Study Of Fluorescence Properties And Analytical Methods Of Sudan Dyes

Sudan dyes are class of artificially synthetic azobenzene dyes mainly used as colorants. Recently, sudan dyes have been classified by the International Agency for Research on Cancer (IARC) as category 3 carcinogens due to their potential carcinogenicity. For this reason, sudan dyes are banned as food additives for human consumption. Therefore, a rapid, accurate and cost effective method of analysis for the determination of sudan dyes in foodstuff is extremely urgent for analysts both at home and abroad. Fluorescence spectrometry with its advantages of good selectivity, high sensitivity and low detection limits has wide applications in food safety and other related fields. So far there is no publication about the fluorescence characteristics of sudan dyes, therefore the research on fluorescence properties of sudan dyes and the development of analytical methods based on the characteristics have a great significance and valuable application. This thesis is mainly focusing on the investigation of the fluorescence properties of sudan dyes and the new rapid method for their detection. The thesis includes the following three chapters:In the first chapter, molecular structure, synthesis methods, physical and chemical properties, applications, and main sudan dyes contamination events happened recently at home and abroad were introduced. The harmfulness of sudan dyes and progress of their analytical methods were described explicitly. The theory, advantages and applications of synchronous fluorescence spectrometry were also introduced. The objectives of dissertation was put forward at the last part of this chapter.In the second chapter, we disclosured the fluorescence phenomenon of sudan dyes and studied their characterisics. The changes of sudan dyes' fluorescence properties in different concentrations of H₂SO₄ and KOH/ethanol solutions were investigated. The results show that the fluorescence peak positions of all the sudan dyes under investigation keep constant with the change in the concentration of sulfuric acid. Furthermore there was no change in the fluorescence intensity of sudanâ… and sudanâ…¡, in contrast with sudanâ…¢and sudanâ…£which exhibited a significant change in fluorescence intensity in different concentration H₂SO₄. In the KOH/ethanol solution, it was found that with the increase of the KOH concentration, the fluorescence intensity of molecular form of sudan dyes decreases, and the intensity of ion form increases gradually, but the ion form of Sudanâ…¢is non-fluorescent. From the isosbestic point in the fluorescence and absorption spectrum of sudan dyes, we can confirm that there is an equilibrium state between molecular and ion forms in acid/base solution. Molecular form exists mainly in the acidic solution while the ion form exists in the basic medium. When sudan dyes solution is heated in a water bath or exposed to infrared radiation, the intensity has a distinct increase and fluctuation. So we can make a primary conclusion that sudan dyes conduct trans and cis transformations when they are dealt with infrared radiation or heating.In the third chapter, a new method of constant-wavelength synchronous fluorescence spectrometry for simultaneous determination of sudanâ…¡and sudanâ…¢was developed. Sudanâ…¡and Sudanâ…¢exist in ion form at 0.2 g·L^-1 of KOH ethanol as solvent, and the fluorescence spectra overlap of the two dyes decreased. Combined with the synchronous fluorescence spectrometry, the spectral interference can be efficiently overcome. Only one single scan is needed for effective identification and quantitative determination of the two compounds simultaneously whenΔλ.=60 nm is chosen. The detection limits for sudanâ…¡and sudanâ…¢were 14 ng·mL^-1 and 11 ng·mL^-1, respectively. By using this method, sudanâ…¡and sudanâ…¢spiced in sausage samples were determined directly with good results. The recoveries of sudanâ…¡and sudanâ…¢in sausage were 83.8 %～109.5 % .