A technique has been developed for the study of reaction mechanism and the monitoring of copper electroplating baths utilizing a combination of solid phase extraction (SPE) and high-performance liquid chromatography (HPLC). This method appears suitable for live plating bath control as well as for organic identification, concentration measurement, and reaction mechanism studies. While in the past the total amount of carbon (TOC) present in the deposition bath was used to quantify the decomposition of organics and to determine the plating bath quality, a strong correlation between the TOC measurement and effective plating bath composition was not possible. Moreover, a direct way to thoroughly analyze the organic components of the bath is not commonly available using current electrochemical techniques. However, the results from experiments conducted with the technique described in this paper show how the monitoring of a few diagnostic peaks recovered from a live bath sample can be used directly for this purpose. The identification and quantification of by-products is also proven. Two copper sulfuric plating baths at different acidity were used for this study, and the stability of bis(sodiumsulfopropyl) disulfide and polyethylene glycol additive components, as well as their degradation mechanism and by-products, are studied in this work. (c) 2005 The Electrochemical Society. All rights reserved.