I remembered that some workers (sorry I forgot their names) use potentiometric titration method with k3{Fe(CN)6} as titrant to determine the concentration of dye and sulphite in a single run. Some workers use Na2S2O5/NaOH as titrant.
I would like to introduce a company "Metrohm" to you. This company is manufacture auto-titrator and have huge research in titration that apply to industrial and may be you can find out some hints. I think the "Gold ring electrode" form Metrohm, or a redox electrode from other manufacturer such as Orion, is suitable in this titration work. For details, please search
www.metrohm.comThat is all information that I can provide to you.
Good luck!