Organochlorine pesticides are organic compounds containing organochlorine elements that are used to prevent and control plant diseases and pests. It is mainly divided into two categories: benzene based raw materials and cyclopentadiene based raw materials. The former includes the early and widely used insecticides DDT and hexachlorocyclohexane, as well as fungicides such as pentachloronitrobenzene, chlorothalonil, and Daofengning; The latter includes insecticides such as chlordane, heptachlor, and aldrin. In addition, camphene insecticides made from turpentine, toxaphene, and bornyl chloride made from terpenes also belong to organochlorine pesticides.

The method adopts supercritical CO2 extraction of organic chlorine pesticide residues in lettuce as a pretreatment method, with extraction pressure, extraction temperature, extraction flow rate, and extraction time as the evaluation factors. The recovery rate of eight types of organic chlorine pesticide residues is used as the evaluation index. The process conditions are optimized through orthogonal experiments, and the content of organic chlorine pesticide residues is determined by gas chromatography.

Experimental apparatus

　　gas chromatographFully compatible with Agilent 6890N gas chromatograph, it can be directly connected to Agilent 6890N detector and related detector control board, and can be connected to Agilent chromatography workstation and automatic sampler. The instrument's technical indicators, performance, and detector sensitivity are comparable to Agilent 6890N. *The design of the injection port solves injection discrimination, and the dual column compensation function not only solves the program drift caused by temperature rise, but also achieves lower detection limits; Two types of injection systems are available: packed column and capillary split/non split (with diaphragm cleaning function). Suitable for analysis and testing institutions such as food hygiene, medical equipment, electronic high-purity gas industry, fine chemicals, petroleum extraction and refining, petrochemicals, environmental monitoring, biotechnology, occupational health testing, quality supervision and inspection institutes.

　　sample preparationDilute the mixed standard solution with ethyl acetate to a standard solution of 100 ng/mL. To simulate a real environment, weigh 20 g of fresh lettuce leaves and chop them into small pieces. Use a syringe to extract 100 ng/mL

Inject 2 mL of standard solution into the lettuce leaves, place them in a refrigerator at 4 ℃ for 24 hours, and homogenize them into a paste using a homogenizer. Take 10 g of the above sample and weigh 10 g of diatomaceous earth (used to absorb water from lettuce, diatomaceous earth can absorb more than twice its own weight of water to avoid freezing and blocking the supercritical system, and diatomaceous earth is beneficial for sample dispersion). Mix the two and place them in an extraction kettle.

　　Chromatographic conditions：