Use of the Na+ ion as an RPLC retention marker to investigate the association of dansyl amino acids with permethylated β-CD

The mechanism of binding of D, L dansyl amino acids to permethylated β-cyclodextrin (pM-βCD) has been investigated. Sodium phosphate was used as an indicator of interactions between the solutes and pM-βCD. The number (n) of sodium ions, Na+, excluded from the solute pM-βCD cavity interface when analyte transfer occurred was determined. Thesen values could be linearly correlated with the steric bulkiness of the solute. Thermodynamic data for solute transfer are discussed in relation to the extent of inclusion of the dansyl amino acids. Enthalpy-entropy compensation showed that the retention mechanism was independent of the molecular structure of the enantiomer, the configuration of the asymmetric carbon, or the concentration of salt in the mobile phase.