How to check PH for higher viscosity lotion — Cosmetic Science Talk

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
Tagged:
Tagged:

Comments

  • dilute with 50%  with water .
  • If you increase the temperature, the viscosity should decrease. 
  • @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.
  • @em88 Very interesting I'll have to try this. BTW would heating in any way diminish the efficacy of any actives specifically anti-microbials?
  • @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?
  • @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?
  • 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.
  • @Chemist77, great thank you!
  • 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.
    markfuller@microformulation.com Microformulation.com Microformulation Cosmetic Consulting provides Custom Formulations for both large Commercial accounts as well as smaller entrepreneurs. We can provide Naturally compliant Formulations under the NSF, NPA, Whole Foods and USDA Organic Certifications.
  • 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. 
  • 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).
Sign In or Register to comment.