Study On The Electrochemical Process Of Raw Milk Doped With Urea And Sodium Chloride And Its Application

In this paper,urea and sodium chloride were used as the research object in raw milk.Electrochemical cyclic voltammetry and electrochemical analysis methods were used to study the safety and quality of raw milk.Besides,tested technology stability and repeatability of the method.In addition,for the detection items of several common adulterants,utilized the detection method of this article to design an electrochemical detection system of doping raw milk.Thus,it's easier to achieve the comprehensive identification of raw milk doping.The main findings are as follows:Electrochemical cyclic voltammetry was used to study the electrochemical response characteristics of urea and its adulterant into raw milk at the gold disk electrode,and the electrode interface information was characterized.The results showed that when the scanning potential ranged from 0 to 1.4 V and the scan rate was from 1 to 25 mV/s,the response characteristic of urea on the gold electrode was a single peak of reduction reaction,and the peak potential decreased linearly with the increasing of the scanning speed and concentration.On the other hand,the peak current value was linear with?^1/2(I_pc??A?=5.7410?^1/2-0.0770,R²=0.997).Therefore,the reduction reaction was controlled by diffusion,and the diffusion rate was much greater than the chemical reaction rate.The urea product could not stay on the surface of the electrode,so the urea electrode process was irreversible.The calculated number of the reaction's electron and protons were both 1,switching coefficient???was 0.558,and the electrochemical rate constant?k_s?was 0.4320±0.0001 s^-1.After mixing the urea into raw milk,the trichloroacetic acid was added to the doped milk,and blended.Clear liquid was obtained by centrifugation that removed the fat and protein.After the clear liquid was tested,it can be seen that,when the concentration of urea mixture was 0.3².5 mol/L,urea's concentration had a linear relationship with the peak current value(I_pc??A?=7.7847+3.3098 C?mol/L?,R²=0.994).The reduction of urea occurred on the surface of the gold electrode,and the peak potential showed a slight negative shift with increasing concentration.This method's detectability to urea was 0.0384 mol/L.The electrochemical characteristics of the silver electrode in the solution containing chloride ions was detected and the electrochemical process of the electrode interface was analyzed.The results showed that,when the scanning potential ranged from–0.65 to 0.4 V,the scanning speed was 0.01 to 0.5 V/s,redox reaction of the silver electrode occurred in the solution containing 0.02 mol/L chloride ions,and the peak current value showed a linear relationship with the scan rate(I_pc??A?=81.37?+188.53,R²=0.994;I_pa??A?=–23.64?–81.31,R²=0.990).Thus the electrode process was a quasi-reversible process controlled by reaction kinetics,and the number of electrons participating in the reaction was approximately 1.In addition,the redox peak current value increased with the increasing of the chloride ions concentration in the solution.The oxidation peak potential appeared near 0.145 V,and the reduction peak potential had a negative shift,indicating that when the chloride ions concentration was higher,it's hard to occur reduction reaction for the silver electrode.After mixing different concentrations of sodium chloride into raw milk.Clear liquid was obtained by centrifugation that removed the fat and protein.After the clear liquid was tested,it can be seen that,when the doping concentration was 0 to 0.18mol/L,the oxidation peak potential appeared near 0.176 V,and the reduction peak potential had a negative shift?–0.040 to–0.216 V?showed a linear relationship with sodium chloride concentration(I_pa??A?=–3729.5 C?mol/L?–90.4,R²=0.990,I_pc??A?=6068.3 C?mol/L?+276.7,R²=0.990).This method's detectability to chloride ions in the milk sample was 0.001 mol/L.By measuring the recovery rate of raw milk and its adulterated milk,and t-test with the common method,it can be seen that the average recovery rate of urea in the sample was 103.7%,and the t value was 0.609,which was less than the critical value of 2.776,and P value 0.576 was greater than 0.05.Besides,the average recovery rate of chlorine ions in the sample was 102.58%,and the t value was 0.345,less than the critical value of 2.776,and the P value was 0.747 more than 0.05.It showed that the electrochemical cyclic voltammetry detection technology in this paper had good stability and reproducibility,and there was no obvious difference with the commonly used detection technology.It can be better applied to the industrial line.In addition,five working electrodes,which can specifically identify urea,sodium chloride,melamine,reconstituted milk,and rancid milk,had been designed and integrated to a set of sensor arrays,such as gold disk electrode,silver disk electrode,palladium electrode,titanium electrode,and tungsten electrode.A centralized control device was designed between the sensor array and the constant potential/constant current,in order to realize the control of the working state of the single research electrode of the sensor.