Preparation Of Magnetic Sorbents By Physical Blending Method And Its Applicaltion In Sample Pre-treatment Of Foodstuffs

Nowadays, more and more advanced instrument analysis methods with high sensitivity are applied in environmental, food and biological sample analysis. However, in most situations, sample pre-treatment methods are still needed to reduce matrix interference and decrease detection limit. Therein, magnetic solid-phase extraction (MSPE) is the method of many merits. In this mode, powdery magnetic sorbents can be uniformly dispersed into a sample solution. At this point, the contact between the sorbents and the analytes increased greatly, which is beneficial to enhance the extraction efficiency and facilitate the mass transfer of analytes. Meanwhile, the sorbent can be reversibly agglomerated and re-dispersed in sample solution by the application of an appropriate magnetic field; thus, the phase separation could be conveniently conducted. Compared with solid phase extraction (SPE) or fiber solid-phase micro-extraction, MSPE is a time-saving method; also the high backpressure caused by tightly packed SPE cartridges can be avoided, which expands its application in extracting analytes from environmental or biological samples.In order to make better use of MSPE, it is necessary to synthesis magnetic sorbents with different properties. However, procedures involved in the chemical modification are relatively tedious. To overcome this shortage, on the basis of existing synthetic method proposed by our group, the author expanded the strategy of "physical blending" to endow the non-magnetic material with magnetic operational convenience. The main contents in the dissertation are as follows:1. In chapter 2, a simple method for preparation of magnetic carbon nitride nanosheets was established, in which no chemical modification to the raw material was required. In addition, a method for the analysis of PAHs in edible oil samples was established by combination of MSPE using the prepared magnetic CN nanosheets as sorbents with gas chromatography-mass spectrometry (GC/MS) analysis.2. In chapter 3, the magnetic molecularly imprinted polymers (MIPs) were synthesized by a simple co-mixing method The two components (MIPs and Fe3O4 magnetite nanoparticles) endowed the material with manipulative convenience and good extraction capacity toward FQs in the milk matrix. This study demonstrated that the commercial MIPs can be used as raw material to fabricate magnetic MIPs sorbent by the strategy of "physical blending". The proposed MSPE method based on magnetic MIPs was rapid, convenient and efficient.3. In chapter 4.1, a magnetic material based on Fe3O4 magnetite nanoparticles (MNPs), graphitized carbon black (GCB) and primary secondary amine (PSA) were fabricated in a simple way, and the resulting material was further used as adsorbent in "clean-up" procedure in QuEChERS method. And in chapter 4.2, in order to make the method more time-saving, the author managed to integrate "extraction/partitioning" and "purification" procedures into one step MSPE. To accomplish this objective, a new magnetic adsorbent was prepared by simple physical blending five components (i.e. anhydrous magnesium sulfate, sodium chloride, GCB, PSA and MNPs) which provided various properties for the magnetic adsorbent. The magnetic "one-step" QuEChERS method integrated "extraction" and "clean-up" procedures into one step without any centrifugation process. The magnetic adsorbents with manipulative convenience facilitate phase separation of sample mixture, and at the same time can adsorb impurities. To evaluate the proposed method, it was applied for the determination of pesticide residues in freshly squeezed juice of some vegetables and fruits.4. In chapter 5, the author proposed a new hypothesis which named "collision" to explain the formation of magnetic SPE packed materials. It was proved that when the size of non-magnetic materials considerably larger than MNPs, these materials can be endowed with magnetic operational convenience by physical blending. This process is less affected by pristine surface chemistries of materials and the category of dispersants.