A Study On The Identification Of Coffees By A Four-material Cataluminescence Spectral Array Sensor

In analytical chemistry, developing sensor technology for fast discrimination of complex mixtures with very similar components has always been sought after, but has been difficult to achieve. On the other hand, more attention has been paid on food quality and safety, which indicates that developing easy and efficient analytical methods in food analysis is urgently needed. Chemical sensors have been an important method in the analysis of complex mixtures. And cataluminescence(CTL)-based sensors play a very important role. CTL is the process by which organic components release faint light during oxidation reactions on the surface of catalytic materials. Analytes typically have different diffusion rates and physical or chemical absorptions. They also have different structures which produce differently structured intermediates and products. CTL provides a powerful tool for distinguishing between these different properties. From the CTL reaction system, one can easily gather a wealth of information such as signal strength, reaction time, wavelength, and spectral shape, to name a few. In addition, CTL sensors do not require a light source, which enables them to avoid scattered light interference and eliminates the influence of light source instability. They have the advantages of having simple equipment, high sensitivity, and fast analysis speed, which would be attractive to industry.The main contents of this thesis are as follows:(1) A novel CTL(cataluminescence) spectral array sensor was constructed using four types of materials(nano-MgO, nano-Y2O3, nano-Eu2O3, nano-Al2O3) within a closed system for the rapid identification of various types and brands of instant coffee. This sensor had the same volume with the single material CTL spectral array sensor, but more CTL information could get from it.(2) Each sample was tested in solution form and was subjected to CTL reactions with each of the four sensor materials. The intensities of light released in 15 wave bands were recorded for each sensor material, which were thus termed as a single material CTL spectral array. When the CTL reaction occured on four sensor materials, four groups of different spectral arrays could be obtained, 60 luminous intensities came into being, which were termed as four-material CTL spectral arrays.(3) In terms of data analysis methods, with software SPSS 20.0, linear discriminant analysis(LDA) as well as hierarchical cluster analysis(HCA) was performed on single material CTL spectral array of 7 instant black coffee products using chemometrics. Then, LDA and HCA were performed on four-material CTL spectral arrays of 7 instant black coffee products. The results showed that both the method LDA and HCA performed on single material CTL spectral arrays can classify 7 instant black coffee products, but the four-material CTL spectral arrays showed a much better classification.(4) LDA and HCA were performed on single material CTL spectral arrays of 14 instant coffee products with additives. Most coffee products could be classified, but not all of them. Then LDA was performed on two-material CTL spectral arrays, three-material CTL spectral arrays, four-material CTL spectral arrays of 14 instant coffee products with additives. The results showed that with the increase of spectral arrays, the diffierence among 14 instant coffee products with additives increased gradually. 14 coffee products were successfully classified. Then HCA was performed on four-material CTL spectral arrays of 14 instant coffee products with additives, 14 coffee products were identified correctly.(5) We gave a short disscuss on the mechanism. Different components in coffee released different light in CTL reaction, the CTL spectral array was the sum of all the light that the reactants released. The CTL spectral array would change while the experimental conditions, nano-materials change.Coffee products were successfully identified by four-material CTL spectral array sensor, which supplied a new method for the identification of complex mixtures with similar components. We can establish different multi-matierial CTL spectral sensor to identify different complex mixtures according to their properties.