Preparation Of Deep Eutectic Solvents And Their Applications In Analysis Of Some Food And Chinese Herbs

Research and development of new effective and reliable methods for food analysis is the key to ensure food safety.Applying biocompatible solvent and nanomaterials to construct simple sample pre-treatment technology and online analysis of separation technology is a top priority.Deep eutectic solvent(DES)with some pollution-free,cheap,controllable physico-chemical properties and other characteristics were paid much attention in pretreatment and analysis of food samples.In our study,a series of deep eutectic solvents was developed and applied to separation and analysis of some food constituents and bioactive components,and some separation related mechanisms were discussed.The main results are as follows:1.Research on ultrasonic-assisted DES microextraction method and its application in determination of plant growth regulators in edible vegetable oil samplesSix DESs were prepared by mixing choline chloride,tetramethyl ammonium chloride,tetraethyl ammonium chloride and tetrabutyl ammonium chloride with ethylene glycol,glycerol and urea,respectively.A DES-based microextraction method was built by applying the well hydrophilicity of DES into forming two non-dissolved phase between DES and n-hexane or oil phase.Under the optimal extraction conditions with heating and ultrasound,the contents of three plant growth regulators in edible vegetable oil samples were calculated.The results showed that the limits of detection of Indole-3-acetic acid,3-indolebutyric acid and 4-iodophenoxyacetic acid were 60,20 and 10 times lower than unextracted.The recoveries were in the range of 72.7-108%,which can meet the analytical requirements of real samples.The proposed liquid phase microextraction method can simplify the complex sticky oil pretreatment process and make an achievement of extraction and enrichment for these three plant growth regulators.2.Preparation of DES-CNNs composites and its application to analysis of antioxidants in edible vegetable oil samplesEleven composites were prepared by layered structure of graphite-like carbon nitride nanosheets(CNNs)and different DESs under sonication and heating condition.The composites were characterized by SEM?TEM?XRD?FT-IR?BET and EA.Experiments were carried out to separate and enrich four phenolic antioxidants(propyl gallate,tert-butylhydroquinone,butylated hydroxytoluene and octyl gallate)in eleven edible vegetable oil samples.Several conditions including type of composites,extraction temperature,time and volume of extractant were optimized.The results demonstrated that a composite consisted of CNNs and a DES forming by choline chloride with lactic acid can achieve best extraction factors of PG,TBHQ,BHA and OG with the help of 60°C heating extraction for 40 min.Good linearities for PG,TBHQ,BHA and OG were in the range of 0.02-0.50 ?g/m L,recoveries were between 50.0% and 133% with relative standard deviation of 0.32-9.21%.3.Research on DES-based extraction method of cordycepinAiming at high efficient extraction of cordycepin in cordyceps militaris,experiments were carried out to investigate DES extraction effect by applying HPLC technique.Comparisons were made among DES,water and methanol,which demonstrated that the extracting efficiency of using DES was twice more than using water,when the extraction procedure carried out at 60°C for 40 min with material-to-liquid ratio at 1:200.4.Research on deep eutectic solvents as a mobile phase modifier for high-performance liquid chromatography(HPLC)and its application in analysis of alkaloids.Alkaline compounds with similar structure confronts separation difficulties on a C18 column,including peak width and peak tailing.Seven DESs were prepared by mixing ethylene glycol with different hydrogen-bond acceptor(choline chloride,tetramethyl ammonium chloride,tetraethyl ammonium chloride and tetrabutyl ammonium chloride)and by mixing choline chloride with different hydrogen-bond donor(urea,citric acid and glycerol),respectively.The effects of organic solvents,the concentration of DES,types of DESs and column temperature were investigated in detail.After that,a novel DES modified mobile phase system was established as 32:68(v/v)acetonitrile-1.0% DES(p H 3.3),which was applied to separate quaternary alkaloids(berberine chloride,sanguinarine,chelerythrine and coptisine chloride)on a C18 column.From the research results,it is found that when a small amount of DES was added in the mobile phase,noticeable improvements were distinctly observed such as improving resolution and decreasing peak tailing.Then,DES modified RP-HPLC mobile phase system was successfully applied to determine the content of alkaloids in Chinese herbal berberine chloride samples and achieved recoveries from 90.6% to 99.1% with relative standard deviation in the range of 0.62-2.81%.Based on the investigation of separation factors,the experimental results demonstrated that the mechanism of DES as mobile phase modifier was contributed to the synergistic effect between both hydrogen-bond acceptors and hydrogen-bond donors.5.Research on deep eutectic solvent as a mobile phase modifier for hydrophilic interaction liquid chromatography(HILIC)Taking choline chloride as a hydrogen-bond acceptor and ethylene glycol as a hydrogen-bond donor to prepare a uniform and transparent DES at the molar ratio of 1:3,and the formed DES is liquid at room temperature.In our experiment,a Si O2 column(150 mm × 4.6 mm,3 ?m)was selected for separation and DES modified HILIC mobile phase system was a mixture of acetonitrile and DES with different volume fraction.Subsequently,the concentration of DES in acetonitrile as well as the column temperature on the effect of separation were investigated.According to the research results,it is found that better separation of four nucleobases(uracil,6-chlorouracil,cytosine and hypoxanthine)and two nucleosides(adenosine and cytidine)was obtained by using acetonitrile and DES mixed solution as a mobile phase system than that using traditional water-based solution.A baseline separation between cytosine and cytidine can not be achieved by HILIC with water-based mobile phase,however,greater improvent was gained by applying HILIC with modified DES-based mobile phase.Meanwhile,the retention times of four nucleobases and two nucleosides decreased as the proportion of DES in acetonitrile increased,the most significant decrease of which was with cytidine.Similar retention behavior took place with the effect of column temperature.Decreased retention times of the analytes were observed as column temperature increased.The experimental results confirmed that DES has the remarkable ability for modification of HPLIC mobile phase and the modified system was stable and reliable.