# A Correction Method of Mixed Pesticide Content Prediction in Apple by Using Raman Spectra
## 3 Results and Discussion
### Pesticide Mixture Signal Analysis  
Surface-Enhanced Raman Scattering (SERS) signal acquisition was applied to standard solution of acetaminophen and deltamethrin pesticide and mixture of the two pesticides. There were literatures reported that main characteristic peaks of acetamiprid pesticide were located at 634, 1114 and 2164 cm\({}^{-1}\), and the characteristic peaks of deltamethrin were located at 574, 735 and 1380 cm\({}^{-1}\). Spectrum of characteristic peaks of pesticide mixture change with gradient concentration was shown in Figure 2. In the spectrogram, the characteristic peaks of the two pesticides were obvious and the intensity of the characteristic peaks changed with the concentration of pesticides consistently. Thus it was certain that peaks at 634, 1114, 2164 cm\({}^{-1}\) and 574, 735, 1380 cm\({}^{-1}\) were characteristic peaks of acetamiprid and deltamethrin pesticide. Overlapping peak didn't exist between acetamiprid and deltamethrin. In Raman spectral detection, the characteristic peak intensity reflects the concentration of samples. Thus quantitative analysis could be made from Raman spectral signal. With the decrease of pesticide content, the intensity values of deltamethrin and acetamiprid characteristic peaks reduce linearly. As shown in Figure 2.  
The location of the Raman vibration peak was only related to the vibration frequency of the chemical bond. Raman spectral peaks in different locations represented different chemical bonds [22]. According to common Raman spectral characteristic peak attribution map and comparison with other results analyze, it was possible to acquire the belonging of some characteristic peaks. Characteristic peaks of acetamiprid at 634, 1114 and 2167 cm\({}^{-1}\) belonged to C-CI retraction, ring vibration, and ring \"breathing\" respectively. Characteristic peaks of deltamethrin at 574, 735, 1380 cm\({}^{-1}\) were caused by C-Br retractable, symmetrical CBr\({}_{2}\) flexing and ring scaling. The analysis results were consistent with the study by [PERSON] [23]. And apple samples would cause no obvious Raman spectral peaks [24]. Figure 2: Spectrum of pesticide mixture characteristic peaks change with gradient concentration. As deltamethrin and acetamiprid were always be used in the same agricultural season, it was necessary to detect the mixture of the two pesticides. It could be seen clearly from Figure 3 that intensity of characteristic peaks of deltamethrin and acetamiprid pesticide mixture at 634, 1114 and 2167 cm\({}^{-1}\) was lower than the ones of single deltamethrin or acetamiprid pesticide solution, which affected the accuracy of detection result severely. It was clear that the intensity of characteristic peaks decreased when the other pesticide was added. Table 1 showed the detection results comparison of gradient concentration mixed pesticides concentration and real pesticides concentration. Through analyzing original spectra of the two pesticides, it could be found that decrement of the peak intensity was in a certain extent. And the extent depended on the concentration of the two pesticides, exposure time of laser and integration time of CCD camera, mainly the concentration of pesticides. Therefore it was necessary to find out the link between the decrement extent of characteristic peaks and concentration of pesticides, and then to get the actual detection result. By comparing a number of Raman spectra, it was clear to find that both characteristic peaks intensity value of single pesticide and pesticide mixture were steady in a range, which meant the multiple difference between single pesticide and pesticides mixture was certain. It was possible to find the ratio between characteristic peaks intensity value of single pesticide and the ones of pesticide mixture. Therefore the real peak intensity of one pesticide could be acquired through peak intensity of pesticides mixture and the ratios. The method of ratio would be realiable in Raman spectral detection of deltamethrin and acetamiprid mixture.