I. Preface
The quality of edible oil is closely related to human health. Acid value and peroxide value are important indicators for evaluating the quality of edible oil. Acid value reflects the content of free fatty acids in edible oil, while peroxide value indicates the degree of oxidation and rancidity of the oil. Accurate determination of these two indicators is of vital importance for ensuring the quality and safety of edible oil. The JH-T9 fully automatic potentiometric titrator of Shanghai Jiahang Instrument & Meter Co., Ltd. provides an efficient and accurate solution for the determination of acid value and peroxide value of edible oil with its advanced technology and stable performance.

Ii. Detection Principle
(1) Principle of Acid Value Determination
Acid value refers to the milligram number of potassium hydroxide (KOH) required to neutralize the free fatty acids in 1 gram of oil. Its determination is based on the principle of acid-base neutralization reaction. Free fatty acids in edible oil undergo neutralization reaction with potassium hydroxide standard solution, and the reaction formula is: RCOOH + KOH → RCOOK + H?O. During the titration process, as the potassium hydroxide standard solution is added, the pH value of the solution will change. The JH-T9 fully automatic potentiometric titrator monitors the pH value changes of the solution in real time through the pH non-aqueous electrode. When the titration endpoint is reached, the pH value will show a sudden jump. The instrument automatically recognizes this change and records the volume of the consumed potassium hydroxide standard solution, and then calculates the acid value.

(II) Principle of Peroxide Value Determination
The peroxide value is an indicator indicating the degree of oxidation of oils, fats and fatty acids, etc. It is measured by the content of active oxygen in 1 kilogram of sample (expressed in millimoles of peroxides). In this experiment, the peroxide value was determined by the iodometric method. Peroxides in edible oil react with potassium iodide under acidic conditions to form free iodine. The reaction equation is: ROOH + 2KI + H?SO? → I? + ROH + K?SO? + H?O. The generated free iodine is titrated with sodium thiosulfate standard solution as follows: 2Na?S?O? + I? → Na?S?O? + 2NaI. The JH-T9 fully automatic potentiometric titrator uses a composite platinum electrode to monitor the changes in the solution potential during the titration process. When the titration endpoint is reached, the potential undergoes a sudden jump. The instrument records the volume of the consumed sodium thiosulfate standard solution, thereby calculating the peroxide value.

Iii. Instruments and Reagents
(1) Instruments
JH-T9 Fully automatic potentiometric Titrator: Produced by Shanghai Jiahang Instrument & Meter Co., LTD., it features a high-precision titration system and a sensitive electrode detection system, enabling automated titration and data processing.
Analytical balance: With an accuracy of 0.0001g, it is used for accurately weighing edible oil samples and reagents.
Composite non-aqueous pH electrode: It is used to monitor the changes in solution pH value during acid value determination.
Composite platinum electrode: Used for monitoring the potential changes of the solution during the determination of peroxide value.
Titration cup: It is used for holding sample solutions and conducting titration reactions.
Volumetric flasks, pipettes and other glassware: used for preparing standard solutions and transferring reagents.
(II) Reagents
Potassium hydroxide standard titration solution (0.1mol/L) : Accurately weigh a certain amount of potassium hydroxide, dissolve it in water free of carbon dioxide and make up to the required volume, then calibrate it according to the standard method.
Isopropyl alcohol-ether mixed solution: Isopropyl alcohol and ether are mixed in a certain proportion and used to dissolve edible oil samples.
Sodium thiosulfate standard titration solution (0.01mol/L) : Weigh an appropriate amount of sodium thiosulfate, dissolve it in freshly boiled and cooled distilled water, add a small amount of sodium carbonate, make up to volume, and let it stand for a period of time for calibration.
Potassium iodide solution (150g/L) : Weigh 150g of potassium iodide, dissolve it in water and dilute it to 1000mL.
Sulfuric acid solution (20%) : Measure a certain volume of concentrated sulfuric acid and slowly add it to an appropriate amount of water. After cooling, dilute it to the required concentration.
Soluble starch indicator solution (10g/L) : Weigh 1g of soluble starch, add a small amount of water to form a paste, then add 100mL of boiling water, boil for a few minutes, and use after cooling.
Iv. Experimental Procedures
(1) Steps for determining acid value
Sample preparation: Accurately weigh an appropriate amount (generally 3-5g) of edible oil sample, accurate to 0.0001g, and place it in a titration cup.
Solution preparation: Add 60mL of the isopropanol-ether mixed solution to the titration cup, stir evenly to ensure the sample is completely dissolved.
Instrument calibration: Turn on the JH-T9 fully automatic potentiometric titrator, preheat for a period of time, and then calibrate the pH non-aqueous electrode with standard buffer solution to ensure the accuracy of electrode measurement.
Titration operation: Insert the calibrated pH non-aqueous electrode into the titration cup and start the titration program. Titration was carried out using potassium hydroxide standard titration solution (0.1mol/L). The instrument automatically recorded the pH value changes and the volume of potassium hydroxide standard solution consumed during the titration process until the titration endpoint (pH value jump point) was reached.
Result calculation: Based on the volume (V?), concentration (C?) of the potassium hydroxide standard solution consumed during titration and the mass (m) of the sample, calculate the acid valence (AV) according to the formula:
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Among them, 56.11 is the molar mass of potassium hydroxide (g/mol).

(II) Steps for peroxide value determination
Sample preparation: Accurately weigh an appropriate amount (generally 2-3g) of edible oil sample, accurate to 0.0001g, and place it in a dry iodine volumetric flask.
Reagent addition: Add 30mL of the chloroform - glacial acetic acid mixture to the iodine flask, and gently shake to dissolve the sample. Then add 1.00mL of potassium iodide solution (150g/L), tightly stopper the bottle, gently shake well and let it stand in the dark for 5 minutes.
Reaction termination and dilution: After the reaction is completed, immediately add 100mL of water, shake well, and transfer the solution to a titration cup.
Instrument calibration: The composite platinum electrode of the JH-T9 fully automatic potentiometric titrator can be calibrated using a standard solution with a known potential.
Titration operation: Insert the calibrated composite platinum electrode into the titration cup and titrate with sodium thiosulfate standard titration solution (0.01mol/L). During the titration process, the color of the solution gradually lightens. When the solution turns light yellow, add 1mL of soluble starch indicator solution and continue titration until the blue color just disappears, which is the endpoint of the titration. The instrument automatically records the volume (V?) of the consumed sodium thiosulfate standard solution.
Blank test: Conduct the blank test simultaneously. Except for not adding the sample, all other operation steps are the same as those for sample determination. Record the volume (V?) of the sodium thiosulfate standard solution consumed in the blank test.
Result calculation: Based on the volume (V?, V?), concentration (C?) of the sodium thiosulfate standard solution consumed during titration and the mass (m) of the sample, the peroxide value (POV) is calculated according to the formula:
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The unit is mmol/kg.

V. Instrument Features and Advantages
(1) High-precision titration system
The JH-T9 fully automatic potentiometric titrator adopts advanced burette drive technology, which can precisely control the addition amount of titrant. The titration accuracy can reach ±0.001mL, effectively reducing titration errors and ensuring the accuracy of the determination results.

(2) Intelligent electrode Detection
The equipped composite non-aqueous pH electrode and composite platinum electrode feature high sensitivity and stability, enabling rapid and accurate detection of potential or pH value changes in the solution, and providing real-time feedback on the reaction during the titration process, making the determination of the titration endpoint more precise.

(3) Automated operation
The instrument is equipped with a highly automated function. From the initiation of the titration process, the addition of titrant, the determination of the endpoint to the recording and processing of data, all can be automatically completed by the instrument. The operator only needs to carry out simple sample preparation and parameter setting, which greatly improves work efficiency and reduces the influence of human factors on the experimental results.

(4) Data Processing and Storage
It can automatically store a large amount of experimental data, facilitating subsequent query and analysis. Meanwhile, the instrument can output experimental reports in standard format, including detailed information such as sample details, measurement results, and titration curves, meeting the requirements of laboratory data management and quality control.

(V) Easy to operate
The operation interface of the instrument is simple and intuitive, featuring a color touch screen design. Users can easily complete various Settings and input operation instructions through touch operation. Even those who are using it for the first time can quickly get started after a simple training.

Vi. Precautions
(1) Reagent preparation and storage
Potassium hydroxide standard titration solutions and sodium thiosulfate standard titration solutions should be prepared and calibrated in accordance with standard methods and properly stored. During the storage process, it is necessary to prevent the solution from absorbing carbon dioxide and moisture from the air to avoid affecting the solution concentration.
Potassium iodide solution is prone to oxidation and should be prepared as needed. If the prepared potassium iodide solution turns yellow, it indicates that it has been partially oxidized and cannot be used any longer.
Reagents such as isopropanol-ether mixed solution and sulfuric acid solution are volatile and corrosive. They should be prepared and used in a well-ventilated environment, and proper protective measures should be taken.
(II) Electrode Maintenance
Before using the composite non-aqueous pH electrode and the composite platinum electrode, it is necessary to carefully check whether the electrode membrane is intact and whether there is any damage or contamination. If the electrode membrane is contaminated, it should be cleaned and activated in accordance with the requirements of the electrode manual.
After use, the electrode should be cleaned thoroughly and soaked in the corresponding protective solution to maintain its performance and service life. For instance, the pH non-hydro electrode should be immersed in an ethanol solution containing lithium salts after use, and the composite platinum electrode can be immersed in distilled water after use.
Calibrate the electrodes regularly to ensure the accuracy of electrode measurements. During the calibration process, if it is found that the electrode response is slow or the calibration result deviates significantly, the electrode should be considered for replacement.
(III) Sample Processing
When weighing edible oil samples, it is necessary to ensure that the samples are representative to avoid taking the upper clear liquid or the lower sediment part. For edible oil with high viscosity, it can be appropriately heated to increase its fluidity, but the heating temperature should not be too high to avoid affecting the properties of the sample.
In the determination of peroxide value, when the sample reacts with potassium iodide, it should be placed in the dark to avoid light accelerating the oxidation of potassium iodide and affecting the determination results. Meanwhile, the reaction time should be strictly controlled within 5 minutes. Either too long or too short will lead to inaccurate results.
(4) Experimental Environment
The experiment should be conducted in an environment with relatively stable temperature and humidity to avoid interference from environmental factors on the experimental results. Temperature changes may affect the volume of the solution and the performance of the electrode. When the humidity is high, it may cause the reagent to absorb moisture and deteriorate.

Vii. Conclusion
The JH-T9 fully automatic potentiometric titrator of Shanghai Jiahang Instrument & Meter Co., Ltd. demonstrates outstanding performance in the determination of acid value and peroxide value of edible oil. This instrument is easy to operate, highly accurate in measurement and has a high degree of automation. It can effectively meet the needs of edible oil production enterprises, quality inspection institutions, etc. for edible oil quality inspection. By strictly following the experimental procedures and paying attention to all precautions, reliable determination results can be obtained, providing strong technical support for ensuring the quality and safety of edible oil. .