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I am studying the electrolytic determination of copper content in brass (~58% copper, ~40% Zn and other trace elements) by using standard method BS EN 16117-1:2011.

Now the electrode used for the electrolysis are both platinum material electrode. Normally the copper ion in electrolyte moves to platinum cathode to form copper. After the electrolysis done, the electrolyte is colorless, the cathode is brown because of copper. Normally the platinum anode is unchange in its "silver" color however it is not in my experiment, the anode is brown too! I don't understand what happen in anode.

I try to put the "colorized" anode in a nitric acid solution (50%) to try to dissolve the "color" but it didn't work. Can anyone tell me why this happen and how to solve the problem in reserving the platinum anode? Please and thanks for reading my question.

(Some information in making electrolyte: 2.5g of brass was dissolved in (15mL 40g/L boric acid, 2mL HF, 30mL 50% nitric acid, neutralized with NH3 solution and reacidify with 50% nitric acid, make up to ~300mL with water and add one drop of HCl, as stated in the stardard method) (Electrolysis environment: constant current, about 1-1.5A)

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