Studies On The Preparation Of Magnetic Composites And The Determination And Separation Of ?-aminobutyric Acid

Gamma-aminobutyric acid(GABA)is a kind of non-protein amino acid,as well as a kind of neurotransmitter.GABA is closely related to the occurrence and development of diseases related to the nervous system and plays an irreplaceable role in the diagnosis and treatment of psychiatric diseases.GABA is also involved in the synthesis and release of hormones in the immune system and the process of expanding the heart and brain vessels to regulate blood pressure.Because of the important physiological effects of GABA,it has been gradually developed into functional food and drugs for health care and treatment of diseases.Though GABA can be prepared using many methods,the separation of GABA from the complex matrix is vital and difficult.The existing separation methods cannot meet the requirements of rapid separation of GABA on a large scale due to the complex pretreatment process,expensive equipments,high consumption of organic solvents or time and energy,and the requirements of separation environment and operators.Therefore,the development of efficient and rapid separation and purification methods can guide the production activities related to GABA.The improvement of production technology can promote market equity.To this end,the following exploration was made in this thesis:1.In order to accurately evaluate the separation performance of the prepared material,the determination method of GABA was studied.Amino acids can be colored with ninhydrin,the colored products can be measured in the visible area,the requirements of the instrument are low.However,determination conditions reported by different literature are not the same,the main differences are the acidity of the system,the amount of chromogenic agent,the temperature and time of heating.In order to establish an accurate quantitative detection method for GABA,the influence of solvent was firstly studied in this paper,and the impact of color rendering conditions was systematically explored.The results showed that when p H=7.0,GABA and 1.8 g/L ethanol solution of ninhydrin were placed in boiling water bath for 60 min,the absorbance of the colored product produced by the reaction at 567 nm had a good linear relationship with the concentration of GABA within the range of 0.5?80 mg/L(R²=0.9998).The results provided an optimum condition for the determination of GABA and laid a foundation for the following work.This method has good reproducibility and certain selectivity.Combining with TLC,it has high accuracy in analyzing and verifying the results of food additive samples.The method can not only be used for the direct quantitative detection of GABA in some samples,but also provide a detection way for liquid chromatography.This simple,quick and visible detection method is of great significance for the guiding of production and product quality inspection under the circumstance that GABA is increasingly concerned and widely used.2.Due to the good hydrophilicity of GABA,it is difficult to be absorbed from aqueous solution for the rapid separation of GABA in a complex matrix.In this paper,the Fe₃O₄ magnetic nanoparticles coated by the polymerization were used as the magnetic polymer separation carrier,and the organic layer on Fe₃O₄@St surface was sulfonated by chlorosulfonic acid to successfully prepare the magnetic composite material(Fe₃O₄@St-SO₃H),which was rich in sulfonic acid groups on the surface.And it was applied to the adsorption of GABA.Fe₃O₄@St-SO₃H were characterized by TEM,FTIR,XRD,TG and BET.By optimizing the preparation and adsorption conditions of the material,the final adsorption rate of Fe₃O₄@St-SO₃H material for GABA reached 89.03%.The adsorption of magnetic composite Fe₃O₄@St-SO₃H on GABA is the result of multiple adsorption mechanisms,which belong to monolayer-homogeneous physical adsorption.The maximum adsorption capacity was 127.3 mg/g,when the adsorbent was used to adsorb GABA.Through the study of eluent and elution method,it was found that GABA adsorbed on Fe₃O₄@St-SO₃H surface can be eluted by shaking for 1 h at 20?in PBS(0.3 mol/L,p H=7.0),and the elution rate reached 97.54%.Moreover,the adsorption rate for GABA was still above 75%after the Fe₃O₄@St-SO₃H material was reused for 10 times,which showed excellent performance for reuse.Finally,the magnetic composite Fe₃O₄@St-SO₃H was used to separate GABA from mulberry leaf and wheat bran samples.The relative content of GABA in the solution before and after adsorption and elution was detected by LC-MS.It was found that the adsorption rate of GABA from mulberry leaf and wheat bran samples by Fe₃O₄@St-SO₃H magnetic composite was 87.61%and 89.35%respectively,and the concentration factor were 3.99 and 3.97respectively.The Fe₃O₄@St-SO₃H magnetic composite material can not only be used for rapid magnetic separation and purification of GABA in a complex matrix,but also be used for sample preparing before detection.3.In order to realize the adsorptive separation of GABA with high selectivity,the magnetic molecular imprinting polymers(Fe₃O₄@SiO₂ MIPs)was successfully prepared by combining the highly paramagnetic Fe₃O₄ nanometer materials with the highly selective Molecular imprinting technology(MIT),with GABA as the template molecule and SiO₂as the imprinting layer with high biocompatibility.Preparation and adsorption conditions of the materials were optimized,and the materials were characterized by TEM,FTIR,etc.The thermodynamics and kinetics studies of the adsorption showed that the maximum adsorption capacity of the magnetic nano-imprinted polymer for GABA was 36.05 mg/g.The exploration for eluention indicated that GABA on the surface of Fe₃O₄@SiO₂ MIPs can be eluted by 0.1 mol/L HCl without damaging the structure and adsorption performance of Fe₃O₄@SiO₂ MIPs,and the Fe₃O₄@SiO₂ MIPs still show good performance for the adsorption of GABA after being reused for 10 times.The adsorption of Fe₃O₄@SiO₂ MIPs to GABA belongs to monolayer adsorption,the kinetic model fitting results are quasi-second-order kinetics,indicating that the behavior is not the result of a single adsorption mechanism.Comparing the adsorption of some other interfering substances between Fe₃O₄@SiO₂ MIPs and Non-imprinted polymers(Fe₃O₄@SiO₂ NIPs),it was found that the adsorption of interferences by Fe₃O₄@SiO₂ MIPs was lower than that of Fe₃O₄@SiO₂ NIPs,which indicated that Fe₃O₄@SiO₂ MIPs had better selectivity for GABA.Compared with the conventional HPLC method,this method avoids the high consumption of organic solvents in the separation process.And the requirements for separation conditions and personnel is reduced and easier to meet.This method will play a positive role in the future industrial purification of GABA in food and medicinal grade and in creating a good market environment.4.In order to eliminate the interference of other substrates in the determination of GABA,the water-soluble CdTe@SiO₂ QDS was prepared.And combined with the highly selective molecular imprinting technology,the template molecule(GABA)was immobilized by SiO₂ with high light transmittance to realize the imprinting of GABA on the surface of CdTe@SiO₂ QDs.It was found that,after optimizing the elution conditions and preparation conditions,the interaction between CdTe@SiO₂ MIPs and GABA resulted in fluorescence enhancement,and the degree of fluorescence enhancement had a certain linear relationship with the concentration of GABA.The anti-interference experiment proves that the method of detecting GABA using CdTe@SiO₂ MIPS has certain selectivity.By combining quantum dot technology with molecular imprinting technology,this work provides a new method for the selective detection of GABA and lays a foundation for the direct detection of GABA in complex samples.