Determination of formation constants for .beta.-cyclodextrin complexes of anthracene and pyrene using reversed-phase liquid chromatography

The stoichlometry and apparent formation constants of anthracene and pyrene β-cyclodextrln (β-CD) complexes were determined by use of liquid chromatography. These values were measured in mobile-phase mixtures of methanol-water and in the same mixtures modified with 1 % v/v tort-butyl alcohol or cyclopentanol. The results show that anthracene forms a 1:1 complex with β-CD, and the apparent formation constant (K1) values in mobile-phase mixtures of 55 % v/v, 60% v/v, and 65% v/v methanol-water are 373, 242, and 136 M-1, respectively. Modification of the mobile-phase mixtures with 1% v/v tert-butyl alcohol or cyclopentanol produced a slight decrease in the anthracene K1 values. Pyrene exhibited prohibitively long retention times in the 55% v/v methanol-45 % v/v water mixture and also showed little interaction with β-CD in 60% v/v and 65% v/v methanol-water mixtures. However, a remarkable change in capacity factor was observed for pyrene in the presence of 1 % v/v tert-butyl alcohol or cyclopentanol. A stoichiometric ratio of 2:1 and apparent formation constant values of 1.88 X 107and 2.96 X 108 M-2 were determined for the β-CD:pyrene in 54% v/v methanol-45 % v/v mobile phase mixtures containing 1 % v/v cyclopentanol and 1 % v/v tert-butyl alcohol, respectively. The implication of β-CD:pyrene:alcohol ternary complex formation and analytical chemistry applications of the concomitant effects are discussed.