Synthesis of Cationic Diazacrown Ethers and Their Successful Application as Selectivity Modifiers in the Capillary Electrophoresis Separation of Aromatic Anions Involving Positional Isomers

Two types of positively charged diazacrown ether derivatives with different ring sizes were investigated concerning their ability as selectivity modifiers in capillary electrophoresis. The addition of the cationic diazacrowns to a migrating solution led to the successful separation of the positional isomers of naphthalenedisulfonate, naphthalenedicarboxylate, and phthalate, such that a total of eight aromatic anions were completely resolved in less than 5 minutes. The separation mechanism was studied by examining the effects of the ionic strength and the pH of the running buffer, by determining the ion-association constants between the analytes and the additives, and by elucidating their molecular structures. As a result, a combination of ion-exchange, hydrophobic interaction, and molecular geometry was found to play an important role in the observed separation behavior.