title: Estimating pH at the Air/Water Interface with a Confocal Fluorescence Microscope.
abstract: One way to determine the pH at the air/water interface with a confocal fluorescence microscope has been proposed. The relation between the pH at the air/water interface and that in a bulk solution has been formulated in connection with the adsorption equilibrium and the dissociation equilibrium of the dye adsorbed. Rhodamine B (RhB) is used as a surface-active fluorescent pH probe. The corrected fluorescence spectrum of RhB molecules at the air/water interface with the surface density of 1.0 nmol m(-2) level shows pH-dependent shifts representing an acid-base equilibrium. Two ways to determine the unknown acid-base equilibrium constant of RhB molecules at the air/water interface have been discussed. With surface-tension measurements, the adsorption properties, maximum surface density, and adsorption equilibrium constants were estimated for both cationic and zwitterionic forms of RhB molecules at the air/water interface.
authors.affiliation: Department of Molecular and Material Sciences, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University.
authors.forename: Haiya
authors.initials: H
authors.lastname: Yang
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Imanishi
authors.forename: Akira
authors.initials: A
authors.lastname: Harata