Rapid Preparation Of Expanded Graphite By Microwave Irradiation For The Extraction Of Organic Pollutants In Food Samples

Expanded graphite(EG) is a promising material. In recent years, with the advantages of large surface area, high adsorption capacity, low cost and excellent mechanical and chemical stability, EG has been widely applied in various fields including adsorption, environmental conservation, catalyzing, cell materials and medical science. Especially in the field of adsorption, it has been regarded as ideal sorbent. In this thesis, three kinds of EGs were rapidly prepared by microwave irradiation. These EGs were used as solid-phase extraction adsorbents for the extraction of herbicide and antibiotic residues in food samples. The main contents and results of this thesis are as followed:1. EG was prepared by microwave irradiation. The preparation process was accomplished in less than 4 min. H2SO4 and H3PO4 were used as intercalating agents. X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectrometry were applied to characterize the EG. The obtained product showed worm-like morphology, had wide pore size distribution and exhibited high adsorption capacity. The EG was successfully applied as solid phase extraction(SPE) adsorbent to extract and clean up the triazine herbicides in milk, followed by liquid chromatography tandem mass spectrometry(LC-MS/MS) analysis. The parameters affecting the performance of extraction and LC-MS/MS conditions were evaluated. Under the optimal conditions, the detection limits of triazines are in the range of 0.03-0.12 ng m L-1. At the spiked level(0.4 ng m L-1), the recoveries of triazines are in the range of 82.5 ± 2.5% to 97.5 ± 7.5%. The proposed method was successfully applied to determine six triazines in six milk samples. The results confirmed that this method were sensitive and reliable.2. During the preparation of modified expanded graphite, KMn O4 was used as oxidizing agent while H2SO4 and H3BO3 were used as intercalating agents. After the microwave irradiation, the obtained modified expanded graphite was characterized by X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectrometry. And it was used as SPE adsorbent to extract chloramphenicol in egg samples, followed by LC-MS/MS analysis. Compared with the EG we prepared before, the modified expanded graphite showed higher adsorption capacity towards chloramphenicol. The parameters affecting the performance of extraction were evaluated. The detection limit of the method was 0.27 ng g-1. The results confirmed the practicality and reliability of this method.3. Expanded graphite was prepared with H2SO4 using as intercalating agents. We used acetyl sulfate as sulfonation agent to modify the surface of the expanded graphite and obtain sulfonated EG. X-ray diffraction, scanning electron microscopy and Fourier-transform infrared spectrometry were applied to characterize the sulfonated EG. There were more abundant groups on the surface of sulfonated EG. It was the first time to use sulfonated EG as SPE adsorbent to extract sulfonamides(SAs) in honey samples. The analytes eluted from the sulfonated EG was determined by LC-MS/MS. Parameters such as amount of sulfonated EG, sample p H, washing sovent and eluting conditions were optimized. The proposed method was successfully applied to determine SAs in honey obtained from local markets. The detection limits of SAs are in the range of 0.78 – 1.10 ng g-1 and the recoveries are satisfactory.