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Handbook of Size Exclusion Chromatography and Related ...

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Figure 3 Data for a single slice plotted with error bars.<br />

where DRj(ui;cj) is the calculated st<strong>and</strong>ard deviation <strong>of</strong> the measured excess<br />

Rayleigh ratio at ui <strong>and</strong> Dcj is the st<strong>and</strong>ard deviation <strong>of</strong> the concentration cj.<br />

Similarcalculationsareperformedtoestablishtheerrorsassociatedwiththemean<br />

square radius values.<br />

The calculations discussed briefly above are both complex <strong>and</strong> essential for<br />

any MALS determinations <strong>of</strong> molecular <strong>and</strong> particle properties. With today’s<br />

armamentarium <strong>of</strong> high-speed <strong>and</strong> low-cost computing, all the benefits <strong>of</strong> MALS<br />

should be realized by all laboratories. Most important among such benefits is the<br />

ability to judge the precision <strong>of</strong> the results reported.<br />

Avariety <strong>of</strong> other quantities essential for the characterization <strong>of</strong> molecular<br />

<strong>and</strong> particle samples must also be reported with ameasure <strong>of</strong> their precision.<br />

Once again, only by performing detailed analyses based upon the well-proven<br />

application <strong>of</strong> error propagation can MALS measurements, or for that matter any<br />

measurements, be considered avalid <strong>and</strong> reproducible technique.<br />

OtherquantitiesdeterminedfromMALSdirectlywhoseprecisionisessential<br />

includethevariousmoments<strong>of</strong>themass<strong>and</strong>sizedistributionssocalculated.Typical<br />

among them are theweight, number, <strong>and</strong> z-average molar mass (see Sec. 9). In the<br />

case <strong>of</strong> fractionated proteins, for example, the monomeric masses must be presented<br />

as precisely as possible to provide the user continuing “cold comfort” for the MALS<br />

measurement. Protein masses are generally known aprioriin any event from<br />

calculations based on DNA sequencing. References to so-called st<strong>and</strong>ards used for<br />

empirical studies are always valuable. With precision insured by reporting <strong>of</strong><br />

© 2004 by Marcel Dekker, Inc.

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