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Handbook of Size Exclusion Chromatography and Related ...

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groupsonPVP/DMAEMAareresponsibleforthecationicchargeinapH 7buffer.<br />

Because <strong>of</strong> the cationic charges on the molecules, amuch higher salt content is<br />

needed in the SEC mobile phase for the cationic PVP/DMAEMA copolymers<br />

(0.5 MLiNO3)thanthesaltcontentsfornonionic<strong>and</strong>anioniccopolymers(0.1<strong>and</strong><br />

0.2 MLiNO3) to improve separation <strong>and</strong> recovery <strong>of</strong> polymer. As indicated in the<br />

earlier discussions, these semirigid polymeric gels are hydroxylated PMMA in<br />

nature. They can be expected to have asmall amount <strong>of</strong> free carboxyl groups on<br />

the gels as aresult <strong>of</strong> hydrolysis, which can interact adversely with the cationic<br />

polymers. The much higher salt content (0.5 M) is required to neutralize the<br />

electrostaticinteractionsbetweenthecationicpolymer<strong>and</strong>thecarboxylategroups<br />

onthecolumn.A100%recovery<strong>of</strong>thecationicPVP/DMAEMAwasachievedin<br />

SEC in the pH 7(0.5 MLiNO3) mobile phase.<br />

Thiscationiccopolymerisalsosolubleinthe1:1(vol/vol)water–methanol<br />

mobile phase with 0.1 Mlithium nitrate, <strong>and</strong> SEC has been carried out in the past<br />

in this laboratory in this mobile phase with the Ultrahydrogel columns, with<br />

adequate results. The separation <strong>and</strong> recovery are generally better in the pH 7<br />

buffer with 0.5 Mlithium nitrate than in thewater–methanol mixed mobile phase<br />

with 0.1 Mlithium nitrate with the Ultrahydrogel columns <strong>and</strong> therefore is the<br />

preferred method for the PVP/DMAEMA polymer.<br />

The Mark–Houwink constants K <strong>and</strong> a for cationic PVP/DMAEMA<br />

copolymersinpH 7bufferweredeterminedas1.42 10 24 <strong>and</strong>0.67,respectively.<br />

The intrinsic viscosities <strong>and</strong> absolute molecular weights <strong>of</strong> PVP/DMAEMA are<br />

shown in Table 9. The number-average molecular weights are overestimated by<br />

SEC/LALLS. The weight-average molecular weights determined by SEC/<br />

LALLS are the same as those determined by SEC with universal calibration,<br />

indicating the cationic PVP/DMAEMA copolymers are separated by hydrodynamic<br />

volumes in SEC. The overlays <strong>of</strong> molecular weight distributions <strong>of</strong> the<br />

cationic PVP/DMAEMA copolymers are shown in Fig. 11.<br />

Table 9 Intrinsic Viscosities <strong>and</strong> Absolute Molecular Weights <strong>of</strong> Cationic PVP/<br />

DMAEMA Copolymers in pH 7 Buffer, 0.5 M LiNO3<br />

Polymer<br />

Absolute molecular weights (AMU)<br />

SEC/LALLS SEC-universal calibration<br />

Intrinsic<br />

viscosities Mw Mn Mw Mn<br />

734 0.647 300,000 115,000 331,000 110,000<br />

755 2.15 1,630,000 704,000 1,720,000 483,000<br />

755N 2.22 2,020,000 889,000 2,020,000 523,000<br />

Source: From Ref. 6.<br />

© 2004 by Marcel Dekker, Inc.

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