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W/O pH
Hi everyone. I’m still new to formulating and this forum has been of great help, so thanks a lot.
I have a problem though, I need to know how to check pH of W/O emulsions. Does it work like O/W normally does?
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3 Replies
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You can’t check pH of a W/O, since it is not defined. You can however, check the pH in the waterphase before making the W/O emulsion.
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David said:You can’t check pH of a W/O, since it is not defined. You can however, check the pH in the waterphase before making the W/O emulsion.Oh, ok. Thanks David. But then I don’t need to worry about the pH changing after I make the emulsion right?
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Some formulations do change pH after emulsification. For example such which contain pH active ingredients like free fatty acids, salts thereof, or certain ionic emulsifiers (sodium stearoyl lactylate or glyceryl stearate citrate).In this case, you could centrifuge the final emulsion until it separates and then measure pH in the water phase. Diluting with plain water to achieve easier phase separation can work but may result in false pH values for example in the case of fatty acids and salts thereof (stearate vanishing creams may change pH by several pH units upon dilution!). In that case, some advice adding alcohols (isopropanol or octanol) to break the emulsion; there still is the issue with possible pH fluctuations though less often and less pronounced than observed with water as diluent.Universal indicator paper may work. Unlike electrodes, these are less shielded by the oil as outer phase and may suck up the inner water phase to give a reading. Depends a bit on your product whether or not paper strips are working (given that you trust indicator paper).
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