When is pH not relevant

Hi All
Just looking for some general guidelines for when pH Is not relevant
Ie how much water is needed in a formula to get a accurate pH?

I am making a face cleanser with a high concentration of oils and surfactants it leaves 45% water.
Is there a need to measure and adjust pH?

Same for w/o emulsions is pH relevant?

Comments

  • PH is relevant  in all cases where water is present even at 1-5% wt/wt 
  • Bill_TogeBill_Toge Member, Professional Chemist
    because pH meters are electrochemical devices, the relevance and reproducibility of any readings depends on the conductivity of the product, which in turn depends on its composition

    as the conductivity decreases (whether this is due to a lack of ionic salts, or the presence of non-conductive co-solvents), the measured pH readings will become less accurate, less consistent and less meaningful overall

    in anhydrous products and W/O emulsions, the continuous phase generally has little to no electrical conductivity, so any readings are essentially meaningless
    UK based cosmetic chemist with 13 years' experience at the bench. I've worked with pretty much everything apart from pressed powders, soap, solid lipstick and aerosols.
  • MicroformulationMicroformulation Member, Professional Chemist
    Good quality pH meters will adjust and account for the lower water content and conductivity (as well as temperature). Of course, if you don't have one to this standard, it is much less accurate.
    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.
  • Hi,

    Ok thanks Bill_Toge yes thats what I was taught so in general manufacturers I know dont even bother reading the pH of w/o or adjusting pH....
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