Study On The Sensitivity Detection Method For Weak Electroactive Substances By Miniaturized Electrophoresis Coupled With Amperometric Detection

1.PrefaceCapillary electrophoresis?CE?has been widely used in food analysis,drug analysis and biological analysis and other fields,because of its advantages of high separation efficiency,short analysis time,small sample amounts and wide application ranges.This chapter mainly introduces the principles and devices of CE,new research progress of nanomaterials in electrochemical detection and liquid phase microextraction.In this thesis,a miniaturized CE coupled with amperometric detection?mini-CE-AD?was used to study the sensitive detection method for weak electroactive substances based on the previous studies.On the one hand,from the perspective of detection,a gold nanoparticle/reduced graphene oxide?AuNP/rGO?composite electrode was fabricated for sensitive determination of amino molecules.On the other hand,from the perspective of sample preconcentration,a method using hollow fiber liquid phase microextraction?HF-LPME?was established for selective and sensitive determination of glutathione.2.Study on determination of amino molecules by mini-CE-AD using AuNP/rGO composite electrodeIn this work,AuNP/rGO composite electrode was fabricated for detecting the main bioamines and their precursor amino acids in beer based on mini-CE-AD.The surface morphology and structure of the synthetic AuNP/rGO material were observed by scanning electron microscope,energy dispersive X-ray spectroscope,X-ray diffraction,and Fourier transform infrared spectroscopy.The analytical performance of the composite electrode was verified by cyclic voltammetry and mini-CE-AD approaches.Four target analytes?tryptamine,tryptophan,tyramine and tyrosine?were separated within 7 min in 50 mM Na₂B₄O₇-NaOH buffer?pH=9.35?at a separation voltage of 3kV.This developed method has been applied to the beer samples,and acceptable recovery could be obtained ranging from 84.5%to 108%.This AuNP/rGO composite electrode has the advantages of simple preparation and can provide good sensitivity?0.018?0.14?g/mL,S/N=3?at a low working potential?+0.65 V vs.SCE?.With fast analysis speed and good reproducibility,this method can give a promising potential application in the fields of food safety analysis and portable instrumentation.3.Study on determination of glutathione by mini-CE-AD using HF-LPMEIn this work,a method using HF-LPME was established for determination of glutathione in noninvasive fluids based on mini-CE-AD.The optimal enrichment conditions of glutathione were discussed,in which supported liquid membrane is 1-octanol,donar phase is 8 mL HCl?pH=2.86?containing 240 g/L NaCl solution,acceptor phase is 10?L 60 mM H₃BO₃-Na₂B₄O₇?pH=8.00?,extraction temperature is37?,stirring rate is 400 rpm,extraction time is 90 min,the EFs of GSH can reach 471,the limit of detection can be up to 0.46 ng/mL?S/N=3?.This developed method has been applied to saliva samples,and acceptable recovery could be obtained ranging from92.7%to 100.3%.HF-LPME has the advantages of simple device,low cost and environment-friendly.Moreover,this proposed method does not require pretreatment for saliva samples and can be directly used for injection after extracting,providing a promising potential application in the fields of noninvasive fluids sample analysis and portable instrumentation as well.