Issues with Vitamin C Serum Formulation: pH Adjustment, Stickiness, and Vitamin C/B3 Compatibility

Advice for Making Vitamin C Serum

Regarding the issues you're experiencing with adjusting pH using Triethanolamine (TEA) and the immediate yellowing when mixing Vitamin C and Vitamin B3, here is some advice:

pH Adjustment with Triethanolamine (TEA)

Needing to use Triethanolamine (TEA) up to 7% to achieve a pH of 3.6-3.7 for your 15% Vitamin C formula is unusually high. Generally, Triethanolamine (TEA) should not be used at more than 2.5% in cosmetic formulations according to product information, and using a high amount can indeed result in a sticky feeling as you observed.

Reasons why you might need such a high amount of Triethanolamine (TEA) could include:

• Very Low Initial pH: Before adding any TEA, you should measure the pH of your mixture. If it's much lower than expected, you might need to check the quality of the L-ascorbic acid you are using.
• Raw Material Quality: Even if the materials are new, other factors can affect the pH.

Alternative pH Adjusters:
Besides Triethanolamine (TEA), you can use other bases to adjust pH, such as Sodium Hydroxide or Potassium Hydroxide. These are stronger bases and must be handled with extreme caution. You should prepare a dilute solution (e.g., 10% or 20%) and add it drop by drop to your formula while continuously measuring the pH to avoid overshooting your target. Using a dilute solution makes it easier to control the pH change.

Mixing Vitamin C and Vitamin B3

The problem of immediate yellowing when mixing Vitamin C (L-ascorbic acid) with Vitamin B3 (Niacinamide) is due to the incompatibility of their optimal pH ranges for stability.

• Vitamin C (L-ascorbic acid): Is stable and effective at a low pH (around 2.5-3.5)
• Vitamin B3 (Niacinamide): Is stable at a higher pH (around 5-7)

When mixed directly in the same formula, the differing pH requirements cause both ingredients to degrade rapidly, often resulting in yellowing.

Solution:
As suggested in the forum thread, you can try to mitigate this by dissolving the Vitamin B3 (Niacinamide) in a small amount of water separately first. Then, carefully adjust the pH of the Vitamin B3 solution downwards slightly with a mild acid (like a drop of your Vitamin C solution or a citric acid solution) before combining it with your main Vitamin C serum. This helps reduce the pH difference upon mixing and minimizes the reaction that causes yellowing. However, achieving long-term stability for both vitamins in the same formula remains challenging.

Furthermore, using sterile water for irrigation instead of tap water was the correct step, as tap water contains minerals and impurities that can accelerate the degradation of Vitamin C, even with the addition of Disodium EDTA.

I hope this advice helps you improve your serum formulation.