Development Of Novel Analytical Methods For Edible Oil Safety

Edible oils as an important component part of people’s diet are essential consumer products in daily life. The safety of edible oils is not only related to the health of the consumers, but also directly affects the development of national economy and international trade. The establishment of accurate and reliable method for the analysis of harmful substance in edible oils has great significance to ensure food safety. It is well-known that the high fat content may cause the main difficulty in the analysis of trace amount of compounds oil matrices. Even with the advent of advanced hyphenated techniques based on mass spectrometry, these complex fatty matrices usually require extensive sample extraction and purification. Current methods with regard to pretreatment of fatty samples involve the use of one or the combination of some of the following techniques for both extraction and clean-up steps:liquid-liquid extraction (LLE), adsorption chromatography, gelpermeation chromatography (GPC), solid-phase extraction (SPE), matrix solid-phase dispersion (MSPD), etc.. However, most of these methods are tedious and time-consuming. Therefore, the development of simple, rapid and effective sample preparation method for the analysis of harmful substance with low consentration in oil matrices is desirable.In this dissertation, the author is devoted to the fabrication of novel separation materials and the development of novel sample preparation methods for quantitative analysis of trace amount of compounds in edible oils. The major contents of this dissertation are described as follows:1, The composition and characteristics of edible oils and the current situation of edible oil security in our country were simply introduced. Emphasis was focused on the extraction and purification methods for the analysis of trace compounds in oil matrices, as well as their advantages and disadvantages.2, A novel dispersive microextraction technique by combining the advantages of dispersive liquid-liquid microextraction (DLLME) and magnetic solid-phase extraction (MSPE) was proposed. In this method, a trace amount of water (extractant) was adsorbed on bare Fe3O4by hydrophilic interaction to form "magnetic water"(m-water). Rapid extraction can be achieved while the m-water was dispersed in the sample solution with the aid of a vigorous vortex. After extraction, the analyte-adsorbed m-water can be readily isolated from the sample solution by a magnet, which could greatly simplify the operation and reduce the whole pretreatment time. It was worth noting that in the proposed method water was used as extractant and Fe3CO4was served as the supporter and retriever of water. This novel method might be applicable to the extraction of hydrophilic analytes such as polar small organic molecules and metal ions from a hydrophobic sample matrix, including edible fats and oils, fatty foods, and biological samples with high amounts of lipids. The efficiency of this technique was proved by extraction of organophosphorus pesticides and3-monochloropropane-1,2-diol from several vegetable oils.3, A new sorbent for magnetic solid-phase extraction, alendronate sodium (ANDS) modified Fe3O4magnetic nanoparticles(Fe3O4@ANDS), was easily prepared via a two-step strategy. FesO4was synthesized by a solvent-thermal process, and then ANDS was grafted onto the surface of Fe3O4via the strong Lewis acid/base interaction. The resultant material was characterized by transmission electron microscopy, fourier-transform infrared spectroscopy, and zeta potential. Due to its abundant amino functional group, the Fe3O4@ANDS was applied to extract resveratrol from peanut oil based on hydrogen bonding interaction. A rapid, convenient and efficient method for the determination of resveratrol in peanut oil and other edible oils was established by coupling with HPLC-UV analysis for the first time. The linearity range of the proposed method was2-10000ng/g with correlation coefficients (R2) of0.9992and the limit of quantification for the target resveratrol was as low as to1.0ng/g. This method maybe expect to identify the authenticity of peanut oil.4, A simple co-mixing method was proposed to fabricate magnetic humic acids (MHAs). Typically, the commercially available humic acids (HAs) were directly mixed with Fe3O4magnetic nanoparticles (MNPs) in a mortar with the mass ratio of1/1.5. Then the mixture was grinded evenly and completely, and in this process, MNPs were physically wrapped and adhered to tiny HAs particles leading to the formation of MHAs which can be separated and collected rapidly by a magnet when dispersed in a solvent. Due to the good adsorption ability of HAs towards benzo[a]pyrene (BaP), the resultant MHAs were applied for the extraction of BaP from edible oils by the mode of MSPE. Coupling with HPLC-FLD, a rapid and effective method for the determination of BaP was established, which was successfully applied to the analysis of BaP in several kinds of edible oils from local markets.5, The magnetic multiwalled carbon nanotubes (mMWCNTs) were fabricated via a simple co-mixing method based on an "aggregation-wrap" mechanism. When MNPs and MWCNTs (with mass ratio4:1) were co-mixed and vortexed evenly in a solvent (e.g., ethanol, water, acetonitrile), they could assemble into mMWCNTs spontaneously and thus be magnetically separable. The prepared mMWCNTs were employed to extract eight PAHs form edible oils which was based on π-π interaction. Parameters that affect the extraction efficiency were investigated and discussed in detail. Under the optimized conditions, a simple and effective method for the determination of PAHs in edible oils was developed by coupling with GC-MS. The whole pretreatment process was rapid, and it can be accomplished within10min. The limits of quantitation for the target PAHs were found to be0.34-2.9ng/g. The recoveries in oil sample were in the range of87.8-122.3%with the RSDs less than6.8%(intra-day) and9.6%(inter-day). This method was successfully applied to the analysis of PAHs in seven kinds of edible oils from local markets.6, Rhodamine B is an illegal additive that always used as food colorant by unscrupulous businessmen. Therefore, an efficient and high-throughput screening method of rhodamine B is of great significance to ensure food safety. In this study, magnetic humic acids (MHAs) was successfully used as a MSPE sorbent and a significant matrix of the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for the detection of rhodamine B in chili oil and other foodstuff. The results indicated that the proposed method was simple, rapid, and sensitive, which can effectively fill the blank of national testing standards of rhodamine B.