Research On The Construction Of Metalloporphyrin Electrochemical Sensor And Its Specific Detection Of Antioxidants In Plant Oils

Phenolic antioxidants are a class of food additives that can effectively inhibit the spoilage of food due to oxidation.However,excessive use or abuse of phenolic antioxidants will cause serious harm to human health.At present,the existing detection methods are difficult to meet the requirements of on-site detection and rapid detection.Therefore,it is necessary to develop a fast,convenient and efficient method for the detection of phenolic antioxidants.In recent years,electrochemical sensors have been widely used in food analysis,biomedical analysis,and environmental detection due to their advantages of high sensitivity,low detection limit,fast,convenient,and easy miniaturization.In this paper,the antioxidants of edible oils were selected as the analysis objects,and metalloporphyrin-based electrochemical sensors were constructed by designing the structure of metal centers and exocyclic substituents of metalloporphyrins.The sensor achieves highly sensitive and rapid detection of phenolic antioxidants such as tert-butylhydroquinone（TBHQ）and butylhydroxyanisole（BHA）.The research content of this paper mainly includes the following aspects:（1）Based on the excellent electrochemical properties of metalloporphyrin,a new electrochemical sensor was designed for the rapid detection of antioxidants,and the effect of metal ions in the center of metalloporphyrin on the detection performance of the sensor was studied to establish a rapid and sensitive method for the detection of phenolic antioxidant tert-butylhydroquinone in plant oil.First,the effects of five different central metal ions（Fe,Zn,Ni,Co,and Cu）on the electrocatalytic activity of metalloporphyrins were compared,and it was found that the strongest response signal was measured at the zinc tetraphenylporphyrin-modified electrode,which was 2.58times that of the bare electrode.The reasons for the high detection performance of Zn TPP were investigated by SEM,TEM,EIS and molecular simulation techniques,respectively.Meanwhile,Zn TPP was modified onto multi-walled carbon nanotubes（MWCNTs）to enhance the electron transfer between the composite and the electrode surface.The successful modification of the material was proved by characterization methods such as FT-IR,XRD and XPS.Finally,a linear relationship between TBHQ and response current was established by cyclic voltammetry.The results show that the Zn TPP/MWCNTs/GCE sensor has a wide linear range（0.01-1000μM）,a low detection limit（0.027μM）and good sensitivity(6.29μA·μM^-1cm^-2).At the same time,the sensor has good selectivity and repeatability（n=6,relative standard deviation（RSD）=1.12%）.The sensor was used to detect TBHQ in plant oil samples,and the recovery rate was 93.0%to 102.6%,and the deviation from the result obtained by HPLC was less than 2.80%.（2）A novel metalloporphyrin covalent organic framework material COF-366-Zn was prepared and used to construct an electrochemical sensor for the rapid detection of antioxidant TBHQ.First,the effects of different extra-ring substituents on the electrocatalytic activity and substrate specificity of metalloporphyrins were investigated using zinc tetraphenylporphyrin as the parent compound,and it was found that 5,10,15,20-tetrakis（4-aminophenyl）-21H,23H-porphyrin zinc（Zn TAPP）exhibited the highest electrocatalytic performance.The reason for the higher detection performance of Zn TAPP was explored based on the molecular orbital energy levels calculated by DFT general function theory.Meanwhile,in order to improve the storage stability of metal porphyrin-modified electrodes in the previous chapter,a metal porphyrin-based covalent organic framework（COF-366-Zn）was synthesized in this chapter using Zn TAPP as the template molecule.SEM,EDS,XRD,FT-IR and XPS characterization methods were used to verify the successful synthesis of the materials.Finally,the material was loaded onto MWCNTs to construct the COF-366-Zn/MWCNTs/Nafion/GCE electrochemical sensor.The results showed that the sensor was able to sensitively detect TBHQ in plant oil over a wide range（0.01-1000μM）with a detection limit of 0.022μM.The sensitivity(7.30μA·μM^-1cm^-2)and storage stability（89.52%current retention at 28 days）of the sensor were improved relative to the previous chapter.（3）An electrochemical method for the analysis of multiple phenolic antioxidants in plant oils was constructed based on the COF-366-Zn/MWCNTs/Nafion/GCE electrochemical sensor described above.First,using the COF-366-Zn/MWCNTs/Nafion/GCE electrode,it was found that simultaneous detection of TBHQ,BHA and phenol（Phenol）could be achieved by cyclic voltammetry.In addition,the mutual interference between the three analytes was investigated using differential pulse voltammetry,and a linear equation between the concentration of the third analyte and the response current was established in the presence of the other two substrates.Finally,the linear equation for simultaneous detection of TBHQ,BHA and Phenol was constructed as I_p（μA）=-0.5201 C（μM）-9.3513（0.01μM-800μM,R²=0.994）,I_p（μA）=-0.1925 C（μM）+1.0504（15μM-1500μM,R²=0.996）和I_p（μA）=-0.2137 C（μM）-0.5614（5μM-500μM,R²=0.993）,the lowest detection limit is 0.025μM,0.056μM,respectively and 0.051μM（S/N=3）.In addition,the sensor showed good interference resistance,storage stability（93.02%,85.67%and 92.62%current retention after 14 days,respectively）and reproducibility.The method showed a deviation of 5.41%from the HPLC method and was successfully applied to the determination of phenolic antioxidants in real samples.