Study Of Theory And Experiment Of Optical Fiber Measurment System For Pesticide Residues Based On Fluorescence Mechanism

With the development of agricultural science and technology, the pollution whichpesticides have brought about has done serious damage to the environment. Thoughpesticide residues are trace components, they can also do great harm to mankind's livesand health if people have contact with them for a long time. Therefore it becomesexceptional important to detect pesticide residues and their metabolites sensitively.There are some traditional analysis methods for pesticide residues, such as Thin LayerChromatography(TLC), Gas Chromatography(GC), High Efficiency LiquidChromatography(HPLC) and Biological Analysis et al. However, all of them have somedisadvantages including complicated sample pre-processing, consuming more reagentand more time etc. Thus it is impossible to realize fast and green detecting. Becauseoptical fiber fluorescence detecting technology has advantages of high sensitivity, littlesampling,fast detecting and simple operation, especially has advantages of on-line andcontinuous monitoring in the distance under any bad circumstances, it has been one of theresearch hotpots in environment monitoring. In this paper the technology of fluorescencespectrum detection and optical fiber sensing are applied to the study on theory andexperiment of direct detecting pesticide residues in vegetables. With the designedmeasurement system, pesticide residues can be detected fast and directly, as well as nopollution.Starting with the basic principle of fluorescence measurement, the feasibility offluorescence origin of some common pesticides, such as carbamate, benzoylurea andfungicide, is analyzed in theory, and the relationships between the characteristics ofnatural fluorescence and molecular structures are also researched, as well as theexcitation spectra and the fluorescence spectra of these pesticides and the fluorescencespectra of background solvent are studied by experiments, moreover, their best excitationwavelength and emission wavelength are studied and chosen.Based on the fluorescence characteristics of the pesticides, and combined with thetechnologies of optical fiber sensing, light dispersion of flat field grating and weak signaldetecting, a novel optical fiber measurement system for monitoring pesticide residues isdesigned. In this system, a pulsed xenon lamp is accepted as an excitation light sourceand several interference filters are equipped for selecting excitation light for differentpesticides, a high-efficiency sphere optical fiber probe is used to excite, collect andtransmit fluorescence, and a mini flat field spectrometer for fluorescence is designed torealize light dispersion in fine resolution, and a highly sensitive Charge Coupled Device(CCD) is used to detect weak fluorescence signals which are gathered and transformed bythe high speed data-gathering circuits whose control center is MCU and timinggenerator(ispLSI). Simultaneously the precise coupler is designed to realize coupling ofthe optical system efficiently, and the wavelength calibration of the system isimplemented by using a standard light source.Based on wavelet transform technology, digit filtering, smoothness and noise reductionof pesticides fluorescence spectra have been researched, and the mathematic model offluorescence quantitative analysis of pesticide residue has also been set up based onfluorescence spectrum analysis. By linearity calibration principle the concentrationmeasurement of a single component pesticide has been realized. Moreover, combinedwith derivative fluorescence spectra analysis, the concentration of each of thetwo-component pesticides is being mensurated without being separated beforehand.Experiments with standard pesticides and pesticide residues in farm water andvegetables have been made by the new fluorescence optical fiber measurement system forpesticide residues, their fluorescence spectra and the performance indexes of this system,such as the linearity, the minimum detecting limit, recovery and et al, are achievedsuccessfully. By comparing the experiment results of the new system with those of HPLCand GC, the performance of the new system is evaluated, and the rationality andpracticability of this system and the measurement method are validated.