pH drift w/ Geogard ultra in lotion formulaHi 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 citrate2. Mix thoroughly to ensure all solids have dissolved and adjust the pH of the formulation to 7.00-7.25 with 30% sodium hydroxide3. Finally, adjust the pH to desired final product pH (pH 5.4–5.5 is ideal) with dilute sodium hydroxide or citric acid solutionAnd 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.