| As we all know,aflatoxin is one of the most toxic substances in nature,and it is mainly found in grain.Therefore,the determination of aflatoxin content is extremely important for ensuring food quality and safety.The development of aflatoxin matrix reference material is the basis for ensuring accurate and reliable aflatoxin analysis test data in food,and plays an important role in the monitoring of aflatoxin.At present,the lack of related reference materials in China and the defects of foreign preparation technology make the existing reference materials difficult to meet the application requirements.In view of this situation,it is particularly important to establish a new preparation technology of aflatoxin matrix reference material.For organic purity reference materials,the application of reference materials is seriously affected by such problems as waste of raw materials during solid separation,incomplete removal and difficulty of long-term stability in solution separation.In view of these defects,this paper attempts to use a new freeze-drying technology to achieve the quantitative separation of pure reference materials.The separation of pure reference materials is replaced by the freeze-drying quantitative separation in liquid solvent system,and the complete removal is achieved through re-dissolution in the use link.In this thesis,the preparation technology of aflatoxin B1 matrix reference materials in peanut and the freeze-drying preparation technology of unstable purity reference material were studied.The main conclusions are as follows:1.In this paper,a new preparation technology of aflatoxin B1 matrix reference material was established.Peanuts with high fat and protein were selected as matrix,and peanuts inoculated with Aspergillus flavus were used instead of natural mouldy peanuts to ensure homogeneity and stability of toxin in the matrix.A standard strain was screened as toxigenic strain,a peanut variety with suitable toxigenic efficiency and a highly resistant peanut variety were also screened.The combined sterilization method was 110?,10 minutes and 120? for 20 minutes,the dosage of gamma-ray irradiation is 2 kGy,knife-type grinder pre-grinding,liquid nitrogen-ultracentrifugal grinding as grinding method,2%monoglyceride as emulsifier,0.02%ethoxyquinoline,potassium sorbate and carbendazim as stabilizing agent,brown glass bottle filled with nitrogen and aluminium foil bag vacuum as packing method,and-20? as storage condition.This method can effectively improve the homogeneity and stability of matrix reference materials.2.In this paper,we have studied four kinds of unstable pesticides(benfuracarb,pirimiphos-methyl,chlorpyrifos,dichlorvos)and established a new freeze-drying technology for quantitative separation of pure reference materials.The pirimiphos-methyl and dichlorvos freeze-drying recovery rates were 0 and 21.4%.The recovery rates of benfuracarb and chlorpyrifos reached to 101.5%and 103.3%.It can be concluded that the application of two pesticide varieties,benfuracarb and chlorpyrifos good and the freeze-drying recovery is complete.The relative standard uncertainty introduced by the homogeneity between the sample bottles after freeze-drying and reconstitution of benfuracarb and chlorpyrifos can better meet the accuracy requirements of the reference material.Through the accelerated stability test at 40?,it was found that the stability of the reference material of the benfuracarb solution was changed at 40? for 3 days,and the stability of the freeze-drying sample was good.The stability of the reference material of the chlorpyrifos solution was slightly decreased after storage for 15 days at 40?,and the stability of the freeze-drying sample was good.It can be concluded that freeze-drying sample stability is significantly improved compared to solution samples. |
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