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Handbook of Size Exclusion Chromatography and Related ...

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oadening,yetfor themostpart,ithasbeendifficulttoimplementsuchmethods.<br />

The problems associated with b<strong>and</strong> broadening are clearly shown in Fig. 7where<br />

MALS data <strong>of</strong> a BSA (bovine serum albumin) sample containing various<br />

aggregatestateshavebeenprocessed.Most<strong>of</strong>theb<strong>and</strong>broadeningarisesfromthe<br />

largedeadvolume<strong>of</strong>theDRIunitrelativetotheMALSdetector.TheMALSpeak<br />

hasbeenbroadenedbytheDRI(afterconcentration<strong>and</strong>MALSdataarecombined<br />

to calculate molar mass <strong>of</strong> the separated sample) resulting in a“grimace-like”<br />

appearance to the mass presentation instead <strong>of</strong> aflat, constant mass vs. elution<br />

volume. Figure 8 shows these same data corrected by the s<strong>of</strong>tware using a<br />

proprietary correction method developed by Steven Train<strong>of</strong>f. The monomer<br />

(largestpeak)<strong>and</strong>dimeraggregateareclearlyshowntobemonodisperse,whereas<br />

the peaks corresponding to higher aggregates clearly show (after correction for<br />

b<strong>and</strong> broadening) their unresolved polydisperse composition.<br />

Anotherimportantobject<strong>of</strong>MALSs<strong>of</strong>twarerelatestoitsh<strong>and</strong>ling<strong>of</strong>noise.<br />

Such noise, especially at very low angles, literally can overwhelm the associated<br />

signals (see Sec. 6 for additional comments.). Although careless sample<br />

preparation is <strong>of</strong>ten associated with the presence <strong>of</strong> dust or related debris affecting<br />

most the smaller scattering angles, aging columns that have begun to shed both<br />

column packing materials as well as remnants <strong>of</strong> prior samples can produce<br />

overwhelming scattering at smaller scattering angles. These contributions to noise<br />

can be especially troublesome in the presence <strong>of</strong> elutions <strong>of</strong> relatively small molar<br />

mass. If any significant filtering <strong>of</strong> such noise contributions is to be achieved by the<br />

Figure 7 Calculated molar mass vs. elution volume for a BSA sample clearly showing<br />

the effects <strong>of</strong> b<strong>and</strong> broadening.<br />

© 2004 by Marcel Dekker, Inc.

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