Magnetic Carbon-based Functional Composite Nanomaterials Combined With Direct Ionization Mass Spectrometry For Rapid Analysis Of Residual Antibiotics In Food Samples

Mass spectrometry（MS）can depict the chemical composition from samples,which possesses excellent sensitivity,high speed,and marvelous selectivity for the specific application in food safety,environmental monitoring,criminal investigation,life science and other wide fields.With the continuous development of mass spectrometry,it is a great breakthrough to combine chromatographic separation with mass spectrometry in the field of analysis.Yet,these traditional analytical methods could not cater for the demand of rapid and high-throughput analysis of mass spectrometry due to the complex and time-consuming sample pretreatment.Therefore,direct analysis of samples by mass spectrometry is an imperative topic in research.Ambient ionization mass spectrometry（AMS）,or termed as direct ionization mass spectrometry,has the ability to directly obtain the molecular information from various samples in real-time with minimal or no sample pretreatment.However,especially in the determination of trace target analytes in samples,the sensitivity,stability and accuracy of AMS are still challenging.Recently,with the rapid progress of functional materials,a strategy called the combination functional materials with ambient ionization mass spectrometry is introduced,which can access to the ability of significant improved detection by AMS.In particular,carbon-based functional composite nanomaterials have been widely used in the field of analytical chemistry due to its great potential in the effective enrichment of target analytes prior to direct ionization,so as to make rapid detection of trace components come true from complex samples.In this paper,magnetic carbon-based functional composite nanomaterials are mainly applied to the analysis technology of direct ionization mass spectrometry to realize the rapid detection in food safety.The main research contents are as follows:（1）An original method based on magnetic multiwalled carbon nanotubes（Fe₃O₄-MWCNTs）coupled with internal extractive electrospray ionization tandem mass spectrometry（iEESI-MS/MS）was exploited for fast determination of five sulfonamides（SAs）antibiotics in tap water and drinking water samples.The synthesized Fe₃O₄-MWCNTs were prepared according to hydrothermal synthesis method and used as sorbents to capture the target molecules from water sample.Then the composite nanomaterials were on-line eluted with appropriate solvent,in the meantime,and target molecules were lastly ionized and detected by iEESI-MS.Some critical parameters were investigated and optimized.With the optimum conditions,this method showed low limits of detection（LODs）ranging from 1.61 to 2.65 ng L^-1 and admirable recoveries ranging from 87.6 to 107.0%with relative standard deviations（RSDs）of less than 8.2%.The inter-and intra-day recoveries were respectively obtained ranging from 90.3%to 105.0%and from 89.7%to103.0%,while RSDs were less than 6.8%and 7.3%,respectively.These results held considerable promise for the detection sulfonamide antibiotics of various water samples by Fe₃O₄-MWCNTs-iEESI-MS/MS with high rapid and high sensitivity,confirming the latent value of this method in the water safety.（2）Enrichment of sulfonamide antibiotics（SAs）from raw milk based on magnetic multiwalled carbon nanotubes.And then SAs were analyzed by direct electrospray ionization tandem mass spectrometry（dESI-MS/MS）.First of all,The Fe₃O₄-MWCNTs composites were applied to the capture of sulfonamide antibiotics in untreated milk.Secondly,acetonitrile and deionized water were used to remove the residual milk matrix from the composite nanomaterials loaded with antibiotics.Then,nanomaterials loaded with antibiotics eluted with an optimized electrospray solvent.Under the electric field of 3.2 k V,these target compounds were ionized and analyzed by dESI-MS/MS.Under the optimized experimental conditions,this method was used to the quantitative analysis of sulfonamides antibiotics in raw milk without tanglesome pretreatment.In conclusion,the method has the advantages of low detection limit(0.013-0.024μg L^-1)and high recoveries（83.5%-103.0%）,showing that Fe₃O₄-MWCNTs-dESI-MS/MS could provide a new method for rapid detection of trace SAs in milk.