Feasibility study of the detection of chlorpyrifos residuals on apple skin based on infrared micro-imaging

Abstract. Infrared (IR) micro-imaging technology, also named chemical imaging, has potential applications in analytical technology. The IR micro-image provides not only the full spectrum information but also the component and structural information for each pixel point. Therefore, various groups of pesticides appear corresponding to the absorption peaks in the specific area of IR spectrum. In this study, the feasibility of using IR micro-imaging to detect chlopyrifos residuals on the surface of apple skin was explored. Different concentrations of chlorpyrifos solutions including 10,000, 1000, and 100  mg/L were sprayed on apple skin. Then IR micro-images were collected with a wavelength range of 4000 to 750  cm−1. The IR micro-image of chlorpyrifos pure powders was also collected for the contrasted analysis of characteristic absorption peaks. The results showed that there were seven, five, and four characteristic absorption peaks attributed to chlorpyrifos in the IR spectra of apple skin that was sprayed 10,000, 1000, and 100  mg/L chlorpyrifos solutions, respectively. With the decrease of chlorpyrifos solution concentration, the number of characteristic absorption peaks decreased. When the chlorpyrifos solution concentration was as low as 100  mg/L, the peak intensity could be still recognized. The second derivative spectra further validated the above conclusions. The detection limit of quantitative analysis was approximately 0.98  mg/L. The present study indicated that rapid detection of chlorpyrifos on the surface of an apple by IR micro-imaging technology was feasible. It provided useful foundation for the detection of fruits’ and vegetables’ pesticide residues by IR micro-imaging technology.