Correlation Between Inclusion Formation Constant and Distribution Coefficient in a Liquid–Liquid Extraction System Consisting of Hydrocarbon Solvents and Aqueous Dimethyl Sulfoxide Solutions of β-Cyclodextrin

Abstract

Carbazole was used as a fluorescence probe for the investigation of the correlation between the apparent formation constant (K _f ) for an inclusion complex of β-cyclodextrin (CD) and the distribution coefficient (K _d ) on liquid–liquid extraction. Single batch extractions of carbazole were performed at 25 ± 1 °C from three types of hydrocarbon solvents into an aqueous dimethyl sulfoxide (DMSO) phase containing CD or nothing. Both the K _f and K _d values for carbazole can be determined simultaneously under the same conditions on the basis of the extraction data. A plot of log K _f versus log K _d gives a straight line in both extraction systems of heptane and dodecane, with good correlations (0.9996 and 0.9992) and similar slopes (-0.675 and -0.672). The experimental results obtained from the cyclohexane–aqueous DMSO system suggest that the hydrocarbon used as the organic phase competes with carbazole for complexation with CD. The linear relationship is embodied in the form of an empirical equation, log K _fOB = -0.673 log K _d + log (K _fCR /K _fHY ), where K _fOB is the observed K _f value for a 1:1 carbazole–CD complex in the aqueous DMSO medium and K _fCR and K _fHY are the absolute K _f values in water for the carbazole– and hydrocarbon–CD complexes, respectively.