PET testing

When is the best time to preform PET testing for a new formulation?  90-days when stability is done and approved or at another juncture?


  • PerryPerry Administrator, Professional Chemist
    We did it at two points.

    1.  Initially when stability testing began.
    2.  Next at 8 weeks of stability with samples at 45C
  • @Perry
    May I ask what is the purpose for doing it initially?  I assume since I am doing just regular micro and have done a 50 degree stability (initially) that might have covered any thing on the front end.

    If a sample exhibits some growth or is not up to expected standard then reformulation with a new preservative system will be in order?
  • PerryPerry Administrator, Professional Chemist
    I guess the idea is that you want to make sure that your batch initially  was not contaminated.  Yes, if a sample exhibits growth then you would reformulate. That way we didn't have to wait 8 weeks to see if the preservative system was going to fail. 
  • awesome thank you!!!

  • PhilGeisPhilGeis Member, Professional formulator
    edited November 2021
    You need to test the product as the consumer sees it - as well as the projecting its safety in rapid aging. Confirm with  real time aged product the data you see with rapid aged product.

    PET (presume USP) is a pretty poor test - so  all tested products must pass as bare minimum to justify consumer exposure.  Suggest you show it passes as made and after 1  month both ambient and rapid aged before you put it on the shelf for consumers.   And all ageing studies must be with product in final packaged. 
  • Just another question about PET....
     I do initial micro testing at the beginning and end of stability. When I make the initial bulk sample for stability, I was going to make enough regular stability and for the PET (150 grams) to sit at room temp till it is time for testing (3 months).  I wanted to avoid having to make it at the end of 3 months.  My thoughts were if this sample is sitting for 3 months at room temp this would be a good time to do PET in addition to the regular micro. Is this a decent idea?
  • MarkBroussardMarkBroussard Member, Professional Chemist

    You might want to do a micro test on your RT PET sample every couple of weeks to see if you are detecting any growth so you can pick up early on in the process if you have a preservation problem.
    Chemist/Microbiologist formulating in the Organic & Naturals arena under ECOCert/Natural Products Assn/Whole Foods/National Organic Program guidelines focused skincare & haircare products. 

    See website for details
  • PhilGeisPhilGeis Member, Professional formulator
    edited November 2021
    Process issues are best detected by sampling surfaces and intermediates during process - not finished product afterward.
  • @PhilGeis thanks again!
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