I synthesized a solution containing Cu2+ (0.5 g/l), Fe3+ (0.26 g/l) and Fe2+ (0.19 g/l) with hydrated sulphate salts and I followed iodometric method containing Starch solution (1 %wt), Na2S2O3 solution (0.1M), KSCN (1 g), KI (1 g) and NH3 and CH3COOH (at the first step of titration). Otherwise, I can’t reach the correct answer and I always calculate Cu concentration more than the 0.5 g/l. However, without Fe ions, I have reached to the answer only with 2% error. Additionally, the color of solution is completely different for these two conditions (Cu2+ with and without Fe ions). How can i measure Cu concentration at the presence of Fe ions?