Research On The Determination Of Estrogens In Food

Estrogens can maintain the stability of the endocrine system, thus, it is very significant to monitor the hormone levels of mammalian in clinical disease prevention, diagnosis and treatment. At present, the abuse of estrogens in animal fattening or growth promotion is serious. Many hormone residues in animal products and environmental pollutants and these compounds have adverse effects on the endocrine system in humans and environment. Therefore, the establishment of an accurate, simple, and efficient method for the determination of estrogens is particularly important. In this paper, we have studied several methods based on high performance liquid chromatography to determine17β-estradiol (βE2), estrone (E1), estriol (E3), and diethylstilbestrol (DES). The main research contents are as follows:Chapter1Determination of estrogens in pork by vortex-assisted dispersive liquid-liquid microextraction combined with high performance liquid chromatography-fluorescence detectionIn this method, nonanoic acid was used as extration solvent, and vortex-mix instead of organic dispersive solvent was applied to assist the dispersion of the extraction solvent into aqueous samples for extraction and preconcentration of three estrogens (estriol (E3),17β-estradiol (βE2), estrone (El)) in pork. Due to the elimination of dispersive solvent, high extraction efficiency and enrichment factor could be achieved. Using high performance liquid chromatography-fluorescence detection improved sensitivity of the method. The optimum conditions of VA-DLLME was:3%(v/v) nonanoic acid, vortex-mix1min and centrifugation at3000rpm for5min. Linear calibration curves obtained by plotting the peak area against the concentration of the respective compounds were found to be linear over the range of0.1-1000ng mL"1for all estrogens. The limits of detection (LOD) were0.01ng mL-1for E3,0.01ng mL-1for βE2and0.06ng mL-1for El, respectively. Recoveries of the estrogens in spiked human urine samples were in the range of96.8to102.3%and the relative standard deviations (RSD%, n=5) were less than2.98%.Chapter2Vortex-assisted hollow fibre liquid-phase microextraction technique combined with high performance liquid chromatography for the determination of estrogens in milk samples A HF-LPME method using nonanoic acid as extracting agent and vorex-mix was applied to assist the dispersion was developed. The mehod can be completed at room tempreture. Compared with traditional stirring hollow fibre liquid-phase microextraction, the nolve method is simple, effecient, and the enrichment factor can be achived to330. The optimum conditions of VA-HF-LPME was:4cm hollow fibre,vortex-mix5min, pH4.0. The results shown that the linear calibration curves obtained by plotting the peak area against the concentration of the respective compounds were found to be linear over the range of5-1000ng mL-1for three estrogens. All correlation coefficients of the calibration curves were higher than0.998, and the relative standard deviations (RSD%, n=5) were2.28-4.38%. The limits of detection (LOD) were0.06-0.17ng mL-1. Recoveries of the estrogens in spiked milk samples were in the range of87.68-94.25%. The method was successfully applied for determination and preconcentration of estrogens in milk samples.Chapter3Supramolecular solvent-based vortex-assisted hollow fibre liquid phase microextraction combined with high performance liquid chromatography for the determination of estrogens in milk samplesThis method breaks the classic single organic solvent and choses a nolve supramolecular solvent as extraction solvent for hollow fibre liquid phase microextraction and combined with high performance liquid chromatography for the determination of estrogens in milk sample. Ionic liquids1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4), n-octanol, and water composed supramolecular solvent in situ and instantaneously. Estrogens were extracted on the basis of hydrophobic and the formation of hydrogen bonds and Van der Waals forces. Hydrogen bond was confirmed by1H,2H NMR and infrared spectroscopy. Results shown that the supramolecular solvent has highly compatible with estrogens and HPLC. The method was successfully applied for determination and preconcentration of estrogens in milk samples. The proposed technique provided shorter equilibrium time (4min), good linearity (>0.9985), low limits of detection (0.10-0.22ng mL-1), high recovery (88.9-94.05%), and good repeatability (RSD%=1.24-4.36).