The anodic oxidation stability of battery components like the conductive carbon black (Super C65) and the co-solvent ethylene carbonate (EC) is of great relevance, especially with regards to high-voltage cathode materials. In this study, we use On-line Electrochemical Mass Spectrometry (GEMS) to deconvolute the CO and CO2 evolution from the anodic oxidation of carbon and electrolyte by using a fully C-13-isotope labeled electrolyte based on ethylene carbonate with 2 M LiClO4. We present a newly developed two-compartment cell, which provides a tight seal between anode and cathode compartment via a solid Li+-ion conducting separator, and which thus allows us to examine the effect of trace amounts of water on the anodic oxidation of carbon (C-12) and ethylene carbonate (C-13) at high potentials (> 4.5 V) and 10 to 60 degrees C. Moreover, we report on the temperature dependence of the water-driven hydrolysis of ethylene carbonate accompanied by CO2 evolution. Finally, by quantifying the evolution rates of (CO)-C-12/(CO2)-C-12 and (CO)-C-13/(CO2)-C-13 at 5.0 V, we demonstrate that the anodic oxidation of carbon and electrolyte can be-substantial, especially at high temperature and in the presence of trace water, posing significant challenges for the implementation of 5 V cathode materials. (C) The Author(s) 2015. Published by ECS. All rights reserved.