Electrochemical deposition-stripping analysis of molecules and proteins by online electrochemical flow cell/mass spectrometry

A methodology for online preconcentration of analytes and their subsequent electrochemically induced delivery to an online electrospray mass spectrometer is introduced. The approach is based on electrodeposition of an active metallic layer, silver deposit in this particular case, subsequent specific accumulation of the target analyte by electrochemical or chemical means onto the active layer, and finally oxidative electrostripping of the conductive layer along with the supported analyte to an online mass spectrometer. We demonstrate the new concept by selective electrochemical deposition of homocysteine and other organothiols directly on the working electrode of a miniature flow cell. The same approach was extended to the conjugation of the target analyte (avidin as a test case) to a thiolated ligand (biotin in this case) that was electrode-posited on the silver coated surface. Electrostripping of the silver dissolves the target species and allows their delivery to an online ESI-MS. Furthermore, the dissolved silver ions promote ionization, and its characteristic isotopic pattern assists in the identification of the target analyte.