The Spectral Investigation Of Pyrethroid Pesticides By THz-TDS System

Terahertz time domain spectroscopy (THz-TDS) is a newly-developedfemtosecond laser pulse based THz technology. Being of high signal to noise ratioand insensitive to the thermal background and so on, this technology has been widelyused in various fields such as food, medicine, safety, chemistry, biological material.Pyrethroids pesticides are a type of pesticides which are of the broad-spectrum,highly efficient and low pollution, and they can be used for agricultural pestprotection and public heath territory. In this paper, we employed the terahertz timedomain spectroscopy to finish the qualitative and quantitative analysis on thepyrethroid pesticides.(1) The terahertz spectra of five kinds of pyrethroids pesticides were investigatedby terahertz time-domain spectroscopy, and the refractive index and absorptionspectra of the five kinds of pyrethroids pesticides from0.2to2.2THz were obtained.The result demonstrates that the experimental absorption spectra of all the fivepesticides had plenty of absorption peaks. The five pyrethroids pesticides were easilydiscriminated according to the absorption and refractive index spectra. We infer thesubstance which present apparent absorption peaks from0.2to1.5THz and nearby1.6,1.8,1.9THz may be pyrethroid pesticides for agricultural pest protection, and nosignificant law happened in pyrethroid pesticides for public heath territory due to thesignificant differences of structures. More experimental spectra of pyrethroidspesticides were needed for further validation.(2) For deeply understanding molecular configuration, The Gaussian03whichwas currently used in papers and CRYSTAL09were used for isolated-molecule andsolid-state simulation, respectively. The solid-state simulation predicted all theobserved experimental absorptions within0.2-2.2THz, which was better than theisolated-molecule for all the three density function theory. The IR active vibrationalmodes that comprise-cyhalothrin experimental spectrum was assigned and the result proved the absorption peaks presented in THz range mainly consist of internaland external motions.(3) The terahertz absorption spectra of different concentrations of deltamethrinpolyethylene mixtures and deltamethrin imidacloprid mixtures within0.2-1.6THzwere studied. We employed signal linear regression and partial least squares methodsto establish the relationship between absorption and deltamethrin content, and finishthe quantitative analysis on content of deltamethrin in the two kinds of mixtures. Thepartial least squares method provided better results than signal linear regressionmethod. From the partial least squares model, the detection limit of deltamethrin inthe deltamethrin polyethylene mixtures can be down to about2.0%, root mean squareerror was0.55%and maximum of the absolute error was0.8%. All the results werebetter than that of other paper. In the quantitative analysis on deltamethrinimidacloprid mixtures, root mean square error was1.45%, and absolute error can bedown to2.6%.This result proved the THz-TDS technique is quite potential for pesticidemolecular discrimination and content determination.