pH drop in emulsion

edited July 2014 in Formulating
What would cause a pH drop by about one point in an emulsion? It is stabilized by carbomer/TEA. Is this a sign that it is destabilizing? All other parameters are in spec.

Comments

  • MakingSkincareMakingSkincare Member, Professional formulator
    Can you give the full formula in %? It's hard to troubleshoot without this.
    Jane Barber
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  • Chemist77Chemist77 Member, PCF student
    Check the microbial profile, it brings the pH down if there is any contamination. Or maybe the acid component/carbomer of your formula was not completely neutralized and now on standing the alkali has reacted with acidic components bringing the pH down.
    I cant think of 3rd reason without knowing formula profile.
  • Hi All!  Sorry I wasn't able to get back to you until now.  Here is the breakdown of the fomrula:

    Acrylates/C10-30 Alkyl Acrylate Crosspolymer 0.1 (not actually a carbomer)

    Arnica Extract                                                  0.1

    Cetearyl Alcohol & Polysorbate 60                6.0

    Polysorbate 80                                                  4.0

    Methyl Salicylate                                               10.0

    Vanillyl Butyl Ether                                             0.4

    Glyceryl Stearate                                               3.0

    Isopentyl Diol                                                      2.0

    o-Cymen-5-ol (preservative)                             0.1

    Ethylhexylglycerin (preservative)                      0.75

    AMP (sorry - not actually TEA!)                        0.09

     

    The formula started out at a pH of about 7, and over 2 months has dropped to about 5.7.  I don't understand.

     

  • BobzchemistBobzchemist Member, PCF student
    It happens - that's why we do stability tests. Have you considered using a pH buffer?
    Robert Zonis, Sr. Formulation Chemist, Beaumont Products "All opinions and comments expressed are my own, have no relation to Beaumont Products, are fully copyrighted, and may not be used without written permission."
  • That is my next step, Bob. I was just wondering if anyone has seen this type of thing happen in an emulsion, and is a pH drop like that a destabilization route? 
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