AC-modulated voltfluorometric study of the transient adsorption of Rose Bengal dianions in the transfer across the 1,2-dichloroethane vertical bar water interface

The transfer of Rose Bengal dianion (RB2-), a fluorescent ion with asymmetr ic charge distribution, across the 1,2-dichloroethane (DCE)\ water (W) inte rface, has been studied using ac-modulated voltfluorometry, a method that c ombines ac voltammetry with fluorometry. The phase angle of the ac componen t of the fluorescence shifts to a value that cannot be explained by the the ory based on the simple combination of the heterogeneous ion transfer and m ass transfer. This anomaly strongly suggests that RB2- ions transiently ads orb at the interface in the course of the heterogeneous ion transfer. The r ate-determining step seems to be the adsorption-desorption of RB2- ions bet ween DCE and the interface. The apparent standard rate constant for ion tra nsfer across the interface is estimated to be 1.4 x 10(-2) cm s(-1). The ad sorption of RB2- appears to decelerate the rate of ion transfer across the interface.