# Measuring pH in ferric oxalate solutions

I have a problem with measuring $$\mathrm{pH}$$ in ferric oxalate solutions ($$\sim 5~\text{to}~\pu{10 g L-1}$$ $$\ce{Fe},$$ $$\pu{0.8 M}$$ oxalic acid, $$\pu{25 °C}$$). While I am sure about the $$\mathrm{pH}$$-meter device and buffer solutions ($$4$$ and $$7$$) and also the good function of my electrode (Sentek) in other solutions, the $$\mathrm{pH}$$ value does not stabilize at all in such a way that it continuously decreases as far as the pH becomes negative and eventually, under-ranged.

Is there any interference or any requirements for $$\mathrm{pH}$$ measurement in oxalate solution?

• What is your $\ce{Fe^3+}$ source? – Mathew Mahindaratne May 27 '19 at 22:29
• Can be interfering eventual draging out calcium ions from the electrode glass ? – Poutnik May 28 '19 at 5:25