Over the last decades ionic liquids (ILs) received an increasing interest in various research areas such as chemical synthesis, analytical chemistry, biology, and electrochemistry. However, possible contaminations natively present in the IL can significantly impact their properties as well as the interpretation of their bahavior. Methods for assessing the quality of ILs have been suggested, e.g. nuclear magnetic resonance (NMR) spectroscopy for detecting organic solvents in the IL, which are, however, rarely performed prior to their use in experiments or applications. In this work, we present surface science and electrochemical techniques to explore possible qualitative differences between different batches of the same IL from different suppliers purified by various pretreatments.