-
Buffer solution
Hello,
i have a question please!
When the water is basic, for example (if we add sodium citrate to the water the water becomes around 7 or 9, right?) Will the solution that contains the citrate and water [buffer solution] affect the active ingredients that I will add to this solution later? For example, I want to make a salicylic serum and pH stability for salicylic acid is from 3-4,
is salicylic acid will be affected when added to a solution with a pH of 7 or 9 or buffer solution of sodium citrate?
Please I need your answer.
Thanks in advance.
-
6 Replies
-
Maybe I am wrong, but buffer solution to me is not just some base in water, but also a corresponding acid. E.g. citrate buffer is Sodium Citrate + Citric acid + Water.
Anyway when you add Salicylic acid to sodium citrate solution you get this:
Sodium Citrate + Water + Salicylic Acid -> Sodium Salicylate + Sodium Citrate + Salicylic Acid + Citric Acid + Water
Basically depending on pH, part of Sodium Citrate will swap Citrate with Salicylic Acid and form soluble in water Sodium Salicylate + Citric Acid.
pH stability for salicylic acid is from 3-4
It is not a stability pH. Salicylic acid in skincare is stable under any pH. It is the lowest pH you can reach in skincare products without being regulated and without precipitation in water-containing solutions.
is salicylic acid will be affected when added to a solution with a pH of 7 or 9 or buffer solution of sodium citrate?
Not sure what do you mean by this. Any acid is affected by rising the pH. The higher pH - the less acid in free form. In your example some of the acid becomes Sodium Salicylate. And that’s fine.
Please I need your answer.
I would suggest searching the forum because questions about Salicylic Acid were asked many times (including from myself haha)
-
Thank you for your answer.
But what do you mean by this : Basically depending on pH, part of Sodium Citrate will swap Citrate with Salicylic Acid and form soluble in water Sodium Salicylate + Citric Acid.
What do you mean by depending on ph, is it the ph of the final formulation or only after adding sodium citrate.
And what will I get in the final formulation
Salicylic acid serum or Sodium Salicylate?
-
Is it the ph of the final formulation or only after adding sodium citrate.
The final pH of the solution. The lower pH - the more acid inside.
And what will I get in the final formulation
As I said you get a mix of original Sodium Citrate, Sodium Salicylate, Citric acid and Salicylic Acid.
The lower pH - the more SA in the solution. But the lower pH - harder to keep it dissolved. If you use only water and Sodium Citrate I don’t think you can get 2% of SA soluble in water under pH 3.0 (but if you raise it to 4.0 most of SA becomes Sodium Salicylate and it is soluble in water)
-
Thank you.
-
-
-
-
Thank you for your answer.
But what do you mean by this : Basically depending on pH, part of Sodium Citrate will swap Citrate with Salicylic Acid and form soluble in water Sodium Salicylate + Citric Acid.
What do you mean by depending on ph, is it the ph of the final formulation or only after adding sodium citrate.
-
Certainly! The pH of a solution can significantly affect the stability and activity of its components, including active ingredients like salicylic acid. Salicylic acid is most stable and effective at an acidic pH, typically around 3-4 https://labmuffin.com/fact-check-friday-why-does-ph-matter-for-ahas-and-bhas/ block blast. This is because salicylic acid has a pKa of approximately 2.97, meaning it prefers to stay in its non-ionized form at this pH, which is crucial for its ability to penetrate the skin and exert its effects.
Log in to reply.