A new in situ ultra-high vacuum (UHV) electrochemical cell containing a liquid electrolyte solution and Ti working electrode was designed and constructed to perform Rutherford backscattering spectrometry (RBS), under controlled electrochemical potentials. The depth resolution of RBS allowed for the determination of depth profiles for Ti, O, and other key transported species, in the electrode and in near-surface regions. Upon biasing the Ti electrode, subsequent RBS spectra releveled the time evolution of elemental depth profiles, characteristic of anodization, with Ti, O and Cl being mobile species. The differences between in situ and ex situ RBS measurements are emphasized. This work demonstrates the potential for in situ RBS to become a powerful tool for the investigation of a wide range of electrochemical processes including oxidation, electromigration, and deposition in batteries and other devices. (c) The Author(s) 2019. Published by ECS.