The peroxide produced in the process of oil oxidation reacts with potassium iodide to generate free iodine, and the content is calculated by titration with sodium thiosulfate solution. 4.2.2 Reagent 4.2.2. 1 saturated potassium iodide solution: weigh 14g potassium iodide, add 10mL water to dissolve it, slightly heat it if necessary, and store it in a brown bottle after cooling. 4.2.2.2 chloroform-glacial acetic acid mixture: measure 40mL chloroform, add 60mL glacial acetic acid and mix well. 4.2.2.3 sodium thiosulfate standard titration solution [c (Na2S2O3) = 0.002mol/L]. I can use 0.005 mol. ) 4.2.2.4 Starch indicator (10g/L): Weigh 0.5g of soluble starch, add a little water to make paste, pour it into 50mL boiling water, mix well and boil. Ready to use. 4.2.3 Analysis Step Weigh 2.00 ~ 3.00 g of evenly mixed (filtered if necessary) samples, put them in a 250mL iodine bottle, and add 30mL of chloroform-glacial acetic acid mixed solution to completely dissolve the samples. Add 1.00mL saturated potassium iodide solution, tightly plug the bottle cap, gently shake it for 0.5min, and then place it in the dark for 3min. Take out the added 100mL water, shake it well, and titrate it with sodium thiosulfate standard titration solution (0.002mol/L) immediately. When it turns light yellow, add 1mL starch indicator, and continue titration until the blue color disappears. Take equal amounts of chloroform-glacial acetic acid solution, potassium iodide solution and water, and do reagent blank test in the same way. (Blank test must be done for each sample) Calculate 4.2.4 in the formula: x2-peroxide value of the sample, g/100g; X3-peroxide value of the sample, meq/kg；; ; V2—— the volume of standard titration solution of sodium thiosulfate consumed by the sample, ml; V3—— the volume of standard titration solution of sodium thiosulfate consumed in reagent blank, ml; C2—— concentration of standard titration solution of sodium thiosulfate, mol/l; M2—— sample mass, g; 0. 1269—— the mass of iodine equivalent to 1.00mL sodium thiosulfate standard titration solution [c(Na2S2O3)= 1.000mol/L], g; ; 78.8—— Conversion coefficient. Result Description: Report two significant figures of arithmetic mean. 4.2.5 The relative difference of allowable difference is ≤ 10%.