pH of Oleic Acid (90%) and the relevance of Acid Value

The concept of pH (potential of Hydrogen) is defined for aqueous solutions, meaning solutions where water is the solvent.

Oleic Acid (90%) is a pure fatty acid in the form of an oil, which is an anhydrous (water-free) substance. Therefore, pure Oleic Acid does not have a measurable pH in the traditional sense.

Instead of pH, the standard quality control parameter used to measure the acidity of fatty acids like Oleic Acid is the Acid Value (or Acid Number).

• Acid Value: This value indicates the amount of free fatty acids present and is defined as the milligrams of potassium hydroxide (KOH) required to neutralize the free fatty acids in one gram of the sample. This is the parameter you would typically find on a COA for a fatty acid.

If Oleic Acid is dispersed in water (e.g., in a cosmetic emulsion), the carboxyl group (-COOH) will dissociate, making the resulting solution acidic. The pH of a cosmetic product containing Oleic Acid will depend entirely on the other ingredients in the formulation and the use of pH adjusters.