On-column electrochemical reactions accompanying the electrospray process

It is well-established that electrochemical reactions can occur within the capillary of an electrospray (ES) devise coupled to a mass spectrometer. In fact, such reactions must occur to maintain charge balance during the ES process. However, electrochemical reactions occurring distal to the capillary as a result of the high potential applied to the capillary have not been thoroughly investigated. In the present communication, we show that electrochemical processes can occur on a high performance liquid chromatography (HPLC) column coupled to an ES capillary. On-column solvent electrolysis is proposed to generate free radicals, which can subsequently initiate analyte oxidation. Oxidation of steroid sulfates possessing a reactive double bond between C-5 and C-6 is demonstrated. The possibility of similar reactions occurring within peptides possessing a site of unsaturation is also considered.