Ion-exclusion controlled size-exclusion chromatography of methacrylic acid-methyl methacrylate copolymers

Controlled ion-exclusion allows compensation of hydrophobic adsorption in s ize-exclusion chromatography of negatively charged methacrylic acid-methyl methacrylate (Eudragit) polymers using methanol as a mobile phase, Properly selected low-ionic-strength conditions below 5 mM LiCl provide correct sep aration in the size-exclusion mode. Possible disturbing effects, mainly rel ated to light scattering, under low-salt conditions are discussed and shown to be negligible if on-line concentration-light scattering detection is us ed. The absence of these disturbances is checked by a comparison of experim ents performed in methanol containing 1.25 mM and 2.5 mM LiCl. Molecular ma ss averages and distributions identical within the experimental error are o btained. (C) 2000 Elsevier Science B.V. All rights reserved.