Oligomeric separation of ionic and nonionic ethoxylated polymers by capillary gel electrophoresis

Capillary gel electrophoresis (CGE) has proven itself as a superior, high-resolution technique for separating proteins, peptides, oligonucleotides, and other naturally occurring molecules. In the years since its inception, few applications of CGE to nonbiological synthetic polymers have been reported. CGE has been applied to the separation of ionic and nonionic ethoxylated surfactants and poly(ethylene glycol) (PEG) oligomers. Oligomer distributions of several sulfated and phosphated alkylphenol ethoxylate surfactants have been baseline resolved with CGE on commercial cross-linked polyacrylamide gel columns. Nonionic surfactants and PEG oligomers were derivatized with phthalic anhydride in order to provide charge and detectability. PEG oligomers ranging from ethylene glycol to species containing more than 120 ethylene oxide units have been resolved. A linear relationship between migration time and molecular weight was found, which indicates that the separation mechanism is not simply based on molecular size but is also influenced by the electrophoretic mobility of the oligomers. The main drawbacks of CGE include relatively long analysis times and somewhat fragile and expensive columns.