ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 20, Number 4
JKCSEZ 20(4)
August 20, 1976 

The absorption spectra and the dissociation constants of various sulfophthaleins have been measured in the presence of a cationic surfactant. In the presence of 2.0 × 10-3 M zephiramine and an ionic strength of 0.05 at 25±1℃ the absorption maxima of the basic forms are shifted to red by 6∼21 nm and their molar absorptivities are increased, while the absorption maxima of the yellow forms are shifted to blue by 4∼20 nm and their molar absorptivities are decreased. The decreases in pKa values are of the order of ranging -1.38∼0.37. The characteristic of the observed changes has been explained by the assumption that the dye molecule adsorbed on micellar surface forms a stable coplanar structure easily and then the conjugation in the dye molecule is elevated.