Organic addition agents in copper plating baths are monitored by diluting a sample of the bath with sulfuric acid and hydrochloric acid and optionally a cupric salt. The diluting provides a bath having conventional concentrations of cupric ion, sulfuric acid and hydrochloric acid; and adjusted concentrations of the organic addition agents of 1/X of their original values in the sample; where X is the dilution factor. CVS techniques are used to determine concentrations of organic addition agents.