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Handbook of Size Exclusion Chromatography and Related ...

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ecause <strong>of</strong> the higher relative molecular mass per unit chain length. As a result,<br />

dextrans possess larger elution volumes than polystyrenes <strong>of</strong> identical molecular<br />

weights. Proteins, more dense than r<strong>and</strong>om coils, elute as even “smaller”<br />

molecules, <strong>and</strong> their calibration curves are displaced from polystyrene <strong>and</strong><br />

dextrans <strong>of</strong> the same molecular weight. Figure 11 (83) shows this effect for<br />

calibration curves <strong>of</strong> polyethylene glycols, dextrans, <strong>and</strong> proteins on TSK-GEL<br />

SW columns containing spherical 10-mm particles with pore sizes <strong>of</strong> 130 A ˚<br />

(G2000SW), 240 A ˚ (G3000SW), <strong>and</strong> 450 A ˚ (G4000SW). The data in Fig. 11<br />

emphasize that calibration should occur with st<strong>and</strong>ards possessing the same shape<br />

<strong>and</strong> hydrodynamic volume characteristics as the solute.<br />

Several references have outlined the various methodologies for obtaining<br />

correct calibration curves (8,17,18,45,84,85). The simplest is the peak position<br />

calibration method. It can be used for macromolecules that have a unique<br />

molecular weight (such as proteins) or a narrow distribution <strong>of</strong> molecular<br />

weights. The logarithm <strong>of</strong> the molecular weight for a series <strong>of</strong> known molecular<br />

weight st<strong>and</strong>ards (MW=MN 1:1, where MW <strong>and</strong> MN are the weight- <strong>and</strong><br />

number-average molecular weights) is plotted vs. their elution volumes. In the<br />

Figure 11 Calibration curves for proteins (closed circles), polyethylene glycols (open<br />

circles), <strong>and</strong> dextrans (half-closed circles). Columns, TSKgel SW, 10mm, 60cm 7.5mm,<br />

two in series. (A) G2000SW, (B) G3000SW, (C) G4000SW. Mobile phase, proteins: 0.1 M<br />

phosphate, pH 7, þ0.3 M sodium chloride; dextrans <strong>and</strong> polyethylene glycols: distilled<br />

water; flow rate, 1.0mL/min; detection, 220nm, UV.<br />

© 2004 by Marcel Dekker, Inc.

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