What are the precautions for titration endpoint determination of acid value?
Precautions for Titration Endpoint Determination in Acid Value Testing
Endpoint Judgment Accuracy
Indicator Selection: Phenolphthalein is commonly used, with the endpoint appearing as a stable pink color lasting for at least 30 seconds. For samples with excessive color depth or unclear endpoints, thymolphthalein (blue endpoint) or reduced sample volume may be employed.
Background Interference: Observe the endpoint against a white background to minimize color interference.
Titration Operational Details
Titration Speed: Administer titrant slowly with continuous shaking to prevent localized excess and artificially high results.
Solvent Influence: Ethanol concentration must exceed 40% to prevent dissociation of potassium fatty acid salts. Ether-ethanol mixed solvents should be freshly prepared to avoid volatility or peroxidation interference.
Sample and Reagent Control
Sample Preparation: Solid fats must be uniformly melted; samples containing impurities require filtration to prevent endpoint interference.
Reagent Blank: Conduct parallel blank tests to exclude errors introduced by ether peroxides or moisture.
Instrument Calibration
Buret Calibration: Ensure graduated buret accuracy to avoid volumetric errors.
Standard Solution Verification: Regularly validate potassium hydroxide/sodium hydroxide concentrations to prevent result deviations.
Handling Special Cases
High Acid Value Samples: Reduce sample weight to improve titration precision.
Dark-Colored Oils: Increase solvent volume or switch to more sensitive indicators.
These measures collectively address critical factors in endpoint determination, ensuring the accuracy and reproducibility of test results.
The ST-13A automatic potentiometric titrator is designed in accordance with Method 2 (Cold Solvent Automatic Potentiometric Titration) of GB 5009.229-2016 Determination of Acid Value in Foods and GB 5009.227-2023 Determination of Peroxide Value in Foods, among other standards.
The instrument employs potentiometric titration to automatically determine the endpoint and calculate results. It is suitable for measuring acid values in various food samples, including edible oils, where acid value is a key indicator of oil quality. The titration system is built with imported corrosion-resistant components, ensuring high measurement accuracy and long service life.
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