Determination Methods Of Malachite Green And Crystal Violet

Objective:Some potential carcinogens, such as malachite green (MG) and crystal violet (CV), are the significant organic contaminants, which are monitored for the safety of food or water. At present, the main detection methods of MG and CV are liquid chromatography and liquid chromatography tandem mass spectrometry. Resonance Rayleigh scattering (RRS) spectrum is a new sensitive quantitative analytical technique, which has been steadily developed recently, and has been applied widely to the study of life, environmental sciences and nanometer materials, etc. However, there are no reports discussing the determination of MG and CV by RRS. In this work, a sensitive, selective, simple and rapid method based on RRS was established for the determination of MG and CV.Methods:Triphenylmethane dyes MG and CV respectively react with some negative ions under suitable conditions to form a hydrophobic ion-associate. Then the ion-associate could self-assemble to form a nanoparticle, suspending in aqueous solution at suitable concentration and emitting intense RRS induced by excited ray. In this article, the effect of matrix on the intensity of RRS is analyzed theoretically based on the matrix negative absorption effect; the effect of pH is analyzed based on the conditional stability constant which is assayed by spectrophotometry; and MG and CV are analyzed qualitatively and quantitatively through detecting the intensity of RRS by the fluorescence spectrophotometer synchronously scanning.Results:In this article, the effects of matrix and pH on the intensity of RRS were analyzed based on the matrix negative absorption effect and conditional stability constant for the first time; novel methods were developed to analyze MG by RRS based on the forming of ion-associate of MG-I3- and MG-PMA (phosphomolybdate) respectively, and similarly a novel method was developed to analyze CV through the forming of ion-associate of CV-I₃^-. In the system of MG-I₃^-, the detection limit of the method is 3.6 ng/mL, the linearity range is 12～900 ng/mL, and the relative index r is 0.9997. In the system of MG-PMA, the detection limit of the method is 0.055μg/mL, the linearity range is 0.18～5.00μg/mL, and the relative index r is 0.9998. And In the system of CV-I₃^-, the detection limit of the method is 0.009μg/mL, the linearity range is 0.03～1.80μg/mL, and the relative index r is 0.9997.Conclusion:The sensitivity of the new method is similar to liquid chromatography and liquid chromatography tandem mass spectrometry, but RRS is simpler, faster and has no secondary pollution. So it is more suitable for the determination of MG and CV in the lower detection units.