SPECTROPHOTOMETRIC DETERMINATION OF CATIONIC AND ANIONIC SURFACTANTS WITH ANIONIC DYES IN THE PRESENCE OF NONIONIC SURFACTANTS .1. A GENERAL ASPECT

The behavior of color development of anionic azo dyes, methyl orange and its analogues, was examined in aqueous media by changing the microenvironment of the dyes. The addition of alcohols, organic onium ions, anionic surfactants and nonionic surfactants brought about a decrease of the band at wavelengths near 480 nm and an increase of the band at wavelengths near 420 nm. Such a shift toward the shorter wavelengths in spectra was attributed to the change of the micro-environment around the dyes from a polar field to a less polar field; that is, the shift is caused by the change of the contribution of the following resonance forms, [GRAPHICS] On the basis of the color change phenomena, the spectrophotometric methods for the determination of organic onium ions and anionic surfactants were proposed.