Tungstate ion resonance Rayleigh scattering method for determination of basic triphenylmethane dyes

In a pH 4.2-6.0 HAc-NaAc buffer medium,the resonance Rayleigh scattering intensities of separate basic triphenylmethane dyes,such as methyl violet (MV),ethyl violet (EV),crystal violet (CV),methyl green (MeG),iodine green (IG),malachite green (MG),light green (LG),and tungstate ion solution,are very weak,but when these cationic dyes react with the tungstate ion (WO 42-) to form ion-association complexes,their RRS are enhanced sharply and new RRS spectra appear.The reaction products of methyl violet,ethyl violet,and crystal violet with WO 42-have similar spectral characteristics and there are two strong RRS peaks at 330 nm and 560 nm.The reaction products of methyl green,iodine green,malachite green,light green with WO 42-have similar spectral characteristics and there are three RRS peaks at about 335 nm,450 nm and 580 nm.The sensitivities of seven kinds of reaction products show a sequence of malachite green>light green>crystal violet>ethyl violet>methyl green>iodine green>methyl violet.The linear ranges and detection limits of the above seven systems are 0.06-2.78 μg mL-1 and 18.1 ng mL-1 (MG),0.08-4.83 μg mL-1 and 22.6 ng mL-1 (BG),0.10-4.90 μg mL-1 and 31.4 ng mL-1 (CV),0.14-2.95 μg mL-1 and 40.5 ng mL-1 (EV),0.17-3.70 μg mL-1 and 50.2 ng mL-1 (MeG),0.22-5.70 μg mL-1 and 67.1 ng mL-1 (IG),and 0.25-7.30 μg mL-1 and 76.3 ng mL-1 (MV).A sensitive,simple and fast RRS method for the determination of basic triphenylmethane dyes using the tungstate ion as the probe has been developed.The method is applicable to the determination of malachite green residues in fish flesh.