The identification of new electrosynthetic pathways enables environmentally friendly synthetic applications. However, the development of miniaturized screening procedures/platforms to expedite the discovery of electrooxidation reactions remains challenging. Herein, we developed an integrated system that serves as a reactor and ion source in a single experimental step using only picomole-scale reactants to monitor electrooxidation in real-time. This reaction screening platform utilizes the intrinsic electrochemical capabilities of nano-electrospray ionization mass spectrometry. We validated the feasibility of this method by reproducing three known electrochemical reactions. We also discovered two new electroorganic reaction pathways: (i) C–N dehydrodimerization of 8-methyl-1,2,3,4-tetrahydroquinoline to construct a novel quinoline skeleton, and (ii) TEMPO-mediated accelerated electrooxidative dehydrogenation of tetrahydroisoquinolines. Moreover, the radical cations and key intermediates captured by this screening platform provided direct evidence for the mechanism of these novel electrochemical reactions.