AC-Modulated Voltfluorometric Study of the Transient Adsorption of Rose Bengal Dianions in the Transfer across the 1,2-Dichloroethane|Water Interface

The transfer of Rose Bengal dianion (RB 2- ), a fluorescent ion with asymmetric charge distribution, across the 1,2-dichloroethane (DCE)|water (W) interface, has been studied using ac-modulated voltfluorometry, a method that combines ac voltammetry with fluorometry. The phase angle of the ac component of the fluorescence shifts to a value that cannot be explained by the theory based on the simple combination of the heterogeneous ion transfer and mass transfer. This anomaly strongly suggests that RB 2- ions transiently adsorb at the interface in the course of the heterogeneous ion transfer. The rate-determining step seems to be the adsorption−desorption of RB 2- ions between DCE and the interface. The apparent standard rate constant for ion transfer across the interface is estimated to be 1.4 × 10 -2 cm s -1 . The adsorption of RB 2- appears to decelerate the rate of ion transfer across the interface.