Home Cosmetic Science Talk Formulating General Buffer solution

  • Buffer solution

    Posted by free9s on April 22, 2024 at 8:40 pm

    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.

    • This discussion was modified 3 weeks, 6 days ago by  free9s.
    free9s replied 3 weeks, 5 days ago 2 Members · 5 Replies
  • 5 Replies
  • fareloz

    Member
    April 23, 2024 at 4:37 am

    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)

    • free9s

      Member
      April 23, 2024 at 5:35 am

      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?

      • This reply was modified 3 weeks, 5 days ago by  free9s.
      • fareloz

        Member
        April 23, 2024 at 8:37 am

        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)

        • free9s

          Member
          April 23, 2024 at 4:39 pm

          Thank you.

  • free9s

    Member
    April 23, 2024 at 5:33 am

    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.

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