Precipitation Issue in BHA Toner Formulation
Question
I have a question about a BHA Toner formulation I recently mixed. The formula is as follows:
Ingredients:
- Complex Salicylic Acid (Powder, Water-Soluble) 5%
- Pure-Succinic™ (Succinic Acid, High-Purity) 2%
- EDTA 0.2%
- Water Remaining amount
Procedure:
- Weigh ingredients 2 and 3, add to water, and stir until clear solution is formed. (This step had no issues; 2 and 3 dissolved easily in water.)
- Weigh ingredient 1 and add to water. Complex Salicylic Acid (Powder, Water-Soluble) precipitated immediately.
Questions:
- Why did Complex Salicylic Acid (Powder, Water-Soluble) precipitate?
This is despite the website stating it is water-soluble Salicylic Acid and not mentioning it should not be used with Pure-Succinic™ or EDTA. - Do I need to discard the BHA Toner where Salicylic Acid precipitated?
I am concerned that the toner will not be effective in dissolving clogged pores.
Thank you in advance for your answer.
Answer
Hello, I understand you encountered precipitation when mixing Complex Salicylic Acid with Succinic Acid, EDTA, and water.
Here are the answers to your questions:
1. Why did Complex Salicylic Acid (Powder, Water-Soluble) precipitate?
The most likely reason is that adding Pure-Succinic™ (Succinic Acid), which is an acid, lowered the pH of the solution.
While Complex Salicylic Acid is stated to be water-soluble, the solubility of Salicylic Acid is highly dependent on pH. In more acidic conditions, Salicylic Acid tends to convert to its less soluble free acid form, causing precipitation. The "water-soluble" claim for Complex Salicylic Acid usually implies good solubility within a specific pH range, which might be higher than the pH resulting from adding another acid like Succinic Acid at 2% concentration. Mixing two acidic ingredients in water can lower the pH to a point where the Salicylic Acid in the complex can no longer remain dissolved.
2. Do I need to discard the BHA Toner where Salicylic Acid precipitated?
Yes, it is necessary to discard this toner.
When Salicylic Acid precipitates, it is no longer properly dissolved or dispersed in the solution. This means it cannot effectively penetrate the skin to work on clogged pores. The toner will not have the intended efficacy. Using a product with precipitated ingredients can lead to inconsistent results or lack of effectiveness.
When combining multiple acidic ingredients, it is important to consider the final pH and the solubility requirements of each ingredient at that pH.
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