| The development of sample pretreatment has always been a hot point in the field of analysis.In recent years,with the increasingly serious environmental problems,there is an urgent need for the rapid and accurate analysis method which can be widely applied for determination of the targets in different environmental matrices,such as water,atmosphere and soil.In the environmental analysis,the first step is to select an appropriate pretreatment method for purification and enrichment due to the complexity of matrices and the trace existence of the targets in the matrices,Carbon nanomaterials,including carbon nanotubes,graphene and carbon nanospheres,are emerging adsorbents.Attributed to the unique structural characteristics and huge specific surface area,they have been widely used for the enrichment and separation in environmental analysis.Chiral drugs refer to the drugs with one or more chiral centers in the molecule.Generally speaking,a pair of enantiomers have same physicochemical properties.When chiral drugs enter the environment,the degradation behaviors of the enantiomers are affected by the environmental factors(illumination,pH,microbial action,etc.),leading to the different degradation rates of the enantiomers in the environment.While in organisms,the absorption,metabolism,excretion of the enantiomers,and even the toxicity are always different;that is to say,there may be some differences in the ecotoxicity between the enantiomers of chiral drugs.Therefore,it is of great significance to study chiral drugs in the environment at the enantiomeric level.Separation and purification based on magnetic adsorption materials is a new research direction in the sample preparation.By introduction of the magnetic properties into carbon nanomaterials,we can obtain the magnetic absorbents with high adsorption capacity and magnetic response characteristics.When these magnetic adsorbents are used for extraction,the treatment of large-scale samples could be completed in a short time,which greatly simplifies the extraction process.In this paper,carbon nanotubes,graphene and carbon nanospheres were decorated with magnetic nanoparticles(Fe3O4 MNPs)by the simple self-assembly or chemical coprecipitation to prepare the magnetic nano-adsorbents with high adsorption and magnetic separation properties.Several chiral drugs(pesticides)in the environmental water samples were extracted by magnetic solid phase extraction(MSPE),followed by the enantiomeric determination with chiral LC-MS/MS.In addition,to explore the adsorption mechanism of carbon nanomaterials,graphene was selected as the model adsorbents and a series of 2-arylpropionic acids were selected as model adsorbates to carry out the adsorption equilibrium experiments.Based on the experimental results,the impact of solvent effects and adsorbate structural features on the adsorption capacity were throughly discussed.With the help of computer molecular simulation technique,the adsorption mechanism of graphene was further investigated at the molecular level.The main contents of the paper are as follows:1.Enantiomeric determination of five beta-blockers in three environmental water samples by MSPE combined with chiral LC-MS/MSFe3O4 MNPs were first synthesized by hydrothermal method.Mag-MWCNTs were then prepared via the self-assembly between Fe3O4 MNPs and MWCNTs,and used as the adsorbent for extraction of atenolol,metoprolol,esmolol,pindolol and arotinolol in three environmental water samples,followed by the simultaneous enantiomeric determination of five beta-blockers with chiral LC-MS/MS.During the MSPE process,the factors that affect the extraction efficiency were throughly investigated,such as the adsorbent amounts,time of adsorption and desorption,pH and ionic strength of the solution,types and volumes of the eluents,etc.During the enantiomeric separation,different types of chiral columns were tested for enantioseparation,and the α-glycoprotein column was ultimately selected.The mobile phase conditions(types and concentrations of the buffer salts,pH values and flow rates,etc.)were optimized.Under the optimum conditions,the extraction efficiency of the five beta-blockers was above 85%,and the theoretical enrichment factor was 1000.Method detection limits and quantitation limits were 0.50-1.45 ng/L and 1.63-3.75 ng/L,respectively.The recovery was between 82.9%and 95.6%,and the relative standard deviation(RSD)values of the intra-day and inter-day precision were below 10.4%and 7.4%,respectively.2.Enantiomeric determination of seven imidazole antifungals in three environmental water samples by MSPE combined with chiral LC-MS/MSFe2+ and Fe3+were in situ coprecipitated with graphene under alkaline condition,forming the Fe3O4 MNPs loaded on the surface of graphene.The graphene/Fe3O4 composites were used as adsorbent to extract seven imidazole antifungals in three environmental water samples by MSPE,including ketoconazole,econazole,miconazole,butoconazole,sertaconazole,fenticonazole and isoconazole.Chiral LC-MS/MS was then used for enantiomeric determination of seven imidazole antifungals in three water samples.During the extraction process,the used adsorbent amounts,time of adsorption and elution,pH and ionic strength of solution,types and volumes of eluents were optimized.Chiralcel OJ-RH column with good enantioselectivity for seven drug enantiomers was selected for separation.The mobile phase conditions were also optimized.Under the optimum condition,the extraction efficiency of seven imidazole fungicides was above 80%.The sensitivity of the method was high,and detection limits and quantitation limits were 0.11-0.32 ng/L and 0.28-0.67 ng/L,respectively.The recovery was in the range of 70.2-92.3%.The RSD values of the intra-day and inter-day precision were below 12.0%and 10.1%,respectively.3.Enantiomeric determination of five 2-arylpropionic acid anti-inflammatory drugs in three environmental water samples by MSPE combined with chiral LC-MS/MSIbuprofen,flurbiprofen,pranoprofen,indoprofen and loxoprofen sodium were extracted by MSPE with magnetic graphene as adsorbent.Chiral LC-MS/MS was used for enantiomeric determination of five drug in three environmental water samples.In the extraction process,the effects of the used adsorbent amounts,adsorption and elution time,pH values and ionic strength of the solution,types and volumes of the eluents on the extraction efficiency were systematacially investigated.Chiralcel OJ-RH column was used for simultaneous enantioseparation of five 2-arylpropionic acid drugs.The types and proportions of mobile phase,flow rates and pH of the aqueous phase were optimized.Under the optimum condition,the extraction efficiency of the five 2-arylpropionic acids was above 80%.Method quantitation limits were in the range of 8.49-26.3 ng/L.The relative recovery was 73.6-90.2%,and RSD values of the intra-day and inter-day precision were less than 9.7%and 10%,respectively.4.Enantiomeric determination of eight triazole fungicides in the environmental water samples by MSPE combined with chiral LC-MS/MSCarbon nanospheres modified by Fe3O4 MNPs were prepared via the self-assembly.The magnetic carbon nanospheres were used as adsorbent to extract eight triazole fungicides from two environmental water samples,including penconazole,uniconazole,paclobutrazole,triazolone,tebuconazole,hexaconazole,triticonazole and epoxiconazole.Chiral LC-MS/MS was used for enantiomeric determination of eight fungicides in the water samples.In the extraction process,the factors that affect the extraction efficiency,such as the amounts of adsorbent,adsorption time,pH and ionic strength of the solution,types and volumes of the eluents,as well as the eluting time were investigated.During the enantiomeric separation process,eight triazole fungicides were simultaneously separated by Chiralpak IC column,and the mobile phase conditions were optimized.Under the optimum condition,the extraction efficiency of eight triazole fungicides was above 80%.Method quantitation limits were 0.56-7.0 ng/L.Relative recovery was in the range of 77.8-93.5%,and RSD values of intra-day and inter-day precision were less than 9.8%and 7.9%,respectively.5.Adsorption experiments and computer molecular simulation for investigation of the adsorption mechanism of grapheneGraphene sheets are the basic units of carbon nanotubes,graphene,carbon nanospheres and other carbon nanomaterials.Therefore,the single layer graphene was selected as model adsorbent to investigate the adsorption mechanism of carbon nanomaterials.Six 2-arylpropionic acid compounds,including ibuprofen,ketoprofen,naproxen,pranoprofen,indoprofen and carprofen were selected as model adsorbates to complete the adsorption experiments.The impact of solvent effects and molecular structural features on the adsorption behavior were discussed in detail.It was indicated that the adsorption strength of six 2-arylpropionic acids onto graphene mainly depended on the individual aromatic structural features(the size of π-conjugated systems),rather than the hydrophobic properties of the molecules.Further,combined with the computer molecular docking technique,we also explored the interactions responsible for the adsorption of six 2-arylpropionic acids onto graphene,and depicted the possible adsorption molecular models between them. |
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