Separation and migration behavior of structurally related phenothiazines in cyclodextrin-modified capillary zone electrophoresis

The influences of buffer pH and the concentration of β-cyclodextrins (β-CDs) on the separation and migration behavior of 13 structurally related phenothiazines in CD-modified capillary zone electrophoresis (CD-CZE) using a phosphate background electrolyte at low pH were investigated. We focused on the separation of these phenothiazines, including the enantiomers of chiral analytes, with the use of β-CD and hydroxypropyl-β-CD (HP-β-CD) as electrolyte modifiers or chiral selectors at concentrations less than 8 mM. The results indicate that the interactions of phenothiazines with β-CDs are very strong and that effective separations of 13 analytes can be achieved with addition of 0.3 mM β-CD or 0.5 mM HP-β-CD in a phosphate buffer at pH 3.0. Binding constants of phenothiazines to β-CDs were evaluated for a better understanding of the interactions of phenothiazines with β-CDs.