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Preserving unstable actives
I’ll take Vitamin C as a typical example of an unstable active. Quite stable when dry, the minute you make an aqueous solution of it, the activity disappears. Oxidation appears to be the culprit. And so, in my latest design, I’m using a free oxygen radical scavenger to help preserve the activity.
But here’s a question:
In an aqueous solution, where is this free oxygen coming from? The oxygen atoms are bound to the hydrogen atoms by powerful bonds. Getting oxygen from a water molecule involves releasing hydrogen. So it’s not that. Presumably it is the dissolved oxygen.
Therefore I ask this: in order to remove free oxygen radicals from our formulae, should we not only use RO water, but also boil it immediately before use, to drive off the dissolved oxygen? -
18 Replies
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it’s mostly oxygen from the air; if a solution containing a reducing agent is exposed to the air, it will draw the oxygen from the air, and if the solution has a low viscosity, any oxygen introduced into the product will rapidly diffuse through it
perm lotions are a good example of this; the thioglycolic acid in the perm will readily pull the oxygen from the air, creating a pressure differential between the inside and the outside of the container, and if the head space is relatively large (e.g. if the container is partially filled) this causes the sides of the container to warp
permanent dyes, which are usually high viscosity and non-Newtonian liquids, are also a good example, as oxidation in this case causes visible discoloration of the product; because the product is non-fluid, the rate of oxygen diffusion through the product is very slow/zero, and oxidation only occurs near any surfaces exposed to air
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Perform all processes under a blanket of inert gas when working with oxidation sensitive materials.
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@Bill_Toge absolutely brilliant explain, was having an issue with my hypochlorite product. Now i have 2 variables, head space and viscosity to consider. Thank you again for such a brilliant insight.
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We used to purge the solvent (water) with Nitrogen gas in a vacuum chamber to drive off the dissolved oxygen. It’s a lot easier to use one of the more stable forms of Vitamin C such as magnesium ascorbyl phosphate.
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Oh, I already AM using a more stable version than MAP even. It is just that even so, the safe shelf life is only around 4-6 weeks. (Dark airless pump of course). Apparently pine bark extract will greatly extend shelf life. I was going to use eve-resveratrol but the solvency problem is too much to deal with.
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Have you tried an Ethoxydiglycol “blanket”?
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“Have you tried an Ethoxydiglycol “blanket”?”
Can you explain, please?
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Yes, the Ethoxydiglycol reduces the water activity. This is a very common approach to stabilizing Ascorbic Acid serums.
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The thing that raised my curiosity was the use of the term “blanket” in this context. I was considering that “blanket” was a covering.
Thanks for your explanation.
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@MarkBroussard what kind of percentage would typically be used for this purpose?
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About 40% Ethoxydiglycol … most often it is combined with about 15% propylene or ethylene glycol to bring to total glycol % to 55% or so, with 45% of the solvent base being water.
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Hi Belassi,
Have you tried using vitamin C glycoside? This is claimed to be a slow release, stable form of vitamin C that I understand is quite popular.
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I’ve got the pine bark extract now. These reports convinced me to use it:
http://naturalsociety.com/can-this-little-known-pine-bark-solve-skin-aging/
http://www.cosmeticsdesign-europe.com/Formulation-Science/Study-suggests-pine-bark-extract-contributes-to-skin-hydration-and-reduces-pigmentation
I made a 500g test batch a few days ago and the pine bark extract turned a nice pink/beige colour when the pH was 6. Airless container
L-Ascorbyl 2-Phosphate 6-Palmitate Sodium (Apprecier) is the main active, with pure glycyrrhizic acid and the pine bark extract as the other two. They all have different anti-melanocyte action. It’s just a guess, but I am hoping the combination may be synergistic. -
Hi Belassi,
Out of curiosity and because I am new to this site, please could you explain to me why you would discount using ascorbyl glucoside. Is it based on cost and if so, how much cheaper would it need to be to gain your interest.
This would be very interesting for me to understand as a chemist interested in cosmetic ingredients.
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Our test results were so impressive that I don’t want to risk not achieving the same by changing the main active ingredient.
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By test results, you mean in terms of formulating well, because my understanding (which many be misinformed) is that the concentration of vitamin C will be very low.
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No, I mean what happened with the testers who tested our first batch. Their skin before/after. I already formulated an anti-aging cream that has all sorts of actives (pea protein peptides etc) that was our most effective product and outsells all our other skin creams, but the vitamin C product easily outperforms it. Concentration 1%
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Excellent. Thanks for the clarification Belassi!
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