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ph changing in stability test
Greetings,
I am working on a cream and I have noticed that the pH changes over time in the stability test, more noticeable in accelerated conditions.
Ingredients: Methyl salicylate, menthol, sodium cetostearyl
sulfate and Cetostearyl alcool, xanthan gum, glycerine, waterI have noticed in the preparation process, if I melt the oil phase at 60-70 C the pH is around 6.5 and it drops to 6 after a month is the stability in accelerated conditions
If I melt the oil phase at 50-60 C the pH is about 7.5 but it drops to 7 in normal conditions and 6.1 in accelerated conditions (1 month).What might be the cause?
Thank you
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5 Replies
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Breakdown of menthyl salicylate to acid??
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at a guess, the fact there are no salts that can act to stabilise the pH; something as simple as disodium EDTA can be very beneficial in this regard
however, my bigger concern is that there appears to be no preservative
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@Chemist77, good point. I thought methyl salicylate was stable.
@Bill_Toge, I was thinking of adding something to stabilise the pH. Thank you for the suggestion. Regarding the preservatives, I have seen several similar products in the market and none of them had preservatives. I guess having a high % of methyl salicylate and menthol was enough to avoid preservatives.
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@em88 it is purely a guess, since pH is involved and the only logical point is presence of a component responsible for pH drop.
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Has anyone else faced this?
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