Can all of those indicators for EDTA titration testing substitute each other?

Question

I am doing an experiment testing Calcium content in milk but I do not have the Patton-Reeder indicator. Can all of those indicators for EDTA titration testing substitute each other? For say, Can I use Eriochrome T indicator instead and without changing any experimental steps?

Answer 1

Hi Sumiki H.,

I'm not an expert on milk titrations, but the literature does suggest that the only interference you are likely to encounter is from Mg (unless your cows were fed seaweed from Minamata Bay?). The endpoint (assuming you have normal color vision, which I do not!) would then become indistinct due to the differing specificities of EDTA vs. the indicator binding to the respective metals. I THINK the workaround would be to add KOH to precipitate any Mg as Mg(OH)₂ before the titration. Practically speaking, you should titrate identical milk samples both with and without that pretreatment, and see if you have a significant difference in assay.

Really, you can get this type of info yourself, Google the indicators and read up.

-- Cheers, --Mr. d.