How to use buffers in cosmetics

lewhitaklewhitak Member
in Formulating
Hello!
I've done a forum search but am still not getting this topic. When buffering a formula with something like lactic/lactate buffers, do you first adjust the pH of the buffer in water to your desired range and then add additional ingredients? Do you then again adjust the pH after adding additional ingredients like aloe?

Thank you!

Comments

  • ngarayeva001ngarayeva001 Member
    Buffer predicts the pH. For example, 1% of 88% lactic acid + 3% of 60% sodium lactate should lock the pH at 4.076 (my pH meter has only 2 decimal points though). Other ingredients might shift the pH and I wouldn't expect it to stay the same but at least in theory with a buffer that should shift less.

  • EVchemEVchem Member
    yep exactly as @ngarayeva001 said. You choose a buffer system based on the pH you want to be at
  • lewhitaklewhitak Member
    Ohhh, ok. I like that @ngarayeva001 - "buffer predicts the pH."

    How I get confused is in the case of buffering to stabilize an ingredient. For example, if a material is said to be stable using a pH 4.0 lactate buffer BUT after you add all the additional ingredients to the system you are more at a 4.5 or what have you. Do you then have to re-adjust to a pH 4.0? This is all theoretical, I haven't tried it because I was unsure of what I was doing.

    Thank you as well @EVchem!
  • PharmaPharma Member, Pharmacist
    lewhitak said:
    ...if a material is said to be stable using a pH 4.0 lactate buffer BUT after you add all the additional ingredients to the system you are more at a 4.5 or what have you. Do you then have to re-adjust to a pH 4.0? ...
    You don't add a lactate buffer but, in that case, just lactic acid and at the end, adjust to pH 4 with diluted sodium hydroxide or whichever base is proposed. Thereby, you create the pH 4 lactate buffer.
  • ngarayeva001ngarayeva001 Member
    Ok, since I have been struggling with it for years here is what I know:
    When the system is somewhere around neutral introducing 1% of lactic acid and 3% of sodium lactate will bring the pH to 4. Tested it many times for different pHs with Hanna pocket pH meter that is accurate to 1 decimal point (sorry I somehow thought it was 2 but I checked and it's 1).

    Here is what I don't know: when you use, say, glycolic acid at 5% the pH goes below 2. I want to bring it to it's pka value 3.8. I add all ingredients but lactic acid and sodium lactate, adjust the pH to 3.8, then calculate lactic acid buffer values for ph 3.8, which is equal to 2% of lactic acid and 3% of sodium lactate as per my calculator, and add those two. The pH doesn't change. Checked it after a month, still the same.  I am not sure if it's the correct way to do it and would really appreciate if @Pharma can shed some light here. Maybe I just was lucky.
  • DoreenDoreen Member
    Pharma said:
    lewhitak said:
    ...if a material is said to be stable using a pH 4.0 lactate buffer BUT after you add all the additional ingredients to the system you are more at a 4.5 or what have you. Do you then have to re-adjust to a pH 4.0? ...
    You don't add a lactate buffer but, in that case, just lactic acid and at the end, adjust to pH 4 with diluted sodium hydroxide or whichever base is proposed. Thereby, you create the pH 4 lactate buffer.
    @Pharma, what would you personally recommend for a pH between 4.8 - 6? (The 'pH (skin) neutral' range)
  • PharmaPharma Member, Pharmacist
    @ngarayeva001 A buffer has to be in roughly 10 x excess or more of compound X to accurately buffer said compound X. If compound X is a defined acid or base it may be turned directly into a buffer. It's a 'stupid' (no offence!) approach to add 5% glycolic acid and then try to buffer it with 5% lactic acid - sodium lactate. Glycolic acid buffers as good as lactic acid: Therefore, the way to go would be 5% glycolic acid and enough sodium hydroxide to bring the pH to the desired value. To obtain a pH of 3.8, 50 mol-% NaOH are required because that pH coincides with it's pKa. BTW a pH at the pKa is the sweet spot for any buffer.
    Calculating how much of buffer Y is required to adjust considerable amounts of substance X ain't a cakewalk! It's often easier to just go and add a strong acid or base to a weak base or acid, respectively, until the desired pH is reached.
    A buffer is usually effective over +/- 1 unit around the pKa of the used weak acid or pKb of the used weak base. This only holds true for conditions wherein a buffer is used at 10 x excess or more. At +1-2 or -1-2 units, the buffer will only work in one direction (towards the pKa).
    @Doreen CLICK and scroll down to page 14 (read the general stuff too, it's worth the time). As you can see, citrate, malate, and succinate would be useful. Unfortunately, not many standard Good's buffers are available for the slightly acidic range. MES is basically the only one (not my favourite for lab works or in/on humans) and is widely used in hydroponics (also not my favourite when it comes to plants). In cosmetics, you'll find for example HEPES (I like that more) in creams which use cell culture media (a marketing ploy); HEPES should be at +/- physiologic pH if done according to good buffering practice.
    My recommendation is: buffers are usually not useful in cosmetics. Simply adjusting pH is more often than not sufficient and creates a self-buffering product. If I had a gun to my head and were forced to use one for that slightly acidic range and couldn't use above mentioned carboxylic acids, I'd go with GLDA (Dissolvine-GL). It's usually used as chelate but buffers well at that pH range though it's a bit problematic with electrolyte sensitive formulations if used at buffer concentrations instead of chelate concentrations.
  • ngarayeva001ngarayeva001 Member
    It was my understanding that without a buffer pH might drift. I managed to work out Henderson-Hasselbalch equation for lactic acid buffer but my knowledge of chemistry isn’t on the level that would allow to account for all elements of a complex system. I saw ‘fruit acids’ marked at home crafters with lactic acid buffer. The pH of those ‘materials’ is locked at a level that is high enough that people without pH meter can’t hurt themselves, that is what brought the idea to buffer glycolic acid this way.
  • DoreenDoreen Member
    Pharma said:
    (...)
    @Doreen CLICK and scroll down to page 14 (read the general stuff too, it's worth the time). As you can see, citrate, malate, and succinate would be useful. Unfortunately, not many standard Good's buffers are available for the slightly acidic range. MES is basically the only one (not my favourite for lab works or in/on humans) and is widely used in hydroponics (also not my favourite when it comes to plants). In cosmetics, you'll find for example HEPES (I like that more) in creams which use cell culture media (a marketing ploy); HEPES should be at +/- physiologic pH if done according to good buffering practice.
    My recommendation is: buffers are usually not useful in cosmetics. Simply adjusting pH is more often than not sufficient and creates a self-buffering product. If I had a gun to my head and were forced to use one for that slightly acidic range and couldn't use above mentioned carboxylic acids, I'd go with GLDA (Dissolvine-GL). It's usually used as chelate but buffers well at that pH range though it's a bit problematic with electrolyte sensitive formulations if used at buffer concentrations instead of chelate concentrations.
    Thanks, Pharma! 
    I was thinking about citrate, as citric acid is easy obtainable, plus it's a polyprotic acid and covers a broad range.

    ''Simply adjusting pH is more often than not sufficient and creates a self-buffering product.'' 
    This is my personal observation too. I hardly notice any considerable pH shifts in my own stuff over time .
    And since it's for my own use and doesn't end up somewhere on a shelf in a store for a while, I don't need it to be stable for such a long time anyway.
  • PharmaPharma Member, Pharmacist
    Plus, a pH shift usually indicates something unwanted going on (degradation or microbial growth). Because degradation apart from rancidity and other smelly reactions isn't much of a concern in cosmetics (it should be but, well, it's cosmetics and a fair amount of claim ingredients does degrade before it's even packed), masking it seems like the logic thing to do...
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