Study On Bactericide Pesticide Detection In Agricultural Products By Terahertz Spectroscopy Technology

Terahertz (THz,1THz＝10¹²Hz) spectroscopy is a far-infrared analyticaltechnology with spectral bands locating between microwave and infrared ranges.Being of excellent transmission, non-destruction and high discrimination, thistechnology has been applied in various fields such as physics, chemistry,nondestructive detection, communication, biomedicine, public security. This paperdeals with the qualitative and quantitative study of nine bactericide pesticides,including the spectroscopic analyses of pure pesticides, fruits, mixtures of pesticideand fruits and of polyethylene and pesticides. In order to interpreting theexperimental spectra, the Gaussian03software is used to simulate the vibrationalmodes of pesticide molecule and the theory spectra explained some characteristicabsorption peaks of experimental absorption spectra. The absorption spectra ofmixtures of polyethylene and pesticide and of pesticide and fruits are quantitativelyanalyzed based on the spectra of their pure samples and the results were very well.The relationship is obtained between the concentration of pesticide solutions andtheir absorption spectra.The major content and innovations in this dissertation are listed as follows:（1） The uncertainty of THz-TDS system and the data processing model directlyaffects the experimental results. This paper theoretically analyzes and deduces theuncertainty sources influencing the precision in the experiment and processing data,for example, THz-TDS system uncertainty, the errors of samples, the transferfunction uncertainty. The results provide theoretical basis and reference to improvethe accuracy of experimental results.（2） Using the THz-TDS, the absorption spectra and refractive index spectra ofnine pure pesticide and three fruits are analyzed. The density functional theory （DFT）with the quantum chemical calculation software package Gaussian03using B3LYPtheory and the6-31G basis set is employed for optimization analysis, and the resultsof theoretical calculation agree with some absorptive peaks of the experimentalspectra well. The absorption spectra, refractive index and the characteristic peakswere set as the fingerprint of the pesticide, which can detect the different pesticides and fruits.（3） With THz-TDS, the absorbance spectra of one pesticide and polyethyleneand of two pesticides mixtures are quantitatively analyzed in0.2².2THz based ontheir pure fingerprint spectra, with further analyses of the influences of the pesticideand medium components on the mixtures spectra, and of the relationship between theabsorption spectra and the weight percentage of the pesticide components by themultiple linear regression.（4） The absorption spectra of quintozene methyl tertiary ether solutions with theconcentration in the level of several mg/ml are analyzed in0.5¹.05THz region, aswell as the relationship to the solution concentrations, and the first order derivativeof the absorption spectra is also quantitatively analyzed with their concentration.The results of the study show that pesticide and fruits are more sensitive toterahertz wave, and their absorption spectra, the refractive indexes and thecharacteristic absorption peaks are set as their fingerprint spectra. The agriculturalproducts and pesticide detection and identification by THz-TDS technology arefeasible.