Scanning Electrochemical Cell Microscopy for Sub-Micrometer Mass Spectrometric Studies of Electrochemical Reactions.

Nanoscale electrochemistry has been significantly advanced through the utilization of nanopipettes, enabling precise electrode area confinement and localized measurements. In particular, scanning electrochemical cell microscopy (SECCM) has leveraged the use of nanopipettes to facilitate measurement of electrochemical processes with high spatiotemporal resolution. While nano electrochemistry is well-suited to study processes at the sub-micrometer level, there is a need for complementary analytical techniques that can enable the detection of intermediates and help to elucidate reaction pathways that occur in the small volumes. In this work, we demonstrate the coupling of SECCM with MS for the detection of reaction products formed by the oxidation of uric acid. Specifically, species generated at the tip of an SECCM probe could be delivered to a mass spectrometer via nanoelectrospray ionization and exhibit both stable ion signal and high sensitivity. We demonstrate that this workflow enables the detection of analytes generated from SECCM probes of 3 μm and 900 nm tip diameter, despite the low conversion ratio associated with the smaller nanopipette diameters. Results presented herein demonstrate the SECCM-MS workflow as a powerful approach to detect low-abundance species formed from micro- and nanoscale electrochemical reactions.