Separation and Characterization of Highly Charged Polyelectrolytes Using Free-Solution Capillary Electrophoresis

Area of Science:

• Polymer Chemistry
• Analytical Chemistry
• Physical Chemistry

Background:

• Characterizing statistical copolymers with varying charge densities is analytically challenging.
• Polyelectrolyte (PE) electrophoretic mobility plateaus due to Manning counterion condensation.
• Overcoming Manning condensation limits is crucial for advanced polymer analysis.

Purpose of the Study:

• To demonstrate high-resolution separation of charged PEs beyond Manning condensation limits.
• To analyze statistical poly(acrylamide-co-2-acrylamido-2-methylpropanesulfonate) copolymers.
• To investigate the impact of ionic strength on PE separation and mobility.

Main Methods:

• Free-solution capillary electrophoresis (CE) in counter electroosmotic mode.
• Systematic variation of background electrolyte (BGE) ionic strength.
• Modeling of electrophoretic mobility dependence on ionic strength.

Main Results:

• Achieved full separation of nine PE samples with charge densities from 3% to 100%.
• Observed asymmetric charge density distributions in highly charged PEs, linked to copolymerization reactivity.
• Demonstrated that increased BGE ionic strength enhances resolution by matching EOF and PE mobility, and increasing mobility's charge density dependence.

Conclusions:

• Free-solution CE can achieve high-resolution separations of charged PEs irrespective of Manning condensation.
• BGE ionic strength is a critical parameter for optimizing PE separation resolution.
• The study provides insights into PE separation mechanisms and copolymer characterization.