Methods to detect iron in highly concentrated ferric sulphate solutions

I’m writing with a query related to reagents used to detect iron in highly concentrated ferric sulphate solutions.


I am currently exploring iron detection in both solutions of ferrous $\ce{(Fe^2+)}$ and ferric $\ce{(Fe^3+)}$ sulphate. I have had success with the detection of $\ce{Fe^2+}$ by performing potassium permanganate titrations which lead to accurate results. However, I am struggling to identify an appropriate reducing agent so that the method can be applied to solutions of ferric $\ce{(Fe^3+)}$ sulphate.


A potential option that I was considering was hydroxylamine hydrochloride. However, I am concerned about the potential quantities of $\ce{N2O}$ which may be produced at such high iron concentrations in the ferric sulphate I am using $(\approx \pu{18 gl^-1})$. Is anyone aware of this area of experimentation or aware of any such standard method for the detection of $\ce{Fe^3+}$ in this way?


