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Gas chromatographic analysis of organochlorine pesticides - Master's thesis - Dissertation
In the modern agricultural industry, the use of pesticides has become widespread, with a diverse range of chemicals applied across large geographical areas. As economies develop, the demand for these substances increases, often leading to overuse. While pesticides can significantly boost crop yields and support food production, they also pose serious environmental and health risks. Pesticide contamination can affect soil quality, pollute water sources, and leave harmful residues in food products, which may ultimately impact human health.
The issue of pesticide residues is a critical concern in today's environmental and public health discussions. Due to the high frequency and volume of pesticide applications, it's common for crops—especially fruits—to carry residual chemicals. A recent study conducted by researchers in the U.S. and the U.K. revealed that 73% of tested food crops showed no detectable pesticide residues, but vegetables and fruits were more affected. Additionally, after harvest, many fruits are stored for extended periods before reaching consumers, making the use of preservatives like fungicides almost unavoidable. As a result, both the outer skin and inner pulp of these fruits may contain pesticide residues.
One of the most concerning types of pesticide residue is organochlorine pesticides. These compounds, such as BHC (Benzene Hexachloride) and DDT (Dichlorodiphenyltrichloroethane), have been widely used in agriculture but are now banned or restricted due to their long-term environmental persistence and toxic effects. Despite China banning the production of BHC and DDT in 1983, these substances remain problematic because they degrade very slowly. For example, dicofol is still used on fruit trees and cotton, and its metabolite, DDE, is structurally similar to DDT and exhibits comparable toxicity. This means that even today, crops may still contain traces of these harmful chemicals.
To monitor and control these residues, various analytical methods are available, but gas chromatography stands out for its accuracy, sensitivity, and efficiency. The GC-7800 gas chromatograph, produced by Beijing Purui Analytical Instrument Co., Ltd., is one such device widely used for detecting pesticide residues. According to the Chinese national standard GB/T 17332-1998, this instrument has proven effective in analyzing organochlorine pesticide levels in tea samples, delivering reliable and consistent results.
In the experimental setup, the GC-7800 was paired with an OV-1701 or SE-54 column (30m × 0.32mm × 0.5μm) from Dalian Zhonghuida Scientific Instrument Co., Ltd. The experiment utilized an Electron Capture Detector (ECD) for high sensitivity detection. The column temperature was set at 200°C, while the injection and detector temperatures were maintained at 220°C. A high-purity nitrogen carrier gas was used at a flow rate of 8 mL/min, with a tail gas flow of 16 mL/min. A 1 μL injection volume ensured precise and reproducible analysis. This method provides a robust approach for identifying and quantifying organochlorine pesticide residues in agricultural products, supporting efforts to ensure food safety and environmental protection.