| Pesticides can bring good harvest for fruits, vegetables and so on. Meanwhile, superfluous pesticides sprayed on the crops can make people’s health worse. With the development of people’s living standard, the quality of crops has been caused paying more attention on it. Especially the pesticide residues in the fruits and vegetables have been a focal point for the public. Therefore, considering the people’s health and environmental protection, it is the duty for the analysts to detect and precontrol the pesticide residues in the fruits and vegetables.There are many kinds of pesticides for crops, one of them organophosphorus pesticide is more toxic than others. At present, there are many methods reported for the determination of organophosphorus pesticides, such as chromatography, chromatography-MS, spectrum method, immunoassay, biosensor method and so on. Although, chromatography, chromatography-MS and spectrum method are sensitive and allow discrimination among different organophosphorus pesticides, they are expensive and require a long time not to satisfy the need of fast detection on the scene. Contrasting the above methods, biosensors based on enzyme inhibition technique provided a promising way to determine organophosphorus pestieides, which was both rapid and simple. With this method plenty of samples can be detected quickly and no expensive instrumenis. Though, the biosensors based on enzyme inhibition technique also have many disadvantages, such as low sensitivity, procedures trival, easy inactivation, instability and so on. In addition, the biosensors only can service for the single kinds of pesticides.Many kinds of pesticides have not the performance of electroactive. So, chemical derivatization is one of methods that can change the structures of them before the electrochemistry detecting. The aim of this work is mainly to explore the simple, sensitive and fast way to detect the no electroactive organophosphorus pestieides dichlofenthion, chlopyrifos and fungicide prochloraz and so on. In addition, the electrochemical dynamics parameters of ortho-phenyl phenol have also been studied and the electrochemistry method has been described for successfully used to detect its residue in orange rind. The specified studying content and results as followers:1. A ultrasensitive, simple and convenient electrochemical method was firstly developed for the determination of prochloraz and its metabolites as2,4,6-trichlorophenol (2,4,6-TCP) using nano-aperture medical stone. Compared with the undoped disposable electrode (UDE), nano-aperture medical stone doped disposable electrode (MSDDE) not only significantly enhances the oxidation peak current of2,4,6-TCP but also lowers the oxidation overpotential, suggesting that the nano-aperture MSDDE can remarkably improve the sensitivity of2,4,6-TCP. The experimental conditions such as pH values of buffer solution, the content of nano-aperture medical stone, accumulation potential and time were optimized for the determination of2,4,6-TCP. At optimal conditions, the oxidation peak current is proportional to the concentration of2,4,6-TCP over the range from6.0×10-9to8.0×10-5mol L-1. Finally, this novel method was successfully employed to detect prochloraz and its metabolites in orange rind with the detection limit of8.4×10-10mol L-1(0.3ng g-1) and the method was validated by gas chromatography.2. A novel photoelectric sensor for detection of organophosphorus pesticide (OP) dichlofenthion using nanometer titania coupled with screen printed electrode is presented. Nonelectroactive dichlofenthion can be indirectly determined through the nanometer titania photocatalytical degradation of dichlofenthion. The electrochemical characterization and anodic stripping voltammetric performance of dichlofenthion were evaluated using cyclic voltammetric (CV) and differential pulse anode stripping voltammetric (DPASV) analysis, respectively. DPASV was used to monitor the amount of dichlofenthion and provide a simple, fast, and facile quantitative method for dichlofenthion. Operational parameters, including the photocatalysis time, pH of buffer solution, deposition potential and accumulation time have been optimized. The stripping voltammetric response is linear over the0.02-0.1μmol L-1and0.2-1.0μmol L-1ranges with a detection limit of2.0nmol L-1. The assay result of dichlofenthion in green vegetables with the proposed method was in acceptable agreement with that of the gas chromatograph-mass spectrometer (GC-MS) method. The promising sensor opens a new opportunity for fast, portable and sensitive analysis of OPs in environmental samples.3. The electrochemical behavior of ortho-phenylphenol (OPP) at a disposable electrode (an improved wax-impregnated graphite electrode) in the presence of sodium dodecyl sulfate (SDS) was studied. The results demonstrated that the electrocatalytic oxidation process of OPP was accompanied with two-charge-two-proton transference. The electronic transmission coefficient (a) and diffusion coefficient (DR) for OPP were calculated to be0.8126and1.36×10-5cm2s-1, respectively. The electrochemical signal was apparently improved by SDS at the disposable electrode and the oxidative peaks current was proportional to the concentration of OPP over the range from1.0×10-9to4.0×10-6mol L-1with the detection limit of8.7×10-10mol L-1. This novel and highly sensitive method can be successfully applied to detect OPP in the orange rind sample.4. A dramatic visible light photoelectrochemical sensing platform for the detection of pesticide molecules at zero potential was firstly constructed using Poly(3-hexylthiophene)-functionalized TiO2nanoparticles. Poly(3-hexylthiophene)(P3HT) was synthesized via chemical oxidative polymerization with anhydrous FeCl3as oxidant,3-hexylthiophene as monomer, chloroform as solvent and the functional TiO2nanoparticles were facilely prepared by blending TiO2nanoparticles and P3HT in chloroform solution. The resulting photoelectrocatalysts were characterized by scanning electron microscopy, Raman spectroscopy, and X-ray diffractometer. Under visible light irradiation, P3HT generated transition from valence band to conduction band, delivering the excited electrons into the conduction band of TiO2, and then to the glass carbon electrode. Simultaneously, a positive charged hole (h+) of TiO2may form and migrate to the valence band of P3HT, which can react with H2O to generate·OH and then it converted chlopyrifos into chlopyrifos·that promoted the amplifying photocurrent response. Based on the proposed photoelectrochemical mechanism, a methodology for sensitive photoelectrochemical sensing for chlopyrifos at zero potential was thus developed. Under optimal conditions, the proposed photoelectrochemical method could detect chlopyrifos ranging from0.2to16μmol L-1with a detection limit of0.01μmol L-1at a signal-to-noise ratio of3. The photoelectrochemical sensor had an excellent specificity against the other pesticides and could be successfully applied to the detection of reduced chlopyrifos in green vegetables, showing a promising application in photoelectrochemical sensing. |
