Development of better catalysts for the oxygen reduction reaction (ORR) and other electrocatalytic processes requires detailed knowledge of reaction pathways and intermediate species. Here we report a new methodology for detecting charged reactive intermediates and its application to the mechanistic analysis of ORR. A nanopipette filled with an organic phase that is immiscible with the external aqueous solution was used as a tip in the scanning electrochemical microscope to detect and identify a short-lived superoxide (O-2(center dot-)) intermediate and to determine the rate of its generation at the catalytic Pt substrate and its lifetime in neutral aqueous solution. The voltammogram of the O-2(center dot-) anion transfer to the organic phase provides a unique signature for unambiguous identification of superoxide. The extremely short attainable separation distance between the pipette tip and substrate surface (similar to 1 nm) makes this technique suitable for detecting and identifying charged intermediates of catalytic processes with a lifetime of a few nanoseconds.