Analytical Methods For Determination Of Aflatoxins Based On Graphene Materials Coupled With High Performance Liquid Chromatography

Aflatoxins are a group of mycotoxins produced as highly toxic secondary metabolites by manyspecies of Aspergillus, a fungus, the most notable ones being Aspergillus flavus and Aspergillusparasiticus. Aflatoxins are highly toxic and carcinogenic. Especially, aflatoxin B1is classified as aGroup1carcinogen by the World Health Organisation (WHO) in1993. The aflatoxin-producing fungiare widespread in nature, which leads to contamination of aflatoxins in a variety of agro products, suchas corn, peanuts, rice, vegetable oils and so on. Thus, it is a huge threat to comsuption safety of agroproducts. In recent years, strict standards and control measurements have been established to ensureagro-products quality and safety in different countries successively, which means that the requirementfor the methods for the detection of aflatoxins is getting higher the higher. Therefore, the researches onnovel methods for rapid detection of aflatoxins become more and more important.In many methods for detection and quantification of aflatoxins, sample pretreatment is stillconsidered as an important part in whole analytical procedure, which needs to pay much attention.Especially for complex samples, it may even become a bottleneck point in the whole analysis process.Many agro products with low content of aflatoxins have a high oil content and complex matrix, whichfurther increases the difficulty of aflatoxins analysis.For solving such problems, in this study, new nanomaterials--graphene and its derivatives areused as adsorbents for aflatoxins coupled with HPLC to establish new methods for detecting aflatoxins.The new methods can be the technical support for monitoring studies of aflatoxins in agro products. Themain research contents and innovative points are as follows:1. Three kinds of nanomaterials were successfully synthesized. And their morphology and structurewere also studied. Graphene oxide (GO) was synthesized by chemical oxidation of graphite powder.Silk-like GO sheets showed a thickness of0.8~1.1nm, with a layer size of0.1~2μm. A series ofGO-SiO2nanocomposites were prepared by two ways. The SEM results proved that GO wassuccessfully grafted on the silica nanoparticles. The results also indicated that GO acted as inorganicglue to bind the small silica nanoparticles together. A magnetic graphene material with a one-stepsolvothermal method was synthesized by introducing a ferrous precursor in GO solution. The XRD andSEM results showed that the Fe3O4magnetic beads with a diameter of100nm are uniformly attachedon the graphene sheets.2. The tests were performed to evaluate the ability of graphene oxide (GO) as the adsorbent toadsorb aflatoxins B1. And the GO was successfully applied in detoxifying of aflatoxins in ediblevegetable oils. The research also found that it took4hours for GO to adsorb aflatoxin B1to achieveadsorption equilibrium. The maximum adsorption capacity for GO is62.5ng/mg. The GO can notonly adsorb aflatoxin B1but also a certain content of aflatoxin B2. The recoveries of the GO adsorptionof aflatoxin B1in actual oil samples ranged from97.8to98.8%, indicating that GO was suitable for removing aflatoxins in edible vegetable oils.3. Graphene oxide was synthesized and selected to be applied as an effective adsorbent fordetermination and quantification of aflatoxins in peanuts by HPLC. The limit of detection of thismethod ranges from0.08to0.65μg/kg. The limit of quantification of this method ranges from0.25to2.0μg/kg. Good linear relationships have been obtained with the correlation coefficient (r) ranging from0.99217to0.99995. The recoveries of the four aflatoxins in peanut samples are in the range from85.1%to100.8%with the relative standard deviations between2.1%and7.9%, indicating that this method wassuitable for real sample analysis.4. A method for detection aflatoxins in rice and corn has been developed by using GO-SiO2nanocomposites as the extraction material in SPE. In this method, four aflatoxins can be detected with agood linear in the range of0.5~50μg/kg. The values of the correlation coefficient between0.99956~0.99994have been achieved. The limits of detection of this method for four aflatoxins are inthe range of0.05~0.5μg/kg with the limits of quantitation in the range of0.2~2.0μg/kg.5. The vegetable oils were extremely viscous. Therefore, the solid materials for extraction aredifficult to separate from the liquid sample solution. A MSPE method was optimized to successfullyextract two aflatoxins in vegetable oils. In this method, for aflatoxin B1, a linear detection range of0.85~51μg/kg was found with a detection limit of0.85μg/kg. For aflatoxin B2, the new detectionmethod has a larger linear detection ranging from0.22~66.99μg/kg with a detection limit of0.22μg/kg.The limits of quantitation for aflatoxin B1and B2were2.64and0.66μg/kg respectively.