Investigation Of Magnetic Extraction Technology Based On Two Magnetic Nitrogen-doped Carbon Materials

In recent years,carbon materials have attracted widespread attention due to their unique properties and huge application potential.Carbon material-based sample pretreatment techniques have been widely used for the separation and analysis of organic compounds.The magnetic carbon material combines the dual characteristics of magnetic responsiveness and high adsorption performance,so it can be used as a magnetic extraction adsorbent.Compared with the traditional sample preparation technology,the magnetic extraction technology enables phase separation by means of an applied magnetic field,eliminating the need for centrifugal filtration and making sorbents easy to recycle.When heteroatoms such as nitrogen atoms are incorporated into the lattice of carbon materials,the physical and chemical properties of carbon materials will change,making it applicable to the extraction and separation of aqueous samples.This paper mainly studies the application of magnetic nitrogen-doped carbon materials in magnetic extraction technology.Two magnetic nitrogen-doped carbon materials are prepared and applied to the selective enrichment of specific aldehydes and indoles in actual samples.The detailed research work and results are as follows:Firstly,nitrogen-doped graphitized carbon was prepared from dicyandiamide waste residue with a simple acid wash process,and Fe₃O₄/NGCB was synthesized by chemical co-precipitation method,which was characterized by XRD,SEM,EDS and VSM.Fe₃O₄/NGCB was then used as a magnetic emulsifier to construct a magnetically responsive Pickering emulsion.Several major parameters related to the extraction efficiency,such as the amount of emulsifier,oil phase volume fraction,salt concentration and p H were investigated.The results showed that for the Fe₃O₄/NGCB stable oil-in-water Pickering emulsion system,when the amount of emulsifier is 5?9mg,volume fraction of the oil phase is 30?60%,salt concentration is 2?3%and solution p H is 5,the Pickering emulsion formed is relatively stable.Secondly,a magnetic extraction with the stable magnetic responsive Pickering emulsion as“minimized extractor”was evaluated to determinate 7 aldehyde compounds?butenal,n-butenal,pentanal,hexanal,heptanal,octanal,nonanal?,combined with GC-MS/MS.The effects of magnetic emulsifier amount,extraction time,solution p H,and oil/water volume ratio on the extraction efficiency of the proposed magnetic extraction were also investigated.Under the optimized conditions,satisfactory linearities were obtained for all aldehydes,and linearity was good in the range of 1?100?g/L.The correlation coefficient was 0.9984 to 0.9998.The limits of detection and quantitation of seven aldehydes were in the range of 17.3?30.1 ng/L and54.3?103.4 ng/L,respectively.With the Pickering emulsion as a“minimized extractor,”the extraction was accomplished within 5 min.After extraction,the magnetic disperser could be recovered for reuse at least five times by an external magnetic field.The proposed method was demonstrated to be feasible,simple,and economic for the trace analysis of the aldehydes in environmental water samples.Finally,magnetic nitrogen-doped graphene was synthesized by chemical co-precipitation,which was characterized by XRD,SEM,and EDS.Several factors such as the amounts of Fe₃O₄/N-G,extraction time,salt concentration,and p H were optimized.Then a magnetic solid phase extraction with t Fe₃O₄/N-G as the magnetic adsorbent has been developed for the determination of 6 plant growth regulators?indole-3-carboxylic acid,indole-3-carboxaldehyde,3-indoleacetic acid,3-Indoleacetonitrile,3-indolepropionic acid and 3-indolybutyric acid?in bean sprout samples,combined with UPLC-MS/MS.Under the optimized conditions,six plant growth regulators?PGRs?had good linearity in the range of 1?100?g/kg,with the correlation coefficients ranging from 0.9975?0.9994.The LOD and LOQ ranged from0.1?15.2 ng/kg,0.35?42.2 ng/kg,respectively.Finally,the developed method has been successfully applied to the analysis of PGRs in five commercially available sprout samples.Attributed to the excellent performances of Fe₃O₄/N-G,the magnetic solid phase extraction process can be completed with only 10 mg of material and an extraction time of 10 s.The extractant can be easily recovered by applying a magnetic field and can be reused more than 5 times without significant fluctuations in the extraction recovery,which was suitable for analysis of plant growth regulator in bean sprouts.