Acid Value
Acidity is frequently expressed as the Acid Value, which is the number of mg of potassium hydroxide required to neutralize the free acids in 1.0 g of the substance.
USP 401
The acidity of fats and fixed oils in USP may be expressed as the number of mL of 0.1 N alkali required to neutralize the free acids in 10.0 g of substance.
Method II
Prepare 125 mL of a solvent mixture consisting of equal volumes of isopropyl alcohol and toluene. Before use, add 2 mL of a 1% solution of phenolphthalein in isopropyl alcohol to the 125 mL mixture and neutralize with alkali to a faint but permanent pink color. Weigh accurately the appropriate amount of well-mixed liquid sample indicate in the table below, and dissolve it in the neutralized solvent mixture. If the test specimen does not dissolve in the solvent, connect the flask with a suitable condenser and warm slowly, with frequent shaking, until the specimen dissolves. Shake vigorously while titrating with 0.1 N potassium hydroxide VS or 0.1 N sodium hydroxide VS to the first permanent of the same intensity as that of the neutralized solvent, before mixing with sample. Calculate Acid value by the formula:
56.11V X N/W
| Acid Value | Sample Weight (g) |
|---|---|
| 0-1 | 20 |
| 1-4 | 10 |
| 4-15 | 2.5 |
| 15-74.9 | 0.5 |
| ≥75.0 | 0.1 |
Referencia
- Pharmacopedia/National Formulary. US. Vol. 1, 151