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Determination of Ca/Mg in orthophosphate-rich solutions

  1. Feb 6, 2017 #1
    I want to measure the Ca and Mg concentration in a solution that contains up to 250 mg/L of PO43-. Apparently, orthophosphates interfere with both flame photometric methods and complexometric methods with EDTA (or so I've read). Is there a standard method for measuring Ca and Mg in this type of solution?

    I am more preferring complexometric methods at the moment because our atomic absorption spectrophotometer is not functioning well. Thank you!
  2. jcsd
  3. Feb 6, 2017 #2


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    Staff: Mentor

    Complexometry is a gold standard here.

    Problem with orthophosphates is that for EDTA titration you need a high pH, and in high pH and in the presence of orthophosphates you can expect precipitation of weakly soluble magnesium and calcium salts. I am not aware of any standard method of dealing with such situations (doesn't mean there is no one, its been ages since the last time I had to deal with these titrations). I would check if there is no other chelating agent that works nicely in lower pH.
  4. Feb 6, 2017 #3
    I found one paper that proposed an alternative titration method that eliminates orthophosphate interference but it was published in 1961. I was wondering though that there was a standard method that I have not yet read about.

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