Determination of Ca/Mg in orthophosphate-rich solutions

[Baho Ilok]

I want to measure the Ca and Mg concentration in a solution that contains up to 250 mg/L of PO₄^3-. 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!

 

[Borek]

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.

 

[Baho Ilok]

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.

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.