Application Of Electrochemical Sensor To Detect Nitrite In Food

Nitrite is a common food additive that has antiseptic properties because it inhibits the growth of Clostridium botulinum.It can also be used as a colorant to react with myoglobin in meat to preserve meat and other products color,aroma and taste.However,nitrite is very toxic.Excessive intake will cause toxic reactions,abdominal pain,vomiting and other adverse symptoms,and even damage the blood oxygen supply function.If ingested in excess,it will cause harm to the human body,and it also has a strong risk of cancer.Therefore,in the food processing industry,it is necessary to strictly control the amount of nitrite added.Sodium nitrite is mainly used in my country.With people's attention to food safety,the detection of nitrite in food has become an indispensable link.In order to control food safety,it is necessary to detect the content of nitrite in food.At present,there are many methods for the determination of nitrite reported at home and abroad,such as UV-visible spectrophotometry,catalytic luminescence photometry,oscillometric polarography,gas chromatography and so on.The commonly used methods for the determination of nitrite are colorimetry and polarography.Although they have the advantages of rapidity,simplicity,and wide applicability,they also have shortcomings such as low precision and low selectivity.In recent years,electrochemical sensors have become the main means of nitrite determination due to their high sensitivity,fast detection,and low cost.Metal-organic frameworks(MOFs)are a class of hybrid inorganic-organic covalent nanocrystalline materials with high porosity,large specific surface area,tunable pore size,and diverse crystal shapes.It can meet the needs of electrochemical sensors.However,there are not many types of single-metal MOFs used for modified electrodes,and most of the MOFs have poor conductivity and low redox activity.The preparation method of MOFs-modified electrodes needs to be improved.Therefore,improving the preparation method of modified electrodes to improve the conductivity of MOFs is a major research direction.It is of great significance to develop the application of MOFs in electrochemical sensors,construct new electrochemical sensors of MOFs and MOFs derivatives,and establish rapid detection methods for analytes in the fields of medicine,biology,environment,and food.In this study,the electrocatalytic effect of several metal ions synthesized MOFs on sodium nitrite was investigated.The optimal metal sites were screened,and a composite material was developed using hydrothermal synthesis and electrochemical methods which was deposited onto glassy carbon electrode(GCE)surface,which realizes the detection of nitrite.The specific research contents mainly include:(1)A method for electrochemical detection of nitrite based on metal MOFs was established.Metal MOFs were deposited in situ onto GCE surface by cathodic reduction,and their structures and chemical properties were investigated.The oxidation peak current,deposition voltage,deposition time and other conditions of single metal mixed with different molar ratios were mainly investigated.The best metal site Fe was selected to fabricate MOF material modified GCE.(2)Graphene is a carbon material with a sheet-like structure,which has good electrical conductivity and stability.Due to the introduction of hydrophilic oxygen-containing active groups,graphene oxide has the characteristics of surface activity,wettability,dispersibility and compatibility.The reduced graphene oxide(r GO)combines the advantages of both.Based on the experimental conclusions in the previous chapter,the r GO/Fe-MOFs composite material was studied in combination of r GO with Fe-MOFs.After deposition by the I-t method,the optimal conditions for the detection of sodium nitrite by the composite material were obtained by analyzing the differential pulse curve.The influencing factors of its standing time,solution p H and nitrite concentration were optimized.Under the optimal experimental conditions,the electrochemical signal gradually decreased with the decrease of the nitrite concentration,and there was a linear correlation between the oxidation peak current and the concentration with a regression equation of I_pa(?A)=0.11C(?M)+2.48(R~2=0.999).The detection limit was obtained as low as0.7?M.In the detection of actual samples of raw milk,a higher recovery was obtained.