Rapid measurement of the peroxide content of oxides in edible oils by UV-1100 spectrophotometry - Master's thesis - Dissertation

Rapid determination of the peroxide value of oxides in edible oil by spectrophotometry. Establishment of the standard curve of edible oils. Precipitation Instrument Co., Ltd. Preface The toxic substances such as peroxides produced by metamorphic oils convert hemoglobin 2 valence iron into hemoglobin 3 valent iron. The toxic effect causes hemoglobin to lose its oxygen-carrying function, causing hypoxia in the body, and mucous membranes and purpura on the skin. The oxide of the rancid substance directly destroys the important enzymes such as succinate oxidase and cytochrome oxidase in the enzyme system, interferes with the tricarboxylate cycle and oxidative phosphorylation in the cell, and causes disorder of energy metabolism in the cell. Intracellular asphyxia causes acute respiratory and circulatory failure in patients. The oxidation depth of the grease, that is, the peroxide value of the grease oxide, directly affects the quality and performance of the fatliquor. Therefore, it is important to determine the peroxide value of the oil oxide to determine the oxidation depth of the grease. The classical method currently used is the iodometric method, which is cumbersome to operate, has a large influence on human factors, and is harmful to the environment and operators. In this experiment, the peroxide value of edible oil was determined by spectrophotometry. The acid value of oil was tested to evaluate the quality of oil and fat, and to judge the quality change during oil storage. Let us eat more confidence in oil food. 1. Experimental purpose The peroxide of the edible oil reacts with the KI solution in the chloroform-glacial acetic acid medium to form I2, and the resulting I2 reacts with the blue color of the starch, and the absorbance A value of the edible oil is measured by a spectrophotometer. According to the standard solution curve of I2, the concentration c of the consumption I2 in the reaction is determined, and the peroxide value of the peroxide in the oil and fat is calculated according to the concentration of the consumed I2, thereby evaluating the quality of the oil and the quality of the oil during storage. 2. Experimental principle The peroxide of the edible oil reacted with the KI solution to form I2 in the chloroform-glacial acetic acid medium, and the resulting I2 reacted with the blue color of the starch, and the absorbance A value of the edible oil was measured by a spectrophotometer. R-OOH+2KI+2H^+=I2+R-OH+H2+2K^ titrate c=0.1mol/LI2 solution with c=0.1mol/L Na2S203 standard solution, and prepare standard solution I2+2Na2S2O3=Na2S4O6+2NaI The standard solution of c=0.1 mol/LI2 was prepared to be 0.0002 mol/L, 0.0004 mol/L, 0.001 mol/L, 0.002 mol/L, 0.003 mol/L, 0.004 mol/L, 0.006 mol/L and 0.008 mol/ L, the absorbance A value is measured by a spectrophotometer at a wavelength of 535 nm, the solution concentration is plotted on the abscissa with I2, the absorbance is plotted on the ordinate, the working curve of the standard solution of I2 is plotted, and then the edible oil peroxide and KI are used. The absorbance value A of I2 produced by the solution reaction determines the I2 concentration produced by the reaction in the working curve, and substitutes the formula to determine the peroxide value of the peroxide in the oil. 3. Experimental equipment beaker (50mL, 250mL, 500mL), electric drying oven, iodine measuring bottle (250mL), measuring cylinder (10mL), brown acid burette (25.00mL), electronic balance (0.01g), volumetric flask (100mL, 250mL, 500mL), pipette (25.00mL), with colorimetric tube (50mL), pipette (1.00mL), brown reagent bottle (500mL), electric furnace, test tube rack, glass rod, iron frame, ear wash ball. US Instruments V-1100 Spectrophotometer 4, Experimental Materials and Reagents 4.1 Solution Preparation (1) A glacial acetic acid mixed solvent (40:60) (2) 1% saturated starch solution indicator (3) 10% potassium iodide solution ( c=8.43mol/L or 1400g/L) (4)c=0.1mol/LI2 standard solution 4.2 Experimental material potassium iodide (solid), c=0.1mol/L Na2S203 standard solution, glacial acetic acid, 10g/L starch solution, edible Oil, water, 6mol/L HCl, I2 (AR solid), K2Cr2O7 (AR, 105-110 drying for 1 hour) 5. Operation procedure 5.10% potassium iodide solution preparation Analytical balance Weigh 10.00g potassium iodide solid in 50mL beaker Add appropriate amount of distilled water to dissolve, then transfer the dissolved potassium iodide into a 100mL volumetric flask, add distilled water to the mark line, cover the stopper, shake well, and place in a cool place for use. 5.2 One glacial acetic acid mixed solvent preparation Take 40mL in a beaker, then use 60mL measuring cylinder to take 60mL glacial acetic acid into a beaker and mix and set aside. Preparation and calibration of 5.3I2 quasi-solution 6.2.1I2 preparation: Weigh 6.5g of iodine in a beaker, then weigh 20gKI (three times with iodine weight of potassium iodide) and dissolve it into 500mL beaker with 50ml distilled water, then pour I2 In the KI solution, completely dissolve it, dilute with water to about 500 mL, add three drops of concentrated HCl, and finally pour the solution into a brown reagent bottle and store it in the dark. 6.2.2 I2 calibration: use a 25.00mL pipette to absorb c = 0.1mol / L Na2S203 standard solution, add 50mL of distilled water, then add 1mL% starch solution, with I2 droplets set to light blue, three times in parallel. Make a note of V(I2). Mass concentration of iodine element = (25.00 × c) / V where: c is the concentration of Na2S203 standard solution mol / L, V is the volume of iodine solution required for titration / mL 6.2.30.1mol / LI2 standard solution preparation: Pipette 10 mL of the calibrated I2 stock solution into a 200 mL volumetric flask and dilute to the mark with distilled water. 6.2.4 Drawing of the standard curve of the solution 6.3.1 respectively, 0.1mL, 0.2mL, 0.5mL, 1.0mL, 1.5mL, 2.0mL, 3.0mL, 4.0mL of the 0.1mol/LI2 standard solution were diluted to 50mL. It is formulated into an I2 standard solution of 0.0002 mol/L, 0.0004 mol/L, 0.001 mol/L, 0.002 mol/L, 0.003 mol/L, 0.004 mol/L, 0.006 mol/L and 0.008 mol/L. 6.3.2 Pipette 5mL of the above standard solution into the colorimetric tube, add 5mL of glacial acetic acid mixture, add 3 drops of 1% saturated starch solution indicator, cover and shake; then take another Pipette only 5 mL of distilled water and 5 mL of glacial acetic acid mixture, then add 3 drops of 1% saturated starch solution indicator, cover and shake well as a reference solution. 6.3.3 The above solution was separately aspirated with a plastic dropper, and the absorbance A of the solution after color development was measured with a spectrophotometer at a wavelength of 535 nm, and data was recorded. 6.3.4 Take the I2 standard solution mass concentration as the abscissa and the corresponding absorbance as the ordinate to draw the standard curve of the I2 standard solution. 6.5 Collection of edible oils In the market, bulk edible oils are purchased, and then the appropriate amount is taken out in a beaker, left to stand, and ready for use. 6.6 Determination of peroxide value of edible oil oxides 6.6.1 Weigh 0.20g of edible oil in an iodine measuring flask with an electronic analytical balance, draw 5mL of glacial acetic acid into the edible oil with a pipette, and measure 10mL of 10% potassium iodide by a measuring cylinder. The solution was poured into an iodine measuring flask, and then 3 drops of a 1% saturated starch solution indicator was added dropwise, and the stopper was capped, shaken well, and allowed to stand for 5 min. Another 5 mL of distilled water, 1% saturated starch solution indicator and 5 mL of glacial acetic acid mixture were used as reference solutions. 6.6.2 Dip an appropriate amount of the mixture into a cuvette with a plastic dropper, measure the absorbance at a wavelength of 535 nm with a spectrophotometer, and record the data.