R. Okumura et al., ION-ASSOCIATION ADSORPTION OF WATER-SOLUBLE PORPHYRIN AT A LIQUID-LIQUID INTERFACE AND AN EXTERNAL ELECTRIC-FIELD EFFECT ON THE ADSORPTION, Analytical sciences, 12(3), 1996, pp. 393-397
By using total internal-reflection fluorescence (TIRE) spectroscopy it
was shown that an unprotonated form of water-soluble porphyrin (5,10,
15,20-tetraphenyl-21 H, 23 H-porphinetetrasulfonic acid, TPPS) is pref
erentially adsorbed over the diprotonated one by the toluene-water or
di(2-ethylhexyl)phthalate (DEHP)-water interface in the presence of a
cationic surfactant (cetyltrimethylammonium bromide, CTAB). The pH dep
endencies of the TIRF intensity were satisfactorily analyzed by a simp
le adsorption model, including the protonation equilibria in the bulk
aqueous phase and the adsorption equilibrium at the interface of TPPS.
Further, it was found that applying an electric field across the DEHP
-water interface significantly changed the ion-association adsorption
equilibria. This result was explained in terms of the electrophoresis
of TPPS in the interfacial region.