Study on Liquid-Liquid Interfacial Dynamics of Solvent Extraction Reaction by Total Reflection Laser-Induced Thermal Lens.

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The microscopic information about liquid-liquid interface is very important in analytical chemistry and separation science. A new interfacial thermal lens (TL) technique has been developed for the study on dynamics of solvent extraction.In this report, this technique applied to an ion-association reaction, the formation of Fe(II)-4,7-diphenyl-1,10-phenanthroline (DPP) complex at a benzene-acetate buffer interface. The thin TL effect of the complex adsorbed on the interface could directly present the complex formation by using a combination of total reflection excitation and pump (NdYAG pulse laser)-probe (red diode laser) alignment. At first, an amphiphilic molecule, 10-(1-pyrene) decanoic acid, expanded at a hexane-phosphate buffer solution interface was used to evaluate the specification of this technique. A response is linear to amounts of the expanded molecule and a minimum detectable amount is 1.0 x 10^<-10> mol corresponding about 1/100-monolayer. A time resolution is 0.1 second, which can monitor an initial stage of the complex formation.After the preparation of the interface TL signal increased gradually corresponding to the aging of the interface formation and the complex formation. The interfacial complex formation rate was proportional to the first order of Fe (II) concentration but did not vary with the DPP concentration. Two-step mechanism is proposed ; (1) the interface aging with an adsorption of DPP to the interface up to a constant amount, (2) the interfacial complex formation with Fe (II) from aqueous phase. The Langmuir adsorptions of the complex and the counter ion effects to the complex formation rate were also observed.