Molar mass characterization of cationic methyl methacrylate-ethyl acrylate copolymers using size-exclusion chromatography with online multi-angle light scattering and refractometric detection.
Size-exclusion chromatography (SEC) combined with online multi-angle light scattering (MALS) and refractometric (RI) detection has been employed for the molar mass characterisation of water-insoluble cationic methyl methacrylate-ethyl acrylate copolymers (Eudragit RS and RL). Due to their positive charge, cationic polymers are particularly difficult to separate on a SEC column, in worst cases being completely adsorbed on the oppositely charged packing material. This work has examined how a careful addition of salt (LiCl) to the copolymer solution in ethanol decreases the electrostatic interactions, clearly seen as a decrease in elution volume from the SEC column as well as an improved recovery. At a certain level of ionic strength, typically about 50 mM, the copolymer recovery from the SEC column reached 100% and molar mass distributions corresponding to the complete sample could be obtained. The combined MALS/RI detection gives the opportunity to measure the absolute molar mass independent of recovery and retention. Thus, in this study, it turned out to be a favourable tool for tracing the changes in elution behaviour of the charged copolymer as the ionic strength was increased.
Wittgren
Bengt
B
AstraZeneca R&D Mölndal, SE-431 83 Mölndal, Sweden. bengt.wittgren@astrazeneca.com
Welinder
Anette
A
Porsch
Bedrich
B
D000179:Acrylates / Q000737:chemistry*; D002412:Cations; D002850:Chromatography, Gel / Q000379:methods*; D008027:Light; D020366:Methylmethacrylate / Q000737:chemistry*; D008970:Molecular Weight; D011108:Polymers / Q000737:chemistry*; D012031:Refractometry; D012542:Scattering, Radiation
D000179:Acrylates; D002412:Cations; D011108:Polymers; D020366:Methylmethacrylate; C040833:ethyl acrylate