Impedance: I measured solution resistance of an anionic dye + arsenite system using Pt and ITO electrodes. I found different resistance. What might be the reason?
What you interpret as solution resistance is R1 (the low resistance in the high frequency range). ITO has a significant resistance value (especially for a lateral contact). R1 is influenced by the electrode resistance, but the solution resistance itself isn't. If you need an accurate measurement for solution resistance don't use EIS, but a conductometric device.
Experiment suggested to understand the case: re-do the experiment introducing a 500 ohm resistor between the WORK electrode and potentiostat and compare the results.