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Precipitation and gel incompatibility salicylic acid serum
Dear all,
I am trying to formulate a salicylic acid serum.
I have two problems :
1. Phase B upon mixing yields a clear solution, but once mixed with A1, a white flaky preciptation happens and the sodium hyalouronate gel become thicker, like plastic gummy appearnce ( similiar to chewed gum, please excuse my metaphor)
I use a stock of 2% sod HA to provide a 0.25% sod HA in the formula
2. I cannot dissolve allantoin at all ! maybe there is something I am doing wrong, but I did a little experiment and it took approximately 100 mL of water (70 C) to dissolve 200 mg of Allantoin in presence of 2% urea.
What might be causing this problem ?
And should I use another gelling agent for thickenning the serum ?
I hope you are not dissapointed with my limited knowldge, I have a phD and masters in oral drug delivery, but still a beginner in cosmetics formulation.
the formula is as follows
A1 Water 65.650
A1 Xanthan gum 0.250
A1 High molecular weight sodium Hyalouronic acid 0.250
A1 Disodium EDTA 0.100
A2 Sodium citrate 1.000
A2 Urea 2.000
A2 Allantoin 0.250
A2 Glycerine 2.000
A2 Sod Citrate 1.000
A2 PEG 400 2.000
B Propylene Glycol 19.000
B Salicylic acid 2.000
B Mandelic acid 1.000
B Polysorbate 80 1.000
C Chamommile extract 1.000
C Grean tea leaf extract 0.200
C Phenoxyethanol 0.800
C Na benzoate 0.500
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3 Replies
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Couple of issues:
(1) Higher molecular weight HA and Xanthan Gum are generally incompatible. If you want to use Xanthan Gum, you’ll need to incorporate an HA less than 50kDA that won’t gel.
(2) Allantoin: Incorporate it in water heated to 50-55 C. It will go right into solution. If you use more than 0.5% Allantoin and/or incorporate at temperatures greater than 55C, the Allantoin will precipitate out of solution.
(3). Increase your solvent for the HA to 35%. You can cut back on the amount of Sodium Citrate to a 1:10 ratio of SC:SA. Heat the solvent to 70C or so and then add the SA.
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Thank you so much Mark, I will do as you suggested
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Hello Mark! Could you please tell me what’s the reason of the incompatibility between HMWHA (~1000-1500 kDa) and Xanthan Gum and how should it look like? I’m curious, because I have used both of them in different tests and they seem to be fine together, but maybe it needs some more time to show and more testing. I’ve also used this combination (HMWH/xanthan gum) in a low pH formulation, and that was the only time I saw that something wasn’t right, beacuse most part of the serum became thick, jelly-like after a few months, and there was also a little part of liquidy something at the bottom of the container. The pH stayed constant though through the whole testing. I’m suspecting the HA and starting the knock-out tests now. Any explanation or idea would be appreciated. 🙂 Thanks!
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