Spectrophotometric Determination Of Nicotine And Melamine Based On Charge-transfer Reactions Coupled With Media Effects

In the introductory part in Chapter 1, some adverse events resulted from the toxic and harmful substances in certain foods and consumer goods were described. The significance of detection of nicotine and melamine and the research development in the analysis of these compounds were also outlined. Meanwhile, the charge transfer reaction and its analytical application were introduced. Then the research developments in the methodology of establishing second order data and in the chemometric algorithms for treating with the data were reviewed emphatically. In addition, the new methods proposed by this work for the determination of these compounds were also summarized.In Chapter 2,a new spectrophotometric method for the determination of nicotine based on a charge transfer reaction coupled with the sensitization effect of polyvinyl alcohol(PVA) was introduced. Nicotine could react with 2, 4-dinitrophenol (DNP) through a charge-transfer reaction to form a colored complex. In visible light range the absorption of the charge transfer complex could be remarkably enhanced by PVA. The maximum absorption wavelength of the complex is at 440 nm. The influence of acidity, chemical and manifold variables on the determination was studied. Under the optimized conditions, the linear range for the determination of nicotine was 2.0 ~ 60.0 mg/L with the detection limit of 0.85 mg/L. The proposed method was applied successfully for the determination of nicotine in tobacco samples with the recoveries of 98.3%～105.6%.In Chapter 3, a new spectrophotometric method for the determination of nicotine in mixtures by using second-order calibration without pre-separation has been proposed. The method is based on a charge-transfer reaction coupled with the effect of media components gradual change. Nicotine could react with DNP through a charge-transfer reaction to form a colored complex. The second-order data from the visible absorption spectra of the complex in a series of ethanol–water binary solvents with various water volume fractions could be expressed as the combination of two bilinear data matrices. With the bilinear model, the second-order spectra data of mixtures containing nicotine and other interferents could be analysed by using second-order calibration algorithms, and the determination of nicotine in the mixtures could be achieved. The algorithm used here were Rank Annihilation Factor Analysis (RAFA) and parallel factor analysis (PARAFAC), respectively. The method has been successfully used to determine nicotine in tobacco samples with satisfactory results.In Chapter 4, a new spectrophotometric method for the determination of melamine in foodstuffs by using second-order calibration was produced. The method is also based on a charge-transfer reaction coupled with the effect of media components gradual change. Melamine could react with DNP to form a colored charge-transfer complex. The second order data can be obtained from the spectra of melamine in a series of methanol- water binary solvents. Thus, the second order spectra data of mixtures containing melamine and other interferents could be also analysed using the second order calibration algorithms, and the determination of melamine in food samples could be achieved. The second order calibration algorithms were also based on the RAFA and PARAFAC, respectively. This method is simple, convenient and dependable. The method has been used to determine melamine in milk powder with satisfactory results.