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

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 mu g/25 ml for the CV system and 0-1.0 mu g/25 mi 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. (C) 1999 Elsevier Science B.V. All rights reserved.