Study On Recognition Technology Of Pesticides Containing Cyano Group Based On Raman Silent Region

The pesticides can prevent crop diseases and improve crop yield.However,pesticide residues seriously affect food safety and threaten human health.Gas chromatography is commonly used in pesticide residues detection technology.More than 500 pesticides can be detected simultaneously,but it can not be detected on site.The demand for pesticides detection comes from the front end of the supply chain of edible agricultural products,with a large turnover and most of them have no fixed places.Therefore,it is urgent to develop a rapid,simple and field application detection technology.Surface enhanced Raman spectroscopy(SERS)is widely used in the detection field because of its advantages of accurate identification,fast speed and miniaturization of equipment.However,Raman spectroscopy is easily interfered by complex matrix from samples.The characteristic peaks of target molecules overlap with the Raman peaks of matrix,which makes it difficult to detect the target qualitatively and quantitatively.Some pesticides can be classified because of their chemical structure containing cyano(C?N)group,including herbicides,insecticides,fungicides and so on.The Raman signal of cyano(C?N)group is located in the Raman silent region(1800-2800 cm^-1),and the background interference of the matrix can be avoided.Based on the phenomenon of photolysis of pesticides under UV irradiation and the stable signal in the Raman silent region,a SERS detection method for cymoxanil and azoxystrobin was established.1.In order to detect the signal of cymoxanil in the Raman silent region,the effects of solvent,light source,illumination time and other conditions on the SERS detection were investigated.The results showed that methanol was used as solvent and be irradiated under302 nm UV light source for 30 min,cymoxanil in plastic centrifuge tube could be detected by Raman spectroscopy at room temperature.Au NPs with particle size of 40-80 nm was used as the SERS substrate.The limit of detection was 0.5 mg/L,and in the concentration range of1.0-50.0 mg/L,there was a good linear relationship between the peak intensity at 2130 cm-1and the concentration,R=0.9953.Cucumbers and grapes were chosen as the real samples,the recoveries were in the range of 88.23%-106.58%,which met the detection requirements.The rusults of SERS and HPLC were consistent.In addition,the photoproducts of cymoxanil were identified by ultra performance liquid chromatography quadrupole time-of-flight mass spectrometry(UPLC-TOF-MS).Combined with the identification of the Raman peaks in the SERS spectra of the photolysis solution,it was confirmed that the peak at the Raman silent region came from the shedding of C?N during the photolysis process.2.In order to detect the signal of azoxystrobin in the Raman silent region,the effects of solvent,light source,illumination time and accelerator on the signal were investigated.The results showed that when methanol-water(1:1)was used as solvent and being irradiated under302 nm light source for 20 min,plastic centrifuge tube was used as illumination container,0.5M KI was used as accelerator,and the amount of sample was 5?L(20?l mixture of 40-80nm colloidal gold and 10?l solution to be determined),the SERS detection of azoxystrobin could be realized.The limit of detection was as low as 0.5 mg/L,the linear concentration range was 0.5-25 mg/L,R=0.9880;grape was used as the real sample for standard addition experiment,and the recovery was 82.10%-108.14%,indicating that the SERS method is feasible in the actual detection.3.The signals of pesticides containing cyano group in the Raman silent region were studied.The SERS spectra of four kinds of pesticides containing cyano group and four kinds of pesticides without cyano group before and after UV irradiation were collected.The results showed that there was no Raman signal in the silent region of pesticides without cyano group before and after UV irradiation,while pesticides containing cyano group could be detected by SERS directly,and there was a signal in the Raman silent region.After mixing different types of pesticides,the SERS spectra before and after UV irradiation were collected respectively.According to the change of SERS spectra in the Raman silent region,whether there are pesticides containing cyano group and their categories can be judged.