From studying five batches of the same IL ([MPPip][TFSI]) from two suppliers and different purchase dates, we observed two distinctly different electrochemical behaviours in the CVs recorded on Au(111). This result does not rule out that other batches from the same or even other suppliers might behave differently. We suggest that impurities are at the origin of the observed differences, which can contribute in different ways to the electrochemical behaviour of the system. First, the impurities themselves can adsorb on the surface, thus taking part in the adlayer formation on the surface, which can result in additional peaks in the CV (when the process involves a charge transfer process). Secondly, the impurities could also be continuously converted catalytically, which results in a current that adds to the currents related to the surface redox process of adlayer formation. We assume that a combination of both effects takes place on the electrode surface, since (i) we observe different peaks in both behaviours and (ii) based on our evaluation of the charges passed in regions with negative or positive currents, it is clear that the observed current densities are not only related to surface ad-and desorption processes (the total charges exceed those of monolayer adsorbate layer formation).