Study On Solid Phase Extraction Of Organophosphorous Pesticides By Modified Magnesium Aluminum Layered Metal Hydroxide

Agriculture is the lifeblood of national economy in China.In order to make the output of agriculture products meet the demand of the people's living standard,the pesticides have to be used to drive away pests and remove weeds.The widespread application of pesticides has successfully suppressed the outbreak of many dangerous diseases and insect pests and increased the yield of crops.However,the pesticide residues in the environment also pose a threat to human health,so we must monitor pesticide residues in the environment.As the content of pesticide residues in the environment is very low,the study of separating and enriching method is conducive to accurately and rapidly monitoring pesticide pollution in the environment.In this study,we prepared sodium dodecyl sulfate intercalation modified magnesium aluminum layered metal hydroxide?Mg-Al-SDS-LDH?and magnesium aluminum iron layered metal hydroxide?Mg-Al-Fe-LDH?,used the two composite materials as solid phase extractants,established two analytical methods for the determination of dichlorvos,dimethoate,chlorpyrifos and isocarbophos in water by solid phase extraction-gas chromatography-mass spectrometry.The main research works and results are as follows:?1?The method of Mg-Al-SDS-LDH solid phase extraction-gas chromatography-mass spectrometry for the determination of dichlorvos,dimethoate,chlorpyrifos and isocarbophos was established.The Mg-Al-SDS-LDH was prepared by roasting recovery method.When the molar ratio of Mg²⁺:Al³⁺was 3:1,the aging temperature was 80°C,and the aging time was 14 h,the best magnesium-aluminum layered hydroxide?Mg-Al-LDH?was obtained.After roasting at 400°C for 2 h,weighed 2 g of the material,the amount of SDS added was 15%of the material,and reacted at 120°C for 1 h to obtain Mg-Al-SDS-LDH.The saturated adsorption capacity of Mg-Al-SDS-LDH for chlorpyrifos and isocarbophos reach 5.7 mg/g and4.1 mg/g.Scanning electron microscope?SEM?,x-ray diffraction?XRD?,fourier transform infrared spectrometer?FT-IR?,thermogravimetric?TG-DTG?and specific surface area?BET?characterization show:the appearance of Mg-Al-SDS-LDH is a sheet with rough surface,it has an interlayer structure of magnesium aluminum layered hydroxide with layer spacing of 0.791 nm.The stretching vibration peaks of C-H and S=O of the SDS appear in the infrared spectrum.There are two main stages of weightlessness within 600°C.Specific surface area is 14.7 m²/g,and pore size is mainly concentrated in 3-12 nm,which belongs to layered metal mesoporous material.When the dosage of Mg-Al-SDS-LDH is 2 g,the extraction time is 8 min,dichloromethane is used as the eluent,the dosage of the eluent is 4.5 m L,and the elution time is 1 min,the best extraction efficiency is achieved for 100 m L 0.2?g/m L of chlorpyrifos and isocarbophos,the extraction rate are 93.5%and 90.1%,respectively.Under the optimized extraction and determination conditions,the linear range of gas chromatography-mass spectrometry determination for dichlorvos,dimethoate,chlorpyrifos and isocarbophos is 0.005?10 ng/m L,the correlation coefficients are all greater than 0.99,the relative standard deviation is 1.7%?3.0%,the detection limit is 0.0005?0.01 ng/m L,and the enrichment multiples are 17,12,42 and38 times,respectively.?2?The method of Mg-Al-Fe-LDH solid phase extraction-gas chromatography-mass spectrometry for the determination of dichlorvos,dimethoate,chlorpyrifos and isocarbophos was established.When the molar ratio of Al³⁺:Fe³⁺was0.8:0.2,the aging temperature was 80°C,and the aging time was 14 h,Mg-Al-Fe-LDH was prepared by co-precipitation method.SEM,XRD,FT-IR,TG-DTG,BET and x-ray photoelectron spectroscopy?XPS?characterization results show:the appearance of Mg-Al-Fe-LDH is a sheet with uneven size,it has an layered structure,and the layer spacing is 0.779 nm.Fe-O stretching vibration peak appears in the infrared spectrum.There are two stages of weightlessness in the TG-DTG spectrum within 600°C.Specific surface area is 75.7 m²/g,and pore size is mainly concentrated in 3-10 nm,which belongs to layered metal mesoporous material.The saturation adsorption capacities of Mg-Al-Fe-LDH for clopyriphos and isocarbophos are 2.0 mg/g and 1.5 mg/g,respectively.When the dosage of Mg-Al-Fe-LDH is 2 g,extract 100 m L 0.2?g/m L of chlorpyrifos and isocarbophos for 12 min,dichloromethane is used as the eluent,the eluent dosage is 4.5 m L,and the elution time is 1 min,the extraction rates of the two pesticides are 75.4%and 71.2%,respectively.Under the optimized extraction and determination conditions,the linear range of gas chromatography-mass spectrometry determination for dichlorvos,dimethoate,chlorpyrifos and isocarbophos is 0.01?10 ng/m L,the correlation coefficients are all greater than 0.99,and the relative standard deviation is 1.1?3.6%,the detection limit is 0.001?0.03 ng/m L,and the enrichment multiples are 12,9,33,and 28 times,respectively.?3?The two methods are applied to paddy field water in Nanchong,Sichuan,which can effectively detect dichlorvos,chlorpyrifos and isocarbophos.The results indicate that the content of organophosphorus pesticides detected in paddy field water are within the allowable value[GB 3838-2002].The recovery rates of the four samples of paddy field water is 84.0%?125.0%,and the relative standard deviations is1.2%?6.8%.The established methods has high sensitivity and accuracy,which can meet the detection requirements of ultra-trace organic phosphorus pesticides in water.