Investigation of polymer−surfactant complexes by both micellar solubilization and pre-column derivatization capillary electrophoresis

Abstract

“Pseudo-polyanions” are formed in some mixtures of nonionic water-soluble polymers and anionic surfactants with ultraviolet (UV) absorption signals, which is verified by capillary electrophoresis (CE) equipped with an UV detector. However, it is still unclear whether two typical mixtures of PEG (polyethylene glycol)−LDS (lithium dodecylsulfate) and PEG−SDS (sodium dodecylsulfate) are pseudo-polyanions or not due to lack of necessary UV absorption. Therefore, with the help of UV probes or UV labeling reagents, micellar solubilization CE and pre-column derivatization CE are implemented to make the mixtures detectable or “visible” by a UV detector. Experimental results show that both PEG–LDS and PEG–SDS complexes are pseudo-polyanions verified by the above strategies. Combined with previous works, most mixtures of nonionic water-soluble polymers and anionic surfactants can form unique pseudo-polyanions by dint of ion bridge no matter whether with or without UV absorption. What’s more, the bridging-to-diffusion ion ratio and the charge-to-size ratio of pseudo-polyanions are dominated by the bridging ions, and the smaller the hydrated ionic radius (H+ < K+ < Na+ < Li+) is, the stronger the polyanion nature is.