Evaluation Of The Oxidation Stability Of Vegetable Oils By Carbon-based Materials Modified Electrodes

Electrochemical analysis has become one of the hotspots in the field of analysis and detection because of its high sensitivity,convenience,and accuracy.In this dissertation,the reduction of oxidized graphene modified glassy carbon electrode?rGO/GCE?,plane reference electrodes,and screen-printing electrodes modified with nano-Prussian blue graphene oxide and lithium bis-?trifluoromethanesulfonyl?imide?PBNPs/rGO/Li TFSI/SPE?were prepared.Compared with the national standard colorimetric method,the AC impedance method and differential pulse voltammetry were used to measure the vegetable oils with different degrees of oxidation.The results showed that the established electrochemical method could conveniently and accurately detect the oxidation degree of vegetable oils.The main research contents and results are as follows:1.Preparation of reduced graphene oxide modified glassy carbon electrode and its application in the system of aqueous medium for the determination of oxidation induction time of vegetable oilsFirstly,graphene oxide and rGO/GCE were prepared,and the effects of the thickness of rGO film on the characteristics of the electrode were studied.The results showed that the rGO/GCE with 50 cycles of CV had the best performance.Secondly,an aqueous medium measurement system for the the determination of oxidation induction time of vegetable oils was established,which includes an oil-water mixing system,an oil-water separation system,and a measurement system.Furthermore,the influences of the aqueous mediums,oil-water volume ratios,and oil-water mixing degrees on the measurement results were studied investigated.The results showed that the measurement sensitivity was higher in the aqueous medium system with oil-water volume ratio of 1:1,copper wire length of 40 cm and pH 7.0 phosphate buffer solution.Lastly,the oxidation stability and the oxidation induction timeat different temperaturesof 6vegetable oils were measured with the AC impedance method and the national standard colorimetric method.The results indicated that the oxidation stability of those 6 vegetable oils from high to low were as follows:soybean oil,olive oil,avocado oil,rice bran oil,sunflower oil,almond oil.2.Study on planar solid reference electrode with nano-silver/reduced graphene oxide?AgNPs/rGO?composites as reinforcing materialsThe planar solid reference electrode was connstructed with the Ag/AgCl as the substrate,polyvinyl chloride?PVC?film doped with KCl and AgCl as the protective film,and the AgNPs/rGO composite as the reinforcing materials.The potential stability and other properties of the preparedplanar solid reference electrode were investigated.The results discovered that the prepared reference electrode had good potential stability in the concentration of 1×10^-31mol/L of inorganic salt solutions,such as Na₂CO₃,KCl,NaHCO₃,NaCl,KBr,the change of potential is 1.50 mV/dec,in the solution of pH 3¹1,the change of potential is 0.13 mV/dec,and in 1 mol/L KCl solution at 10⁵0°C,the change of potential is 0.30 mV/?5??,respectively.In addition,the planar solid reference electrode could still be used for 10 days soaked in 1 mol/L KCl solution,and its shelf life in a refrigerator at 4°C was at least 6 months.3.Preparation and application of screen printing electrodes modified with nano-Prussian Blue,reduced-graphene oxide and Lithium Bis-?trifluoromethanesulfonyl?imideNano-Prussian Blue?PBNPs?and PBNPs/rGO/LiTFSI/SPE were prepared,and the ratio of PBNPs,rGO,LiTFSI to conductive carbon paste was investigated.The results revealed that the electrochemical performance of the prepared electrode was the best when the mass ratio of conductive carbon paste,rGO,LiTFSI and PBNPs was 25:5:1:2.The results of the study on the enhancement of LiTFSI showed that the peak current was increased from 82%to 96 before and after the addition of LiTFSI when 100 cycles of CV was conducted.The prepared electrode was used as working electrode of SPE.The almond oil,rice bran oil,avocado oil and soybean oil were testedby differential pulse voltammetry at 70?,80?,and 90?,respectively.It was found that there was a linear relationship and the peroxide value?POV?.4.Establishment and analysis of shelf life model of vegetable oilBased on the measurement data obtained from the preceding research,the kinetic analysis of the oxidation process of vegetable oils at 5 different temperatureswas carried out by using impedance and POV as indexes,respectively.The oxidation rates and activation energies of different vegetable oils were obtained.The shelf life model of the vegetable oil was established,t=a×e^b?T,and it was verified by experiments.The results showed that the constructed shelf life model of vegetable oil was reliable and practical.