Pesticides play a major role in ensuring the promotion of agriculture, forestry, and animal husbandry. At the same time, various residual impacts are increasingly attracting attention. At present, gas chromatography, mass spectrometry, and gas-liquid or liquid chromatography-mass spectrometry methods have been widely used or partially applied to pesticide residue detectors and confirmation tests. The accuracy of these methods is very high, but the pretreatment process of the sample is very cumbersome and can not adapt to the characteristics of the production and sales of vegetables in our country, and it is difficult to meet the rapid detection of pesticide residues in vegetables. Researching a rapid and simple pre-processing pesticide residue detection technology is a problem that needs to be solved urgently.
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Infrared spectroscopy technology is simple for sample preparation, has no pollution to the environment, and has fast analysis speed. It can simultaneously perform multi-component determination of pesticide residues. The related reports on the direct detection of residual chlorothalonil and other fungicides on the leaves of vegetables by the Ishizawa Group of Japan using the FTI R-ATR technology have attracted extensive attention. In this paper, the infrared absorption characteristics of pesticides in actual vegetables were studied by preparing pesticides and vegetable juice solutions. The standard reagents and vegetable juices were used as solvents to compare the infrared absorption of the commonly used high-residue pesticides trichlorfon and dichlorvos to achieve pesticides for vegetables. Residual direct rapid detection presents a possible method.
1 Experimental study
1.1 Instruments and Reagents Spectrlm GXI FTI R Fourier Transform Infrared Spectrometer (Perki nElmer); 45 ~ ATR Horizontal Attenuating Total Reflection Attachment (Pi ker Technologies). The ZnSe crystal measures the size of the surface: 40 mmX 10 mm. The reagents used were analytical chloroform and distilled water. Pesticides were made from 98% dichlorvos crude and 96% pure Trichlorfon (available from Tianjin Pesticide Co., Ltd.). Vegetable juice The inner leaves of fresh pollution-free Chinese cabbage sold by the market are squeezed by a juicer and gauze filters large particles of suspended solids.
1.2 Sample preparation (1) Take 1 g trichlorfon crude drug, add vegetable juice to 100 mL, and prepare a sample of trichlorfon vegetable juice with a concentration of 10 000 X 10 -6 mol·L-1.
(2) Take 1 g of trichlorfon crude drug, add distilled water to 100 mL, and prepare a sample solution of trichlorfon at a concentration of 10 000 X 10 -6 mol·L-1.
(3) Take 1 mL of dichlorvos crude oil and add vegetable juice to 100 mL. Suspension occurs. The suspension was shaken, allowed to stand for stratification, filtered, and a clear solution (the maximum concentration at room temperature) was taken as a sample of dichlorvos vegetable juice. From the density of dichlorvos at room temperature and its solubility in water, it is estimated that the concentration is approximately 2 000X10 -6 mol·L-1.
(4) Take 0.2 mL of dichlorvos crude oil, add chloroform to 100 mL, and prepare a sample of dichlorvos with a concentration of 2 000 X 10 -6 mol·L-1.
1.3 Experimental description Instrument parameter settings: spectrum acquisition range 2 000 !200 cm-1 with a resolution of 1 cm-1 and scan times of 16 times. The vegetable juice was filtered with filter paper, and the color-clear vegetable juice was not colored after the filter was filtered twice. The spectrum of the raw juice of vegetable juice and the absence of pigment after filtration by the filter paper was detected.
The vegetable juice solutions of trichlorfon and dichlorvos were prepared from unfiltered vegetable juice. Shake samples before injection. The spectra of the two pesticides in vegetable juice and standard reagent solvents were tested separately.
2 Results and Discussion
2.1 Characteristics of pesticides absorption site 
It is known from experiments that the two pesticide pure products absorb characteristically in the mid-infrared region. The peak position is shown in Table 1.
2. 2 Absorption of pigments in vegetables The spectral data of vegetable juices and filters without filter were measured. As shown in Figure 1. It can be seen that the two lines are almost coincident, with only slight differences around 3 300 cm-1. These slight differences between them can be seen as caused by instrument noise and injection errors. It is believed that in the mid-infrared range, almost no pigments are absorbed in vegetables. That is, when detecting the absorption of pesticides in vegetables, the interference of pigments on the absorption of pesticides in this range can be completely ignored. 
2.3 Absorption characteristics of pesticides under different types of solvents Absorbance data of the same concentration of [10 000 (10 -6 )] trichlorfon vegetable juice solution and water solution were respectively measured. 
as shown in picture 2. It can be seen that the characteristic absorption peak position of trichlorfon can be well reflected in both solvents. It is known from common knowledge that most of the leaf tissue of Chinese cabbage consists of water, so the absorption of pesticides in vegetables should be basically the same as in aqueous solution. The experimental results show that the position of the absorption peak of the pesticide trichlorphon in the two solvents is completely consistent; the absorbance in the vegetable juice is slightly lower than that in the distilled water solution, which may be caused by the absorption of unfiltered vegetable fibers and other impurities .
The absorbance data of approximately the same concentration (7 000 (10 -6 )) of dichlorvos vegetable juice solution and chloroform solution is shown in Fig.3. It can be seen from the experimental results that the position of the absorption peak of dichlorvos in the vegetable juice solvent can correspond to the characteristic absorption in the mid-infrared (see Table 1), while in the chloroform solvent, 1259. 2 cm-1 and 863. 4cm- The position of the peak at 1 has shifted. This is due to the strong polarity of the solvent chloroform, and its hydrogen bond affects the absorption frequency of the dichlorvos group, causing the position of the dichlorvos absorption peak to shift. In addition, the two absorbance curves do not coincide. In addition to the above reasons for the absorption of impurities in vegetables, the analysis of the light transmission ability of the two solvents shows that the absorption of vegetable juice in the 1 400 !800 cm-1 band (except for the vicinity of 1 215 cm-1) is much stronger than that of chloroform. (See Figure 4). Therefore, when the solvent background is subtracted, the absorbance of dichlorvos in vegetable juice is lower than that in chloroform. 
3 Conclusions In this paper, the mid-infrared attenuated total reflectance spectra of pesticides trichlorfon and dichlorvos in vegetable juice solvents were studied. The following conclusions were drawn: In the mid-infrared band, pigments in vegetables have no effect on the absorption of pesticides; pesticides in vegetable juice Medium absorption in distilled water is basically the same. The results of the study showed that the model can be used to simulate the absorption of pesticides in vegetables. This provides a possible method for the direct detection of pesticide residues in vegetables using infrared spectroscopy in the future.
