pH drift w/ Geogard ultra in lotion formula

LongXiLongXi Member, PCF student

Hi everyone, my name is Rani, I'm a new formulator in Los Angeles who is learning cosmetic formulation with the goal of starting a natural/sustainable skin & hair care company. This is my first post.

I've been testing out some formulas (see photo) with Geogard ultra as my preservative, and after 2 weeks the pH of my various lotions using this formula have drifted from around 4.5/4.6 to 3.9/4.0. I didn't use sodium citrate in them. I've read various threads and tried to research the process online but I've not been able to find any material that explains the pH stabilizing process. The instructions given are:

1. Dose the final product with the required level of Geogard Ultra™ along with a 1.5x amount of sodium citrate. So, a 2% dose of Geogard Ultra™ should be accompanied by 3% sodium citrate
2. Mix thoroughly to ensure all solids have dissolved and adjust the pH of the formulation to 7.00-7.25 with 30% sodium hydroxide
3. Finally, adjust the pH to desired final product pH (pH 5.4–5.5 is ideal) with dilute sodium hydroxide or citric acid solution


And my questions are:
1. Do I add the sodium citrate in the water phase before I emulsify with my oil phase, and then continue to the sodium hydroxide step?
2. Do the sodium hydroxide and citric acid both need to be made into water solutions? The instructions say 30% sodium hydroxide, which is unclear.
3. Why do I need to raise the pH with the sodium hydroxide only to lower it again with citric acid?

Thank you for your assistance. Peace & Blessings.

Comments

  • @LongXi You really need to add the Sodium citrate. At the pH you mentioned, it'll be in equilibrium with its former acid (Citric acid), which will help buffer the system, controlling pH drifts. Sodium citrate has to be added before your preservatives. Citric acid and Sodium hydroxides are added to reach your final pH, you don't need to use both, only the one that can make your reach your final pH, and it's better to dilute them first, for proper incorporation.
  • LongXiLongXi Member, PCF student
    ketchito said:
    @LongXi You really need to add the Sodium citrate. At the pH you mentioned, it'll be in equilibrium with its former acid (Citric acid), which will help buffer the system, controlling pH drifts. Sodium citrate has to be added before your preservatives. Citric acid and Sodium hydroxides are added to reach your final pH, you don't need to use both, only the one that can make your reach your final pH, and it's better to dilute them first, for proper incorporation.

    Thanks for your response Ketchito. That does clarify things a bit.

    So I would add the sodium citrate into the water phase before adding the preservatives, then add the oil phase, homogenize, and then slowly add the citric acid or sodium hydroxide solution while testing with a pH pen. Did I get that right?

    This process seems impractical for creating sydnet bars if the pH adjustment is done on the final product. I may need to find an alternative preservative for my bars.

    Peace & Blessings
  • I use geogard ultra in my syndet bars.  I don't follow the buffering process, and have not experienced any ph drift with them.  I think it may have to do with the fact there is low water activity.
  • @LongXi

    Hello Rani.

    What I do with my stuff is I dump most of everything in one pot and mix. As long as I have good mixing too OR solution not too thick OR enough water, then it is fine (Citric Acid will be dissolved). I normally do not separate things phase this phase that, heat this that for this that long. Nope, no stability issue maybe I am using inorganic and unnatural stuff. LMAO!

    Yes, I do find that the buffer section of Lonza rather confusing. What I gather is they are saying make Sodium Citrate on site. But redundant steps and extra substances used.

    I make Sodium Citrate on site because I have no Sodium Citrate and I do not want to buy it when I can easily make it. I mix Sodium Bicarbonate and Citric Acid in one pot. No good and valid reason that I should have extra steps to achieve the same result. Crazy to first put in Sodium Citrate then put in Sodium Hydroxide then finally put in Citric Acid.

    Gluconolactone (Glucono-delta-Lactone or GdL) will become Gluconic Acid (probably about 52%) after a while. I do not know how often you check pH. If pH changes only after two weeks then the temperature must be way way low.

    The trick to heat GdL. Yes, heat it. This will convert GdL to its acid form quickly and perhaps its 'final' form (for lack of better technical description on my part). Heat it with some water and test its pH...et voila! By the power of science vested in me, I shall say you are now pH stable! LOL!

    Do not believe in people saying preservatives should be put last or that they are heat-sensitive. Not every preservative behaves the same.

    GdL is not even a preservative! The converted Gluconic Acid is also not a preservative! I mean, they are lousy preservatives but only if pH is very low.

    Organic acids are weak preservatives and definitely rendered nearly useless if you want to raise pH to that so-called "skin friendly" level as some of them turn into their salt form. Salts are preservatives but only if they are in high concentration.
    If organic acids were excellent preservatives then big corporations would have used them because they are organic and natural, can save lots of money and minus extra step adding inorganic and unnatural preservatives.

    My love is DMDM Hydantoin because it will not only preserve under water but also above water (airspace). Other people see things growing on top of their products, but not me! Oh, DMDM Hydantoin has no known substance which de/inactivate it. Can be heated. Above all, I do not appeal to nature/organic!
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