Quantitative Determination Of Some Hazardous Substances In Foods And Environment By Electroanalytical Methods With The Aid Of Chemometrics

This thesis contains five parts, and the research mainly focus on the determination of some hazardous substances in foods and environment by use of electrochemical voltammetry. In complicated matrixs, there may exist a variety of similar substances. Because of their voltammetric spectra overlapped, some chemometric methods were used to resolve the overlapped voltammograms. The experiments results show the powerful resolution capability of chemometrics.Part one:Firstly, a brief introduction to this thesis topics and to the methods used in this thesis was described. Secondly, a review of the developed electrochemical detection methods in the last five years was given, such as the direct potential method, potentiometric titration, polarography and voltammetry. Finally, a brief application of the modified electrodes and chemometrics in electrochemistry was presented.Part two:A simple, rapid, low-cost and reliable method for the simultaneous determination of three antibiotic drugs by differential pulse stripping voltammetry (DPSV) in Britton-Robinson buffer (pH=7.96) is presented. The optimal conditions were, the deposition time of80s, the deposition potential of-1250mV, and the scan rate of25mV s-1. Under optimal conditions, the linear concentration ranges were0.010-0.080μg mL-1for all these three antibiotic drugs, and the detection limits were2.38,3.20and1.60ng mL-1for Levofloxacin, Gatifloxacin and Lomefloxacin, respectively. For the voltammograms of these three drugs are overlapped seriously and it is difficult to determine each of them from a response of drug mixture, chemometrics methods, such as classical least squares (CLS), partial least squares (PLS), principle component regression (PCR) and radial basis function-artificial neural networks (RBF-ANN), were applied to quantitatively resolve the overlapping signals in this work. It was found that the PCR gave the best results with total relative prediction error (RPET) of7.71%. The obtained results of antibiotic drugs with the proposed method were verified with the high-performance liquid chromatography method (HPLC). Following the validation of the proposed method, it was applied to the determination of the antibiotic drugs in several commercial food samples, milk, egg and honey samples, with spiked method the recovery.results were satisfactory.Part three:A differential pulse stripping voltammetric (DPSV) method for the determination of three colorants, sunset yellow, amaranth and tartrazine, was developed. The method is based on the adsorptive accumulation of the colorants on the glassy carbon electrode, followed by the oxidation of the adsorptive species by the voltammetry. It was found that the optimal condition of CTAB (cetyltrimethyl ammonium bromide) was40.0×10-6mol/L used as the for the experiment. The linear concentration ranges were4.0-40.0,5.0-60.0and2.5-35.0nmol/L, for sunset yellow, amaranth and tartrazine, respectively, and their corresponding detection limits were1.54,2.38and1.10nmol/L. because the voltammograms of these colorants are seriously overlapped and it is difficult to determine them individually from the voltammetric signals of the mixtures, herein, chemometrics methods, such as partial least squares (PLS), principle component regression (PCR) and their first-order derivative methods (DPLS and DPCR), were applied to quantitatively resolve the overlapping signals in this work. It was found that the DPLS gave the best results with total relative prediction error (RPET) of6.18%. The proposed method was applied to the determination of the three colorants in several commercial food samples, soft drink, ice cream and candy samples, with spiked method the recovery.results were satisfactory.Part four:In this paper, we report a highly rapid, accurate and sensitive voltammetric method for the determination of bisphenol A(BPA) at a nano-titanium dioxide and graphene oxide (nano-TiO2/Graphene) hybrid materials modified glassy carbon electrode. Due to the excellent catalytic activity, enhanced electrical conductivity and high surface area of the modified electrode, the electrochemical behavior of bisphenol A has been investigated using differential pulse stripping voltammetry, the oxidation current of bisphenol A increased significantly. The linear range for determination of BPA was obtained in the range of10-490nmol/Lwith the detection limit of2.83nmol/L. Furthermore, the fabricated sensor was applied to determinate BPA in the plastic film, yoghurt box, mineral water bottle and food packing samples, with spiked method and yielded satisfactory recovery values between95.7%and101.4%.Part five:Glassy carbon electrode modified with electrodeposited Acid Chrome Blue K (ACBK) was used to determine the trace amounts of aminophenol isomers, p-Aminophenol(PAP), o-Aminophenol(OAP) and m-Aminophenol(MAP). Compared with bare GCE, the modified electrode presented an excellent response of the three aminophenols. As the electrochemical approach shows a very high overlaping degree for the three aminophenol voltammograms, the first order derivative voltammetric method was applied to quantitatively resolve the overlapping signals in this work. It was found that three well-separate peaks were achieved. Under the optimum conditions, the response peak currents were linear relationship with the PAP, OAP and MAP concentrations in the range of0.25-5.00,0.25-4.50and0.25-3.75μmol/L, respectively, and their corresponding detection limits were0.074,0.064and0.071μmol/L. The proposed method was successfully applied to the determination of aminophenol isomers in water samples with spiked method the recovery.results were satisfactory.