Resonance Rayleigh scattering of chromium(VI)-iodide-basic triphenylmethane dye systems and their analytical application

Abstract

Resonance Rayleigh scattering (RRS) of chromium(VI)-iodide-basic triphenylmethane dye (BPTMD) systems and their analytical applications have been studied. In dilute phosphoric acid solution in the presence of excess I −, chromium(VI) oxidizes I − producing I 2, which binds I − to form I − 3 and I − 3 further reacts with a basic triphenylmethane dye such as crystal violet (CV), ethyl violet (EV), malachite green (MG), brilliant green (BG) and iodine green (IG) to form an ion-association complex. This results in the significant enhancement of RRS intensity and the appearance of new RRS spectra. The characteristics of RRS spectra of the ion-association complexes, the affecting factors and the optimum conditions of these reactions have been investigated. The intensity of RRS is directly proportional to the concentration of chromium(VI) in the range 0–1.5 μg/25 ml for the CV system and 0–1.0 μg/25 ml for the other systems. The methods have very high sensitivity and the detection limits for Cr(VI) are 0.065–5.6 ng ml −1 depending on the different reaction systems; the CV system is the most sensitive. A new method for the indirect determination of trace chromium(VI) on the basis of RRS has been advanced.