Abstract
2,4-Dichlorophenoxyacetic acid (2,4-D) is a common plant growth regulator, which can remain in food and, with long-term consumption, threaten human health. Therefore, it is necessary to propose an effective detection method. Terahertz time-domain spectroscopy technique (THz-TDS) has good advantages in the quantitative and qualitative analysis of most biomolecules due to its rich fingerprint characteristics. In this paper, density functional theory (DFT) was applied to geometry optimization and frequency vibration calculation of 2,4-D, and THz-TDS was used to quantitatively detect 2,4-D in Zizania latifolia. The results showed that there were three characteristic absorption peaks of 2,4-D at 1.36, 1.60, and 2.38 THz, respectively, and the theoretical spectra were in good consistency with experimental spectra, with slight discrepancies. Additionally, the absorption peak at 1.36 THz had the best absorption characteristics and was chosen as the main peak for 2,4-D quantitative analysis. It was demonstrated that the limits of detection (LOD) of 2,4-D in Zizania latifolia were found to be as low as 5%, the absorbance intensity at 1.36 THz showed a good linear relationship (R2 = 0.9854) with 2,4-D concentration from 5% to 30%, and the recovery was 93.29%–98.75%. Overall, this work enriched the fingerprint database of pesticide molecules on the basis of terahertz spectroscopy and could provide a technical support for the detection of 2,4-D in food by terahertz spectroscopy.
Highlights
College of Biosystems Engineering and Food Science, Zhejiang University, Hangzhou 310058, China; Key Laboratory of Spectroscopy Sensing, Ministry of Agriculture, Hangzhou 310058, China
It was showed that the limits of detection (LOD) of imidacloprid was lower than 8% and the relative error was less than 5% in predicting the weight ratio of imidacloprid in these two mixtures by the partial least squares (PLS) model
density functional theory (DFT) was applied to 2,4-D geometry optimization and vibration frequency calculation, and the generation mechanism of fingerprint peaks was explored
Summary
2,4-Dichlorophenoxyacetic acid (2,4-D) is a widely used plant growth regulator [1]. A small amount of it can promote crop growth and contribute to the improvement of fruit quality, and a large amount of it can help in weeding [2]. Trivedi et al [17] applied the UV–Vis spectrophotometer to detect the concentration of 2,4-D absorbed on mustard plant ash Still, these spectroscopy technologies had some shortcomings. Hua et al [26] applied THz-TDS technology to qualitatively and quantitatively detected four pesticides and three food powders in the frequency range of 0.5–1.6 THz. It was showed that the limits of detection (LOD) of imidacloprid was lower than 8% and the relative error was less than 5% in predicting the weight ratio of imidacloprid in these two mixtures by the partial least squares (PLS) model. Two antibiotics in three kinds of food were detected by the THz system, which indicated the feasibility of THz technology for detection of antibiotics in food These researches illustrated the existence of molecular terahertz fingerprint peaks and the potential of terahertz technology for quantitative detection of matters. It is believed that this work provides a theoretical and experimental basis for fingerprint peaks analysis of 2,4-D and a rapid method to detect 2,4-D in Zizania latifolia
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