DRI detector (corrected for the delay<br />

volumebetweenit<strong>and</strong>theMALSunit.Figure13showstheresultantfitsatasingle<br />

Figure 12 Three-dimensional plot <strong>of</strong> excess Rayleigh ratios as a function <strong>of</strong> elution<br />

volume for “good” chromatography: one trace for each scattering angle.<br />

© 2004 by Marcel Dekker, Inc.

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