A kinetic model for adsorption and transfer of ionic species at polarized liquid vertical bar liquid interfaces as studied by potential modulated fluorescence spectroscopy

Fundamental expressions for analyzing potential modulated fluorescence (PMF ) responses were derived within the framework of a phenomenological model f or adsorption and transfer of ionic species across polarized liquid/liquid interfaces. For small periodic perturbations of the Galvani potential diffe rence, PMF signals can be linearized and the contribution of each process c an be uncoupled it the frequency domain. The PMF response for kinetically c ontrolled adsorption is expressed as a semicircle in the complex plane in w hich the characteristic frequency of maximum imaginary component is proport ional to the adsorption and desorption rate constants. Considering that the potential dependence of adsorption exhibits opposite sign whether the proc ess take place from the aqueous or organic phase, the corresponding PMF res ponses appear in different quadrants of the complex plane. The present mode l delivers useful diagnostic criteria for analyzing the nature of the vario us processes contributing to the periodic fluorescence response. The adsorp tion dynamics of mesotetrakis(N-methyl-4-pyridyl)porphyrinato zinc(U) at th e water/1,2-dichloroethane interface were evaluated from the frequency depe ndent PMF responses. Studies performed at various Galvani potential differe nces clearly confirm that the adsorption can take place at two distinctive planes located at the aqueous and organic sides of the interface. Basic asp ects in connection to the nature of the adsorption planes are briefly discu ssed.