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Handbook of Size Exclusion Chromatography and Related ...

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Table 4 Molecular Weights <strong>of</strong> PVP Determined by SEC/LALLS <strong>and</strong> SEC with<br />

Universal Calibration<br />

Grade SEC/LALLS<br />

K-15 1.68 10 4<br />

K-30 6.24 10 4<br />

K-60 3.37 10 5<br />

K-90 1.52 10 6<br />

Source: From Ref. 4.<br />

Mw<br />

Universal<br />

calibration SEC/LALLS<br />

1.12 10 4<br />

6.19 10 4<br />

3.40 10 5<br />

1.24 10 6<br />

1.10 10 4<br />

3.10 10 4<br />

1.57 10 5<br />

6.38 10 5<br />

Thisoverestimationisexpectedtobemoresignificantforthebroadmolecularweight<br />

distributionpolymersthanforthenarrowdistributionpolymers.Thelargerdifference<br />

in M wfor PVP K-15 (vis-à -vis the higher K-value grades) could be caused by a<br />

combination <strong>of</strong> lower sensitivity <strong>of</strong> LALLS at low molecular weight <strong>and</strong>/or less<br />

accuracy<strong>of</strong>theuniversalcalibrationcurveatthelow-molecular-weightend.Absolute<br />

molecularweightdistributionsforPVPK-90,K-60,K-30,<strong>and</strong>K-15gradesbasedon<br />

universal calibration are shown in Fig. 1.<br />

3.3 SEC <strong>of</strong> Commercial Grades <strong>of</strong> PVP with aSingle<br />

Linear Column<br />

One<strong>of</strong>themostimportantdevelopmentsinthetechnology<strong>of</strong>semirigidpolymeric<br />

gelsforSEC<strong>of</strong>syntheticwater-solublepolymersinrecentyearsistheavailability<br />

<strong>of</strong>thelog-linearcolumnwithgoodseparationrange,fromlessthan1000toseveral<br />

millioninmolecularweight.Alinearcalibrationcurveimprovesboththeaccuracy<br />

<strong>and</strong> precision <strong>of</strong> the determination <strong>of</strong> molecular weight <strong>and</strong> molecular weight<br />

distribution. The commonly used br<strong>and</strong> names for linear columns for aqueous<br />

SEC are Showa Denko Shodex OH pack, Toyo Soda TSK-PW, <strong>and</strong> Waters<br />

Ultrahydrogel. The column packing materials for these columns are all<br />

crosslinked, hydroxylated polymethyl methacrylate (PMMA) in nature. Using<br />

singlelinearcolumns alsogreatlyreduces analysistime <strong>and</strong>solventconsumption,<br />

making SEC apractical method for quality assurance.<br />

Linear PEO calibration curves generated in this laboratory for the<br />

Ultrahydrogel linear column in 20:80 methanol–water (vol/vol) with 0.1 M<br />

lithium nitrate <strong>and</strong> in 50:50 methanol–water (vol/vol) with 0.1 Mlithium nitrate<br />

<strong>and</strong> for the Shodex KB-80M linear column in 20:80 methanol–water with 0.1 M<br />

lithiumnitrateareshowninFigs2,3,<strong>and</strong>4.Theeffect<strong>of</strong>methanol–waterratio<strong>of</strong><br />

© 2004 by Marcel Dekker, Inc.<br />

Mn<br />

Universal<br />

calibration<br />

4.18 10 3<br />

1.28 10 4<br />

5.23 10 4<br />

2.06 10 5

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