Differential Kinetic Spectrophotometric Determination Of Some Residual Substances In Food And Environment With The Aids Of Chemometrics

The research mainly aims at a growing concern for the food and environment aspects of the complex multi-component systems for rapid quantitative determination. Meanwhile, an overview of the application of chemometric approaches to determination some residual substances in food and environment samples in recent years was studied. The chemometrics methods were used for the analysis of the spectra and the kinetic data, which obtained from the experimental, then discussed the principles of kinetic method and its practical application, and explored the feasibility of using chemometrics in the complex system to achieve simultaneous determination of multi-component material.This thesis is composed of five chapters.Chapter 1In this chapter, the application of chemometric approaches to kinetic analysis for the aspects of food and environmental was reviewed. Multivariate calibration approaches based on factor analysis and artificial neural networks approaches are summarized and discussed. In addition, the prospects of chemometrics in kinetic analysis were also given.Chapter 2A method for the simultaneous enzymatic kinetic determination of the pesticides, oxamyl, aldicarb and aminocarb in fruit, vegetable and water samples, has been developed. It was based on enzymatic reaction kinetics and spectrophotometric measurements, and results were interpreted with the aid of chemometrics. The analytical method relies on the inhibitory effect of the pesticides on acetylcholinesterase(AChE), and the use of 5,5'-dithiobis (2-nitrobenzoic) acid (DTNB) as a chromogenic reagent for the thiocholine iodide (TChI) released from the acetylthiocholine iodide (ATChI) substrate. The complex rate equation for the formation of the chromogenic product, P, was solved under certain experimental conditions, which enabled the absorbance (Ap, atλmax=412nm) from the mixtures of the three pesticide inhibitors to be directly related to their concentrations. The detection limits of the enzymatic kinetic spectrophotometric procedures for the determination of the oxamyl, aldicarb and aminocarb were 0.81,2.13 and 1.25ng mL-1, respectively. Calibration models for chemometrics methods, such as principal component regression (PCR), partial least squares(PLS) and radial basis function-artificial neural network (RBF-ANN), were constructed and verified with synthetic samples of the mixtures of the three pesticides. The prediction performance of the calibration models constructed on the basis of these methods was compared. It was shown that satisfactory quantitative results can be obtained with the use of RBF-ANN model with relative prediction error (RPET) of 7.59% and an average recovery of 99%. The RBF-ANN method was successfully applied to determine the contents of these three compounds in fruit, vegetable and water samples with satisfactory results.Chapter 3A new kinetic spectrophotometric method for simultaneous determination of chlortetracycline, tetracycline and oxytetracycline in muscle samples has been developed. The method is based upon the investigation of the kinetic reaction of the drugs with alkaline potassium permanganate at 40℃. The increasing absorbance of the colored manganate at 526nm and decreasing absorbance of potassium permanganate at 608 nm were measured after the addition of the drugs. The plot of absorbance versus concentration was rectilinear over the range of 0.05-0.75μg mL-1 for chlortetracycline and tetracycline, and 0.02-0.34μg mL-1 for oxytetracycline, with limit of detection of 0.013,0.015 and 0.011μg mL-1, respectively. The experimental conditions affecting the development and stability of the color products were carefully investigated and optimized. The proposed method was successfully applied to the determination of the tetracyclines in feed and muscle samples, and the results showed excellent agreement with that of HPLC method.Chapter 4A selective and simple kinetic spectrophotometric has been developed for the simultaneous determination of three misusedβ2-agonists, clenbuterol, ractopamine and salbutamol in muscle and pig liver samples. The procedure was based upon the difference in the rate of oxidation of these compounds with yellow ammonium cerous sulfate in appropriate acidic medium and formation of colorless cerous sulfate. Three species instantly oxidize, giving rise to compounds which present maximum values of absorbance close to 312nm. Under the optimized experimental conditions, the chemometrics multivariate calibration methods, such as partial least squares(PLS), principal components regression(PCR), radial basis function-artificial neural network (RBF-ANN) were applied to the resolution of the kinetic curves. Eachβ2-agonists could be determinated in the linear range of 0.1-1.9μg mL-1,0.1-1.6μg mL-1 and 0.1-1.6μg mL-1 for clenbuterol, ractopamine and salbutamol, respectively. The limits of detections are 0.024,0.068 and 0.027μg mL-1 for clenbuterol, ractopamine and salbutamol, respectively. The proposed method was compared to other methods for determination ofβ2-agonists, and it was proved to be adequately reliable and was successfully applied to simultaneous determination of clenbuterol, ractopamine and salbutamol in feed, muscle and pork liver samples, obtaining the satisfactory results based on recovery studies(93.2-102.8%).Chapter 5In the last part, a sensitive inhibitory fluorimetric kinetic method for the simultaneous quantitative determination of diethion and chlorpyrifos was proposed. It was shown that Fenton reagent oxidized rhodamine B in acid medium which enabled the fluorescence quenching of the latter. The presence of trace diethion and chlorpyrifos clearly inhibited the reaction, and they were different in the inhibitory effect of the reaction. Upon addition of EDTA, a good linear relationship between the inhibitory effect and the concentration of diethion and chlorpyrifos were observed, together with improved stabilization and sensitivity. Factors affecting the determination of diethion and chlorpyrifos were investigated systematically by central composite design. The analytical curves give a linear range of 0.2-3.8 and 0.05-0.95ng mL-1 for diethion and chlorpyrifos, respectively. The kinetic data obtained were processed by chemometrics methods, such as partial least squares, principal component regression(PCR), and radial basis function-artificial neural network(RBF-ANN). The results show that PLS model has advantages for the prediction of the analytes, and it gave the lower prediction errors than other chemometrics methods. Following the validation of the proposed method, it was applied for the determination of diethion and chlorpyrifos in water samples; and the standard addition method yielded satisfactory recoveries.