EDTA at pH 5 for calcium & magnesium chelation

Does EDTA chelate calcium and magnesium at pH 4.5 or 5 effectively?


  • PharmaPharma Member, Pharmacist
    Depends what you define as 'effectively'.
    For cosmetic purposes, magnesium is never chelated good enough to be of any benefit and calcium, especially at low pH, is nearly as poorly bound.
    In general, I wouldn't use EDTA for chelation of magnesium and only for certain applications when it comes to calcium (e.g. cleaning chalk deposits or in in vitro tests).
  • @Pharma by effectively i mean effective when shampooing the hair in very hard water. 

    What is the lowest pH at which EDTA can chelate calcium effectively in very hard water for Shampooing?

    How about citric acid @ ph 5 for calcium chelating? 
  • PharmaPharma Member, Pharmacist
    Ah, in a shampoo... well, it could work... theoretically.
    You'll have to try. For hard water you'll roughly need 600 mg EDTA for every liter of water you want to turn soft (if one neglects all the detergents, salt and what not within your shampoo). This means you can soften the part water used to produce lather with less than 100 mg EDTA in one application of shampoo but you can't soften all the water used to rinse off your shampoo at the end and that might spoil all attempts at softening tap water without a 'technical' water softener.
  • @Pharma thanks for such explanation.

    How much citric acid would i need for 1 litre hard water at pH 5?
  • PharmaPharma Member, Pharmacist
    Citric acid at pH 5 doesn't complex calcium ;) .
  • @Pharma ohh
    Should the pH be higher or lower for citric acid to complex calcium? 
  • PhilGeisPhilGeis Member, Professional formulator
    EDTA does disrupt microbial biofilm.  
  • PharmaPharma Member, Pharmacist
    Abdullah said:
    @Pharma ohh
    Should the pH be higher or lower for citric acid to complex calcium? 
    Although: Does your tap water really have a pH of 4,5-5? Do you live in a peat bog?
  • @Pharma no, pH of the Shampoo is 5. 

    I thought the pH of Shampoo and chelating agent in Shampoo will have effect in hardness of water with which we wash our hair. Is my thoughts wrong?

  • @PhilGeis thanks
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