Abstract
Some chemical actions of nonionic surfactants have been studied which used as a prohibiting agent for the fading of iron(III)-thiocyanate color in the spectrophotometric determination of iron. Solubility of oxygen is not affected with the surfactant. The color is stable enough in the presence of the surfactant for two hours at 30°C, but it fades gradually when the solution is deaerated. Whereas the iron(II)-thiocyanate complex, which is usually not air-oxidized, changes into iron(III) complex in the surfactant solution, and red color appears. Therefore it is obvious that iron(III) thiocyanate is stabilized by dissolved oxygen activated with the surfactant. The reason why the surfactant remarkably enhances the color intensity has been assumed that the highly colored iron(III) complex coordinated with three or more thiocyanates is included in the micell of the surfactant just as the same complex is extracted with ether. Polyoxyethylene group of the surfactant might assist the extraction of the colored ion-pair by complexation with an alkali-metal ion. It would be noticed in the colorimetric use of this method that the large temperature dependence of the color reaction is promoted with the surfactant.
