How do you measure the pH of your formulations / products?

I'm very curious about this topic because I've heard many different types of measurements coming from formulators. I particularly prefer to use the pHmeter directly in the finished formulation. I don't really like the pH strips because they are not very accurate, but they do their job when needed. On the other hand, I've seen reports of people doing solutions to check this... but what would be the scale/proportion of that?

Are there other methods you know of? Which ones do you use? Help a curious one!

Comments

  • PerryPerry Administrator, Professional Chemist
    We used pH as a measure for formula quality. To that end using a pH meter where you can stick the probe into the product was fine.  Water based products like shampoo, conditioner, styling gel, lotion, and more worked fine this way.  It doesn't necessarily give a perfectly accurate reading of the pH, but it is much better than a pH strip and was consistent enough to be useful for QC.

    I know some people advocate taking a sample of a product, diluting it in water, then taking the pH but I've always found this unnecessary. 
  • Ahhh.....the much-maligned pH test strip. If you choose good quality strips, Merck for example, get the job done.

    Ok, but not to 2 decimal point accuracy.

    During my chemistry / biochemistry lecturing days it was a practical lab I would set for students. Identify pH standards in the food and cosmetics industry, tabulate these, then on a series of samples measure pH using a meter and test strips. They would then summarise the two sets of results and comment on the relative accuracy of both methods.

    In our own cosmetics manufacturing facility, I encourage our QC Manager to use pH test strips for IPQM. At the final stages, for example with batch retained samples, then the pH meter is used. Both sets of results are recorded and retained.

    It works for us. But again, we're talking good quality pH strips.
    Dr. Mike Thair
    Cofounder & Chief Formulator
    Indochine Natural
  • These are not too bad: Camlab 1138924 pH-Fix indicator stick, pH 4.5-10.0 with CE-Mark, 6 mm x 85 mm (Pack of 100) https://www.amazon.co.uk/dp/B06XRSYVYB/ref=cm_sw_r_cp_api_i_D34EHSBA8FRTWC93Z0T7

    but expensive. Plus you would need to purchase several ranges, because the narrower the range the more precise they are. On the bright side, you don’t have to calibrate them
  • I've found some really accurate pH strips. I've tested them against my Apera pH meter many times and they are always accurate. So I use pH strips because there's no other way to test emulsions other than making a 10% solution which I won't do because it's not accurate.

    I still use my pH meter for aqueous products though.
  • emma1985 said:
    I've found some really accurate pH strips. I've tested them against my Apera pH meter many times and they are always accurate. So I use pH strips because there's no other way to test emulsions other than making a 10% solution which I won't do because it's not accurate.

    I still use my pH meter for aqueous products though.
    Do you think that the measurement of emulsions in the pH meter is not accurate without the 10% dilution? In my experience I've always used it directly in the final formulation and it worked (I even compared it with the pH strips and found the same values)

    Is there a specific problem with this? I mean, I'm asking in general, if there's something that interferes with the measurement or if it's just the adhesion of the product to the equipment that is complicated to deal with
  • AbdullahAbdullah Member
    edited March 28
    emma1985 said:
    I've found some really accurate pH strips. I've tested them against my Apera pH meter many times and they are always accurate. So I use pH strips because there's no other way to test emulsions other than making a 10% solution which I won't do because it's not accurate.

    I still use my pH meter for aqueous products though.
    O/w emulsion is also like aqua's product because the continues phase is water. You can check the pH of o/w emulsion the same as pure water. 
    If you have w/o that would be hard to check the pH at the end so you should check it before mixing oil and water. 

    Making 10% solution is not necessary or accurate.
  • MicroformulationMicroformulation Member, Professional Chemist
    As @Abdullah mentioned, an O/W emulsion can be checked at full strength with a pH meter of the proper type.

    The last pH strips I owned were in my 6th Grade Chemistry Set.
    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. BS.Pharm Albany College of Pharmacy, Union University.
  • emma1985emma1985 Member
    edited March 28
    Rafacasti said:

    Is there a specific problem with this? I mean, I'm asking in general, if there's something that interferes with the measurement or if it's just the adhesion of the product to the equipment that is complicated to deal with.
    Just the inability to properly clean the pH meter. At least my pH meter. I would have dried up emulsion bits all around the diode.
  • ngarayeva001ngarayeva001 Member
    edited March 28
    pH meters are 1) expensive 2) pain in the neck to calibrate 3) pain not only in the neck to clean. Decimal point accuracy isn’t always needed. 
    I heard this probe is good in terms of cleaning https://www.tester.co.uk/extech-601100-flat-surface-electrode-15-x-106mm

    it’s just a probe not the whole ph meter

  • emma1985 said:
    Rafacasti said:

    Is there a specific problem with this? I mean, I'm asking in general, if there's something that interferes with the measurement or if it's just the adhesion of the product to the equipment that is complicated to deal with.
    Just the inability to properly clean the pH meter. At least my pH meter. I would have dried up emulsion bits all around the diode.
    In this case, my cleaning tips are:
     
    - When not using the pH meter, let the electrode "rest" in a KCl solution

    - If you intend to use it, wash the electrode with a gentle jet of water from a pissette (only water!)

    - Then dry the electrode with a paper towel (very carefully)

    - Measure the pH and repeat the cleaning process whenever you want to take a new measurement (ie: clean > dry > measure > clean > dry > measure...)

    - If you know you will be using the pH meter many times in a short period of time, you can let it "rest" in a beaker filled with water instead of KCl to avoid dehydration (but return it to KCl when you are done with all measurements)

    Note: Even if you are going to measure the same batch/same product, always clean the electrode before finishing the first measurement (and dry it with a paper towel). Even if you think "Hm, I'm just going to add 0.1% Citric Acid to adjust the pH of this formulation, I don't need to wash", clean it in the same way. It's easier to remove the emulsion when it's fresh. Remaining formulation on the electrode may change your results for the next measurements.


    [Here I'm used to do this process with a Gehaka 4200 (not sure if this brand is available abroad the country I live). If someone thinks this is not the correct way to do it, you can tell me. I just learned this way and never searched for something different because it works well]
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