Preparation Of Graphene Oxide Composite And Its Application In The Analysis Of Neurotransmitter And Estrogen

In this thesis,graphene oxide?GO?was prepared by Hummers'method,and then GO@SiO₂nanocomposites was prepared by one-pot aggregation in aqueous phase with sol-gel technique.The structure and morphology of the GO@SiO₂ were characterized by scanning electron microscopy,transmission electron microscopy,Fourier transform-infrared spectroscopy,and X-ray diffraction.The prepared GO@SiO₂ was used as adsorbent of dispersion solid-phase extraction?DSPE?for extraction and preconcentration of target analytes.A series high-performance liquid chromatography?HPLC?methods by using GO@SiO₂ as the sorbents of DEPE for the analysis of neurotransmitter and estrogen were developed.This article was divided into four chapters.In chapter 1,generally introduced the effect of several important neurotransmitter and estrogen,the mainly used sample pretreatment methods,as well as the analysis and detection methods for neurotransmitter and estrogen.Moreover,the purpose and signification of this thesis were also described.In chapter 2,a dispersive solid-phase extraction?DSPE?with graphene oxide@SiO₂?GO@SiO₂?nanocomposites as the adsorbent followed by high-performance liquid chromatography analysis was developed for simultaneous determination of melatonin,L-tryptophan,and two L-tryptophan-derived esters in food?black sesame seed was selected in this case?.The GO@SiO₂ nanocomposites was prepared by one-pot aggregation in aqueous phase with sol-gel technique.The structure and morphology of the GO@SiO₂ were characterized by scanning electron microscopy,transmission electron microscopy,Fourier transform-infrared spectroscopy,and X-ray diffraction.The extraction conditions of DSPE including the ratio of material to liquid,adsorption and desorption time,desorption temperature as well as desorption solvents were investigated,respectively.The detection limits of the developed method for the analysis of melatonin,L-tryptophan,L-tryptophan methyl ester and L-tryptophan ethyl ester were achieved below 0.1?g mL^-1.The established method was successfully applied to the analysis of the target analytes in black sesame seed,which provided a simple,low-cost and sensitive approach for the determination of trace compounds in complex samples.In chapter 3,a method for analysis of dopamine and serotonin in serum by HPLC by using GO@SiO₂ nanocomposite as the adsorbent was established.The method was used an Agilent Eclipse Plus C18 column?3.5?m;4.6×100 mm?reversed phase column for separation.The proportion of mobile phasewas ammonium acetate buffer?phase A?:methanol?phase B?=90:10and the flow rate was set as 0.5 mL/min.The linearity,precision,recovery and detection limit of the method were verified.The DSPE-HPLC method was sucessfully applied to analysis of dopamine and serotonin in bovine serum and female rat serum.In chapter 4,a method for simultaneous determination of five estrogens?estriol,17?-estradiol,17?-estradiol,estrone and hexestrol?in environmental water by HPLC with GO@SiO₂nanocomposite as the adsorbent was developed.The samples were separated on an Eclipse Plus C18 column?3.5?m;4.6×100 mm?reversed phase column with water-acetonitrile as mobile phase.The results showed that the developed method exhibited good linearity for the five estrogens.The LODs were achieved as not higher than 0.02?g/mL based on a signal-to-noise ratio?S/N?of 3.The recoveries of method for the anlyssi of environmental water samples was between 86.7%¹07.5%under the three adding levels of 1,20,200?g/mL with relative standard deviations?N=5?was 1.7%³.8%.Two water samples from Henan University were tested and none the above five estrogens was found.The method was suitable for the quantitative analysis of estrogenic pollutants in environmental water samples.