Self-assembled monolayers of dodecanethiol on gold electrodes were characterized in an ionic liquid 1-butyl-4-methylimidazolium tetrafluoroborate (BMIMBF4) containing redox probes ferrocene (Fc)/ferrocenium (Fc(+)) or others. An irreversible redox reaction of Fc/Fc(+) has been observed. The results may indicate a special double layer structure of an electrode/electrolyte interface and an interaction of imidazolium and Fc. Coverage of the monolayer has been determined by stripping voltammetry in BMIMBF4. (c) 2010 The Electrochemical Society. [DOI: 10.1149/1.3509769] All rights reserved.