Mixed-mode Magnetic Adsorbents and Their Enrichment Performance of Toxic and Harmful Substances in Foodstuff

Author:Xu Fei

Supervisor:wei yin mao


Degree Year:2019





The main pollutants in foodstuff include veterinary drugs,pesticides,natural toxins and illegal additives and so on.Due to the low residual amount of various pollutants in food and the impurities such as proteins and lipids in the complex samples,the clean-up and detection progress will be seriously disturbed.Therefore,the whole process of food pollutant residues requires effective pretreatment and accurate instrumental methods.The liquid chromatography coupled to tandem mass spectrometry(LC-MS/MS)is the most practical,rapid and accurate technology.However,matrix effect is ubiquitous in LC-MS/MS detection process,which affects the reliability of detection results.Solid phase extraction is considered to be one of the most effective methods to eliminate or reduce the matrix effect.However,most of the reported adsorbents are single-mode adsorbents such as reverse phase or ion exchange,which have poor selectivity to the target substance and cannot effectively eliminate the interference of impurities and matrix effect.This paper in view of the more prominent problems in the food contaminants,according to the structure characteristics of all kinds of poisonous and harmful substances,from the perspective of the adsorbent and target mechanism,designed the four mixed-mode magnetic microspheres.The magnetic solid-phase extraction(MSPE)using mixed-mode adsorbents improved selectivity and adsorption capacity.The matrix effect in LC-MS/MS detection process was also reduced obviously.Finally,these novel adsorbents successfully applied in analysis and determination of the mushroom toxins,shellfish toxins,fluoroquinolone and opium alkaloid.The main research contents include as below:1.According to amatoxins and phallotoxins structures had the characteristics of adjacent hydroxyl except forγ-amatoxin,a new type reversed phase/boronate affinity(RP/PBA)magnetic microspheres were designed.The adsorbent showed greater adsorption capacity and selectivity for the analytes via hydrophobic,π-πand boric acid affinity effect.The proposed MSPE-UPLC-MS/MS exhibited good linear correlation(r>0.9930),with a satisfactory recovery(97.6-114.2%for mushrooms and 81.3-98.7%for urine)as well as lower LODs(0.3μg/kg for mushrooms and 0.01 ng/mL for urine).Compared with the reported clean-up methods,the MSPE operation was simple and rapid.The established analysis method had been successfully applied to the detection of a case of poisoning caused by Lepiota brunneoincarnata in Ningxia,China.2.According to the carboxyl characteristic of lipophilic marine biotoxins,the reversed-phase/weak anion exchange(RP/WAX)magnetic mesoporous microspheres were designed.The adsorbents had C188 and NH2 on their hole,which were matched with the structure of the targets,and could selectively absorb targets through hydrophobic and electrostatic forces.The adsorption capacity was higher.In addition,the detection matrix effect was eliminated.The MSPE-UPLC-MS/MS exhibited a linear correlation of0.9980-0.9991,satisfactory recovery ranged from 82.8 to 118.6%,as well as lower LODs from 0.4 to 1.0μg/kg.These results indicated that the proposed method had potential for use in the analysis of lipophilic marine biotoxins in shellfish samples.3.The strategy of the unique reversed-phase/weak cation exchange(RP/WCX)adsorbent for the enrichment and analysis of nine fluoroquinolones in complex sample by LC-QqQLIT-MS/MS was established.The RP/WCX adsorbent showed greater adsorption capacity and selectivity for the analytes with phenyl and tetrazolyl groups,which could adsorb fluoroquinolones selectively via hydrophobic,electrostatic andπ-πinteractions.The MSPE method as well as using stable isotope labeled internal standards was able to reduce the matrix effect significantly.Subsequently,the MSPE-LC-QqQLIT-MS/MS demonstrated well analytical features in terms of linearity(r>0.9960),satisfactory recoveries(88.6-118.3%)and lower LODs(0.5μg/kg).Finally,the developed method had been successfully applied to the real pork samples for food-safety risk monitoring in Ningxia,China.4.Amantadine-functionalized magnetic microspheres(Fe3O4@SiO2@ADME)were prepared and applied as reversed phase/hydrophilic(RP/HILIC)adsorbents for the enrichment and analysis of opium alkaloids in hotpot seasoning samples with LC-QqQLIT-MS/MS.The adsorbent showed greater adsorption capacity and selectivity for targets via hydrogen bond,hydrophobic andπ-πconjugative effect.The established MSPE combined with stable isotope labeled internal standards could reduce matrix effect significantly.Under the optimum conditions,LODs were in the range of 0.05-0.8μg/kg,and the recoveries were from 80.1 to 115.3%,respectively.Finally,the proposed method was successfully applied to the determination of opium alkaloids in hotpot seasoning.