[TJ2311]

Hello!

I am performing an EDTA titration with calcein indicator to measure the concentration of calcium ions and magnesium ions in milk. I have a issue with my calcein indicator because during the steps of standardisation the indicator does not turn pink (initial colour), but stays golden yellow (colour of my indicator). I initially thought I prepared my indicator incorrecly but my second batch also failed at turning pink. I am totally lost now, could someone please explain what I am doing wrong?

My solutions:

EDTA solution 0.025 M
CaCl² solution 1 M
NaOH 8 M (I am using this instead of KOH, because we don't have KOH solid to make 8M, but KOH of 2M, and 4M did not work either.)
Milk samples with different fat percentages

I followed this method: https://www.journalofdairyscience.org/article/S0022-0302(64)88575-1/pdf

Thank you

[Borek]

I am afraid you have not posted enough information. Besides, such thing are best troubleshoot by simplifying the situation step by step and patiently checking everything. Start with just plain water. Is the color of the indicator without calcium as expected? Does it change after modifying pH with the base? Does it change after adding calcium? Are these changes/lack of changes as expected? If yes: error is somewhere else. If not: this is a hint as to what is going wrong.