| Milk is rich in nutritional value, which contains large amounts of proteins, fat and vitamins. It is important in our daily life. With frequent occurrences of food safety issues, great attention has been paid to the safety of milk. Environmental estrogens, which are widely found in the nature, can interfere with the normal endocrine of the organisms and harm the health of organisms. The environmental estrogens can accumulate in the body, which means the levels of environmental estrogens in the milk and dairy products may be excessive. Therefore, it is of practical significance to detect the environmental estrogens in the milk and dairy products. In this paper, two sample pretreatment methods have been established to extract environmental estrogens in milk and dairy product samples. The thesis is divided into three chapters, the contents are as follows:Chapter 1: The hazards of environmental estrogens and the sample pretreatment methods for the determination of environmental estrogens are outlined; the background and content of this work were elaborated.Chapter 2: In this part, a salting-out assisted liquid- liquid extraction method coupled with low temperature purification for the analysis of bisphenol A, octylphenol, nonylphenol, diethylstilbestrol and 17β-estradiol in milk and infant formula by UHPLC-MS/MS were investigated. The acetonitrile and water phases were separated by salting-out assisted liquid- iquid extraction, and the target analytes were transferred to the acetonitrile phase. The fat and the remaining water in the matrix were removed by low temperature purification, and the polar impurities were removed by an SPE cartridge containing neutral alumina. Some important parameters, such as the species and amount of salting-out reagent, the volume ratio between sample solution and acetonitrile, the freezing temperature and freezing time and the amount of adsorbent were carefully investigated and optimized to achieve the best extraction efficiency. Under the optimal conditions, satisfactory extraction recoveries were obtained for the five compounds in the range of 73.50-119.23%, the correlation coefficients(R2) were greater than 0.9950 and the limits of detection were in the range of 0.03-0.23 ng/mL. The intra-day and inter-day precisions were in the range of 4.53-8.97% and 2.68-6.01%, respectively. The proposed method was successfully applied to the analysis of seven kinds of market-purchased milk and two kinds of infant formula. The proposed method is simple, easy and sensitive low detection limit.Chapter 3: In this part, magnetic solid phase microextraction(MSPME) was used for the determination of estradiol benzoate(EB) in milk and dairy products by HPLC-UV. Fe3O4-COOH magnetite nanoparticles(Fe3O4-COOH MNPs) were synthesized via a solvothermal process,and used as adsorbent to adsorb estradiol benzoate in the milk. The synthesis method of Fe3O4-COOH MNPs is simple with low cost; and the established sample pretreatment method is timesaving with the total run time of 20 min. The parameters were investigated and optimized to achieve the best extraction efficiency, such as the amount of adsorbent, the time of adsorption and desorption, the spec ies and volume of the desorbent as well as the pH of the solution. The proposed method was successfully applied to the analysis of pure milk, yogurt and milk beverage. Under the optimal conditions, satisfactory extraction recoveries were obtained for EB in the range of 80.36-103.24%, relative standard deviations were in the range of 0.90-8.31%. Limits of detection(LOD) and limit of quantitation(LOQ) were was 1.6 ng/mL and 5.4 ng/mL, respectively. The linear range was 0.008-0.4 μg/mL with correlation coefficient(R2) of 0.9998. To the best of our knowledge, it is the first time to use magnetic solid phase microextraction for the determination of estradiol benzoate in milk and dairy products. The established method is simple and timesaving with low-cost. |
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