Formulation Advice for AHA Gel

Regarding your experiment with the AHA gel formulation using 10% Glycolic acid and 0.6% Hydroxyethyl cellulose (HEC), and adjusting the pH to 3.6:

Triethylamine (TEA) Usage

Using 8-9% Triethylamine (TEA) to adjust the pH of a 10% Glycolic acid solution to 3.6 is considered a relatively high amount. Based on general recommendations and regulations for similar pH adjusters like Triethanolamine, usage rates are often suggested not to exceed 5%, and for high purity grades, typically not more than 2.5% in cosmetic formulations. The exact amount needed will depend on the initial acidity of your specific Glycolic acid source and the desired final pH, but 8-9% is on the higher end of typical usage ranges.

Foaming with Sodium Bicarbonate

The foaming that occurs when adding Sodium Bicarbonate to the Glycolic acid solution is a normal chemical reaction. It is the reaction between the acid (Glycolic acid) and the base (Sodium Bicarbonate) producing carbon dioxide gas, which causes the bubbles. This reaction does not reduce the effectiveness of the Glycolic acid that remains in the solution at your target pH. The Sodium Bicarbonate works by neutralizing some of the acid to reach the desired pH level, and the foaming is simply a visible sign of this neutralization process.

Both Triethanolamine and Sodium Bicarbonate are effective pH adjusters for acidic formulations like those containing Glycolic acid. Sodium Bicarbonate is often recommended as an alternative to amines for pH adjustment in AHA/BHA formulas and can also be used as a neutralizer after using high-concentration acids on the skin.