A method for monitoring the total amount of brighteners in an acidic copper/copper alloy plating bath during a copper/copper alloy plating process, the method comprising the steps: (a) providing a plating bath sample from said plating bath, the plating bath comprising (a-1) one or more than one brightener selected from the group consisting of and wherein n and m are independently 1, 2, 3, 4 or 5, and p is independently 0, 1 or 2, (a-2) copper ions (a-3) chloride ions, (b) adding to the plating bath sample (b-1) one or more than one redox active compound, which is not a compound of (a-2), wherein said redox active compound - exhibits a standard potential E 0 in the range of from - 0.80 V to + 1.45 V, and - is selected from the group consisting of metal ions, metal oxide ions, iodide ions, and molecular oxygen, such that a measuring sample results, (c) in a measuring unit comprising a working electrode, the working electrode being contacted with the measuring sample measuring a voltammetric or a chronoamperometric response of the working electrode by polarizing the electrode such that electrochemical current data are obtained, (d) optionally processing the electrochemical current data obtained in step (c) in order to obtain processed electrochemical current data, (e) comparing the electrochemical current data obtained in step (c) or the processed electrochemical current data obtained in step (d) with reference electrochemical current data or processed reference electrochemical current data. (a) providing a plating bath sample from said plating bath, the plating bath comprising (a-1) one or more than one brightener selected from the group consisting of and wherein n and m are independently 1, 2, 3, 4 or 5, and p is independently 0, 1 or 2, (a-2) copper ions (a-3) chloride ions, (a-1) one or more than one brightener selected from the group consisting of and wherein n and m are independently 1, 2, 3, 4 or 5, and p is independently 0, 1 or 2, n and m are independently 1, 2, 3, 4 or 5, and p is independently 0, 1 or 2, (a-2) copper ions (a-3) chloride ions, (b) adding to the plating bath sample (b-1) one or more than one redox active compound, which is not a compound of (a-2), wherein said redox active compound - exhibits a standard potential E 0 in the range of from - 0.80 V to + 1.45 V, and - is selected from the group consisting of metal ions, metal oxide ions, iodide ions, and molecular oxygen, such that a measuring sample results, - exhibits a standard potential E 0 in the range of from - 0.80 V to + 1.45 V, and - is selected from the group consisting of metal ions, metal oxide ions, iodide ions, and molecular oxygen, (c) in a measuring unit comprising a working electrode, the working electrode being contacted with the measuring sample measuring a voltammetric or a chronoamperometric response of the working electrode by polarizing the electrode such that electrochemical current data are obtained, (d) optionally processing the electrochemical current data obtained in step (c) in order to obtain processed electrochemical current data, (e) comparing the electrochemical current data obtained in step (c) or the processed electrochemical current data obtained in step (d) with reference electrochemical current data or processed reference electrochemical current data.