Iso-electric point of allantoin

DoreenDoreen Member
in Formulating
Can someone tell me the iso-electric point of allantoin? Or where to find it or how to calculate it?
(I want to know for sure from which pH I can use it together with anionic substances.)

Thanks! :+1:
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Comments

  • PerryPerry Administrator, Professional Chemist
    edited December 2018
    According to Merck, the following is true of a 5% solution in water:

    pH = 4.5 - 6 (5% in water, 20 deg C)

    https://pubchem.ncbi.nlm.nih.gov/compound/allantoin#section=Vapor-Pressure
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  • DoreenDoreen Member
    edited December 2018
    @Perry
    So allantoin has a neutral charge between pH 4.5 and 6, below 4.5 cationic and above 6 anionic?
    Edit: Would it be very different if the concentration decreases to 0.5%, or lower?

    Thanks so much, Perry! :+1: :smiley:
  • SibechSibech Member, Professional Chemist
    @Doreen at 25 degrees C It is probably the same as the solubility is about 0.6% in water.
    Dabbling Formulator — Qualified Cosmetic Safety Assessor — experienced in claim substantiation & EU regulatory affairs.
  • DoreenDoreen Member
    @Sibech
    Ok, thanks a lot!!
  • PerryPerry Administrator, Professional Chemist
    @Doreen - well not exactly. I believe it is a weak acid so it wouldn't be correct to claim it's ever cationic. It either has a negative charged ion at lower pHs or it is neutral. See the structure of allantoic acid.


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  • DoreenDoreen Member
    edited December 2018
    @Perry
    You're right! I thought it had a negative charge at higher pH's.
    ( Ingredients To Die For is also mistaken I see: 'Allantoin is an amphoteric compound that is anionic under basic conditions.')
    Thanks for clearing that up! Now I know I never have to worry combining it with anionics.
    Thanks!!
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