Desvignes Isabelle, Chamieh Joseph, Cottet Hervé
Institut des Biomolécules Max Mousseron, University of Montpellier, CNRS, ENSCM, 34095 Montpellier, France.
Polymers (Basel). 2018 Dec 2;10(12):1331. doi: 10.3390/polym10121331.
The characterization of statistical copolymers of various charge densities remains an important and challenging analytical issue. Indeed, the polyelectrolyte (PE) effective electrophoretic mobility tends to level off above a certain charge density, due to the occurrence of Manning counterion condensation. Surprisingly, we demonstrate in this work that it is possible to get highly resolutive separations of charged PE using free-solution capillary electrophoresis, even above the critical value predicted by the Manning counterion condensation theory. Full separation of nine statistical poly(acrylamide-co-2-acrylamido-2-methylpropanesulfonate) polymers of different charge densities varying between 3% and 100% was obtained by adjusting the ionic strength of the background electrolyte (BGE) in counter electroosmotic mode. Distributions of the chemical charge density could be obtained for the nine PE samples, showing a strong asymmetry of the distribution for the highest-charged PE. This asymmetry can be explained by the different reactivity ratios during the copolymerization. To shed more light on the separation mechanism, effective and apparent selectivities were determined by a systematic study and modeling of the electrophoretic mobility dependence according to the ionic strength. It is demonstrated that the increase in resolution with increasing BGE ionic strength is not only due to a closer matching of the electroosmotic flow magnitude with the PE electrophoretic effective mobility, but also to an increase of the dependence of the PE effective mobility according to the charge density.
各种电荷密度的统计共聚物的表征仍然是一个重要且具有挑战性的分析问题。实际上，由于曼宁反离子凝聚的发生，聚电解质（PE）的有效电泳迁移率在一定电荷密度以上趋于平稳。令人惊讶的是，我们在这项工作中证明，即使在曼宁反离子凝聚理论预测的临界值以上，使用自由溶液毛细管电泳也能够对带电的PE进行高分辨率分离。通过在反向电渗模式下调节背景电解质（BGE）的离子强度，实现了电荷密度在3%至100%之间变化的九种不同电荷密度的统计聚（丙烯酰胺 - 共 - 2 - 丙烯酰胺基 - 2 - 甲基丙烷磺酸盐）聚合物的完全分离。可以获得九个PE样品的化学电荷密度分布，结果表明，电荷密度最高的PE的分布具有很强的不对称性。这种不对称性可以通过共聚过程中不同的反应比来解释。为了更深入地了解分离机制，通过对电泳迁移率随离子强度的依赖性进行系统研究和建模，确定了有效选择性和表观选择性。结果表明，随着BGE离子强度的增加分辨率提高，这不仅是由于电渗流大小与PE有效电泳迁移率更紧密匹配，还归因于PE有效迁移率随电荷密度的依赖性增加。
