Method for monitoring the total amount of sulphur containing compounds in a metal plating bath

A method for monitoring and adjusting total amount of sulphur containing compounds having at least one sulphur atom having an oxidation state below +6 in a metal or metal alloy plating bath,

• wherein the metal or metal alloy plating bath comprises one or more than one of said sulphur containing compounds and one or more than one reducing agent,
• the method comprising the steps:
• (a) obtaining from the metal or metal alloy plating bath a sample, and adding to the sample a known amount of an additional reducing agent to obtain a measuring sample, and, optionally diluting the sample prior to adding the additional reducing agent;
• (b) bringing the measuring sample obtained in step (a) into contact with a working electrode in a measuring unit and applying a constant potential to the working electrode such that both the one or more reducing agent and the additional reducing agent are anodically oxidized at the working electrode in the presence of the one or more than one said sulphur containing compounds to generate an anodic oxidation current, and simultaneously measuring the anodic oxidation current decaying over time to obtain current data of current values during the decaying;
• (c) optionally processing the current data of the measured anodic oxidation current obtained in step (b) to obtain processed current data,
• (d) determining a total amount of said sulphur containing compounds in said metal or metal alloy plating bath by comparing the current data obtained in step (b) or the processed current data obtained in step (c) with data or processed data, respectively, in a reference plot showing time specific anodic oxidation currents vs. corresponding known relative concentrations of said sulphur containing compounds in reference samples comprising reference total amounts of the sulphur containing compounds and an identical known amount of the reducing agents in the sample obtained in step (a),
• (e) based on the comparing in step (d), determining the total amount of said sulphur containing compounds in the measuring sample, and
• based on step (e), adjusting the total amount of said sulphur containing compounds in said metal or metal alloy plating bath to a desired level,
• wherein the anodic oxidation current decays in correlation with the total amount of said sulphur containing compounds both in the measuring sample and in the reference samples, and the anodic oxidation current of both the one or more reducing agent and the additional reducing agent are measured and not the oxidation current of said sulphur containing compounds.