Determination of Total Free Alkalinity in Soaps

The sum of free caustic alkali and free carbonate alkali contents is called Total Free Alkali. Determination of Total Free Alkalinity performed within the scope of ISO 684 standard is expressed as percent by mass of sodium hydroxide (NaOH) for sodium soaps or potassium hydroxide (KOH) for potassium soaps.

ISO 684 standard test process is not applicable if it contains various additives that are generally decomposed by sulfuric acid, color agents interfere with the phenolphthalein endpoint.

The test process steps can be roughly listed as follows.

• Soap is dissolved in an ethanolic solution,
• Free alkali is neutralized with a known excess sulfuric acid solution,
• Excess acid is titrated with ethanolic potassium hydroxide solution.

ISO 684: Analysis of soaps - Determination of total free alkali