Quest for the Missing Salicylic Acid

Hello,

I am not a formulator, but I work in process validation for a contract manufacturer, and sometimes I get drawn into issues for newly formulated products.  In this case, we have pilot batches for two newly-developed products (skin cleansers).  Both are about 63% water and 7% glycerin, and both use Sodium Hydroxide as a PH adjuster.  One contains 2% (17kg) Salicylic acid, and the initial batch assay puts it about 1kg short (batch size is 850kg).  The second product is worse.  It contains 0.5% (4kg) salicylic acid, and the assay is 1.4 kg short (batch size is 800kg).  We have taken all the normal investigational steps (raw materials reconciliation, checked the filters, etc.), and we cannot find this missing material.

Does anyone have any experience with a loss such as this? So far, this remains a mystery. 

Thanks in advance for any help.

Mike

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Comments

  • johnbjohnb Member, Professional Chemist
    How are you measuring this loss?

    Remember that adjusting pH with sodium hydroxide will remove free salicylic acid.

    What is the function of this product? Usually a formulation containing salicylic acid requires the free acid, not its sodium salt.
  • Unknown Member
    edited September 2016

    This is our method

    "The analysis of Salicylic Acid is achieved by using reversed phase HPLC with UV detection at 305 nm with a C18 column. The quantitation of Salicylic Acid in the sample is achieved by the comparison of the peak area of Salicylic Acid in the sample chromatogram to that of a reference standard of a known concentration using external standardization."
    Prior to these issues, a lab batch was manufactured in which the Salicylic acid assay was within specification. 

    Facial cleansers.



  • Unknown Member
    edited September 2016
    Deleted repeated comment
  • BobzchemistBobzchemist Member, PCF student
    Are you checking for Sodium Salicylate?
    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."
  • BobzchemistBobzchemist Member, PCF student
    I've had this argument with analysts before - I put the correct amount of the ingredient in the batch, I made the batch and no residue was left over, but the assay shows less of the ingredient than I put in. 

    My feeling has always been - if the ingredient isn't volatile, and there's no evidence of it crystalizing or dropping out, then the analysis must be wrong - ingredients don't just vanish. 
    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."
  • I agree with Bob and John. I think some of your salicylic acid is converted to sodium salicylate by the addition of sodium hydroxide. 

    You can validate this by testing your production batch samples for salicylic acid and sodium salicylate. Compare the results and see if the results would add up.
    Formulator. Currently specializes in formulating natural cosmetics.
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