Spectrophotometric determination of cationic micellar binding constant of ionised phenyl salicylate in the presence of inert salts

A spectrophotometric technique has been used to determine the cetyltrimethy lammonium bromide (CTABr) micellar binding constant (K-S) of ionised phenyl salicylate (PS.) in the presence of a constant amount of inert salt (MX = NaBr or C6H5COONa). The values of K-S at different [MX] follow an empirical relationship: K-S = K-S (0)/(1+ K-X/S[MX]) where the magnitude of the empi rical parameter K is the measure of the ability of X- to expel S- (= PS.) f rom the CTABr micellar pseudophase to the aqueous pseudophase. The value of K-X/S is nearly 13-fold larger for C6H5COO- than for Br-.