Preparation Of Carbon Nanotube Based Magnetic Composites For Separation And Analysis Of Pesticides In Food

Magnetic separation technology has fast feature, carbon nanotube has a high specific surface area, molecularly imprinted polymer has selective adsorption capacity. The omposite materials obtainted in this work were used for food analysis, in order to solve the problem encountered in the analysis of pesticide residues in complex samples. The main contents are as follows:(1) Magnetic carbon nanotubes have been synthesized by chemical deposition of Fe3O4 nanoparticles onto carbon nanotubes. They were characterized by Fourier transform infrared spectroscopy, scanning electron microscope, X-ray diffraction and physical property measurement system. The magnetic carbon nanotubes were used as the sorbents for the extraction of pyrethroids including beta-cyfluthrin, cyhalothrin and cyphenothrin from tea samples. The extraction conditions, such as the amount of magnetic sorbent, shaking time and rate, washing and eluting solution have been fully investigated. The analytes desorbed from magnetic carbon nanotubes were determined by HPLC. The relative standard deviations of within-and between-day range from 3.5% to 6.4%, and from 4.5% to 7.3%, respectively. In all three spiked levels (0.05,0.5 and 5μg·g-1), the recoveries of pyrethroids are in the range of 82.2%-94.4%. This method is much faster and more effective than traditional methods, and it is promising for the analysis of pesticides residues.(2) Magnetic molecularly imprinted polymers (MMIPs) based on carbon nanotubes were prepared using acephate as template molecule. They were characterized by infrared spectrometry, transmission electron microscopy, and vibrating sample magnetometry and employed for the isolation of acephate from cabbage, spinach, lettuce, leeks, and celery. Kinetic and recognition studies were carried out in order to investigate the adsorption properties of the polymers. The acephate was determined by high performance liquid chromatography. The recoveries of acephate at three fortified concentrations (0.015,0.15, and 1.5 mg·kg-1) were between 89.2% and 93.4%. The relative standard deviations of intra-and inter-day precision were 1.1% to 5.9% and 2.7% to 6.4%, respectively. The developed method was demonstrated to be rapid and selective for the extraction and determination of acephate in vegetables.(3) Magnetic molecularly imprinted polymers (MMIPs) were prepared with propoxur as template and carbon nanotubes as support. They were used for the preconcentration and separation of the carbamates propoxur, pirimicarb and promecarb in fruits. The effects of the amount of magnetic sorbent, shaking time and rate, eluting solution on the extraction efficiency were studied. The processes of adsorption and desorption occur within 25 min, and the MMIPs can be collected by applying an external magnetic field. The MMIPs were characterized by using FTIR, transmission electron microscopy, and vibrating sample magnetometer. The MMIPs were successfully applied to enrich and determine the carbamates in spiked homogenates of apples, oranges and pears. The pesticides were quantified by HPLC, recoveries of spiked samples ranged from 90.5% to 98.6%. The method is selective and convenient.