Adjusting pH of Glycolic Acid Solution

Regarding your questions about adjusting the pH of your 10% glycolic acid solution:

1. Which substance should be used to adjust the pH?

   • Triethanolamine is recommended for increasing the pH of acidic solutions like glycolic acid. It is a concentrated alkaline substance, so it should be added drop by drop while continuously measuring the pH. Typically, a concentration of less than 1% is sufficient.

2. Will raising the pH affect the efficacy of AHA?

   • The efficacy of AHA will remain good as long as the pH is not raised above 3.5. Raising the pH significantly higher than this range (3.5-4.5) can reduce its exfoliating effectiveness.

3. Regarding the use of Sodium Citrate:

   • You observed that a large amount of Sodium Citrate was needed to increase the pH. This is because Sodium Citrate is acidic and acts more as a buffer to stabilize pH rather than effectively raising it from a highly acidic point like 2.10 to the desired range of 3.5-4.5.
   • Will it affect the skin? Sodium Citrate itself does not typically cause issues for the skin when used within recommended cosmetic limits. However, using a very large amount to try and force a pH change might introduce other formulation stability issues or unintended effects, although the staff indicated it wouldn't affect the skin if all ingredients are within specifications.
   • Can this substance be used? Sodium Citrate is not suitable for raising the pH of a highly acidic solution. It is better suited for use as a buffering agent to help maintain a desired pH within the 3.5-4.5 range once it has been adjusted with an alkaline substance like Triethanolamine.

In summary, use Triethanolamine to carefully raise the pH to the 3.5-4.5 range, ensuring it does not exceed 3.5 to maintain optimal AHA efficacy. Sodium Citrate is not effective for raising pH and is better used as a buffer.