Study On The Fluorensecence Spectra Of Several Typical Organphosphorus Pesticides

Pesticides is widely used in crops for escaping from harmful pests and diseases because of its characteristics such as high efficient, convenient, wide adaptability, high economic efficiency and so on. It plays an important role in agricultural production. However, pesticides can not only kill harmful organisms, but also make damage to beneficial living things, the human body and the environment on which human being rely for existing. In recent years, as people's living standards improve,"food safety"arouses people's enormous interest increasingly, in which the pesticide residue is an issue that can not be ignored. With the development and application of the ultra-efficient pesticides and the increase of the sample, the sensitivity, specificity and rapidity of the pesticide residue analysis technology are claimed for a higher requirement. Then research on the rapid, simple and high sensitive pesticide residue analysis technology has an important significance.Based on the fluorescence analysis, the fluorescence of the four typical organophosphorus pesticides– methyl parathion, methamidophos, chlorpyrifos and dichlorvos was detected, the mechanism of the fluorescence was described theoretically, and different theoretical analysis methods for different organophosphorus were established.The spectral characteristic of methyl parathion standard solution induced by UV-light of 200 nm ~ 320 nm has been experimentally studied with the fluorescence spectra. The results show that there are four obvious fluorescence peaks generated. The peak position is located at 435 nm, 467 nm, 567 nm and 650 nm separately. The best excitation wavelength is 200 nm and 295 nm separately. The four fluorescence peaks are generated separately by the combined actions of the methyl parathion and the acetone. In methyl parathion molecule, there are the transition of n electrons in nitryl, the transition ofπelectronic structure formed by the oxygen atom and the benzene ring and the transition of n electrons in P=S group. In acetone molecule, there is the transition of n electrons in C=O group. In order to study the fluorescence spectra of Methyl Parathion and its characteristic, the theoretical calculation for the four fluorescent chromophore was made by using the fluorescent intensity additively principle. The calculated results are consistent with theoretical results. Using Gaussian software and the methods of quantum mechanics, the transition energy of methyl parathion were obtained and the transition energy of the linear structure fluorophore was estimated, and the experimental value has a little error to the theory value.The fluorescence spectrum of methamidophos EC market solution was detected by the spectral detection system in the UV excitation of 200 nm ~ 600 nm. The results show that a stronger fluorescence can be generated when pure solution of methamidophos 50% EC is excitated by UV light with a wavelength of 360nm and the peak position is located at 406 nm and 427 nm separately; a stronger fluorescence can be generated when dilute solution of methamidophos 50% EC is excitated by UV light with a wavelength of 280 nm, one peak position is located at 336nm and 427nm and the other is a range from 620~720nm. According to the principle of molecular spectroscopy, through analyzing, the fluorescence is generated by the transition of theπelectronic structure formed by the ? NH2 and P = O. The ? OH and ? H influence the fluorescence spectra and make change in the fluorescence peaks. Then the characteristic and the mechanism of the fluorescence spectra of methamidophos are explained.The spectral characteristic of chlorpyrifos standard solution induced by UV-light has been experimentally studied with the fluorescence spectra. The results show that there are three fluorescence peaks generated when chlorpyrifos standard solution is excitated by UV light with the wavelength of 200 nm~300 nm; when chlorpyrifos standard solution is excited by UV light with the wavelength of 200 nm~300 nm, the fluorescence spectrum is a wide peak. The three fluorescence peaks are generated separately by the transition of n electrons in"P=S", the transition of n electrons in heteroatom group "-O-" and the electronic transition of pyridyl. In addition, the fluorescence intensity of chlorpyrifos is analyzed by using quantum mechanics theory, and the results are consistent with the experimental results.Using the spectral detection system, the fluorescence spectra of the market dichlorvos 80% EC and dichlorvos standoard solution were detected. In the excitation of 250 nm ~ 400 nm, the fluorescence spectra of the market dichlorvos 80% EC and dichlorvos standoard solution are similar, which are two wide peaks of closed peak center and same trend, but the fluorescence intensity and the best excitation wavelength are different. Based on the high-resolution characteristics of derivative spectra, the second derivative of their fluorescence spectra in the best excitation wavelength was analyzed. It can be inferred that there are three fluorescent chromophores in dichlorvos molecular through the number and location of the minimum points in the second derivative spectra. The wide spectra peak is the result of the fluorescent chromophores'competition with each other, mutual constraints and combined effects.In this paper, the results of research expand application area of the fluorescence spectroscopy, and provide new ideas and new methods for food safety testing.