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How to check PH for higher viscosity lotion
Hello everyone. Is there a way to test the ph for thicker solutions like lotion and creme if I don’t have an electrode made to handle thicker solutions? I read that I can dilute the lotion with distilled water at 1:10 ratio….but this just seems like the dilution would also lead to an inaccurate reading.
Any thoughts and or work arounds?
Any help would be much appreciated. Thanks in advance
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20 Replies
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dilute with 50% with water .
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If you increase the temperature, the viscosity should decrease.
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@em88, can’t you test the pH prior to the lotion reaching final viscosity, like before the cool down phase where it is still pretty fluid? I’ve never been quite sure when to test the pH.
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@em88 Very interesting I’ll have to try this. BTW would heating in any way diminish the efficacy of any actives specifically anti-microbials?
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@amitvedakar Thank you for the info. Can you elaborate a little more? Are we talking about distilled water? Also wouldn’t the PH of the water effect the ph of the lotion thereby changing the ph?
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@Yoyomel, it depends on the ingredients you are using. Check if any of your substances is thermolabile. For example if you use parabens as preservative, heat will not be a problem.
As tanelise said, you can check the pH before you cool it down. -
I’ve seen the dilution method too, but doubt also if that gives an accurate reading.
Tanelise’s tip is a good one I think. Keep in mind though that pH is temperature dependent and shows a more acidic reading at higher temperatures.
Yes, use distilled/deionized water (the same water you use for your buffers, if you prepare those yourself). -
@Doreen81, thanks. Good to know. Is there an “ideal” temp to test pH?
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Generally for such regular products like creams and lotions an ideal temperature would be 25 C for measuring a pH. But this is what I do, others can chip in with further insights here.
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@Chemist77, great thank you!
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pH changes with temperature. You can google that to see the details. In fact, some of the better pH meters have a temperature probe in the pH probe and the equipment accounts for the differences in conduction.
We have used a 50% dilution for pH in the past. Keep in mind, that we did NOT use it to project a final pH of the finished product for all the associakted reasons, but rather as an unrelated measure so that we could replicate this 50% value in production to ensure a consistent final product.
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Of course pH is temperature dependent, and professional pH meters measure the temperature in the same time. And yes, the room temperature is the usual temperature to measure the pH. By increasing the temperature I was referring for several grades not till the point the product is melted.
What kind of electrode do you have? It may work for semi-solids too.
Here are some info regarding electrodes
https://www.fondriest.com/pdf/thermo_ph_electrode_hb.pdf -
@em88, thanks for the pdf on the electrodes. I think I’ve read every thread on which pH meter to buy. Daunting to say the least.
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You can test pH of your
product at different dilution (with deionized water) … you will certainly observe a flat curve up to 1/10
dilution. Higher dilution should affect the pH -
@tanelise
You’re welcome. Sometimes it is necessary or inevitable to take measurements and make adjustments when the temperature is still higher than room temperature (like in some cases where too low a pH during the time of cool down can cause precipitation, I speak from experience). I just keep in mind then that the pH will be slightly lower when it’s warmer. Final pH adjustment I always do at room temperature, as this will be the temperature the final product will be stored at.
My (new) pH meter also measures temperature. It also comes with a probe which is designed for emulsions/higher viscosity and it’s very easy to clean. Probes that aren’t designed for emulsions can clog at the junctions.@Yoyomel
Distilled water can be sligthly more acidic as it absorbs carbon dioxide from the air. It’s not a problem to use it.
As em88 pointed out, it depends on the type of preservative if it can withstand elevated temperatures or not. Parabens indeed aren’t very heat sensitive, but some organic acids, e.g. potassium sorbate, should be added below 40C (≥60C causes it to sublime). -
@tanelise, @Doreen , @em88
Thank you all for the abundant replies. Perhaps I should have been more clear with my initial scenario.I’m currently adding my actives (anti-microbials) to an already premade lotion base. The lotion base has already been ph balanced but I would like to check PH after I add the powdered actives. Therefore the cool down phase would not apply in this situation.
I’m still undecided on how best to do this especially after reading all the wonderful replies. Heating a sample of the final product and testing ph seems like a good option but @Doreen reminded me that ph is temp dependent. I’m trying to reach a range in between 5-6 ph. How much more acidic of a reading would warming the product produce?
And the dilution method with DI water still escapes my mind. If DI water is say 7ph and my lotion is 3ph, wouldn’t adding these two ph numbers equate to something in between hence giving me an inaccurate reading?
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If the base lotion has a very high viscosity, how do you know that after adding the powdered ingredients you are getting an homogenous product? It is very difficult to incorporate powdered ingredients in a high viscosity mass. In these cases it is recommended to dissolve the powdered ingredients or to heat the mass at some point it is easier to incorporate powdered ingredients.
Try to make a water base dilution with the exact concentration of those ingredients you are adding and check if those ingredients do cause pH change. -
why do you need a pH of 5-6? is it for marketing reasons?
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@em88
This is very helpful. I was thinking the same thing therefore I will probably dissolve the powdered ingredients in a small amount of water before adding to the cream base. The other option you mentioned for heating the cream base worries me a bit for fear of reducing the efficacy of any ingredients but my worries might be unwarranted. Below are the ingredients for the cream base, only.Lastly, I’m slightly unclear regarding your last comment: “Try to make a water base dilution with the exact concentration of those ingredients you are adding and check if those ingredients do cause pH change.”…Can you elaborate more?
Once again I would ultimately like to check ph of the final product after the powdered ingredients are added.
Thank you again for your time!
Inactive ingredients (cream base): Water, Organic Coconut Oil, Grapeseed Oil, Emulsifying Wax, Stearic Acid, Glycerin, Xanthan Gum, Phenoxyethanol, Tetrasodium Glutamate Diacetate
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My idea was to check if those powdered ingredients that you add, at the concentration you are using, will or will not induce a pH change in a water solution. For example if you will not notice any pH change in the water solution, there might be a good change that the pH of the cream you are making will remain the same as it was in the beginning (base).
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