On the Coupling of Electrochemical Cells to Electrospray Ionisation Mass Spectrometry

The coupling of an electrochemical cell to electrospray ionisation mass spectrometry (ESI-MS) provides a powerful tool both when analysing electrochemically active compounds (which then may be preconcentrated and/or ionised electrochemically) and when studying electrochemical reactions in general. The fact that electrochemical reactions have been demonstrated 1 to be of fundamental importance in electrospray ionisation mass spectrometry (ESI-MS) may, however, complicate the coupling of electrochemical cells to ESI-MS and the interpretation of the obtained mass spectra. It is well-known that the electrochemical reactions taking place on the electrospray electrode (commonly a metal capillary or a metal coated fused silica emitter) may alter the composition (e.g. the pH) of the solution electrosprayed. This can, for instance, alter the mass spectrometric sensitivity for analytes such as peptides and proteins. Changes in the mass spectra may also be observed as a result of electrochemical reactions involving the analytes of interest and/or the electrospray emitter (corrosion of metal coated fused silica emitters have been found to be a significant problem in positive ESI-MS) 2 . Electrochemical reactions can, on the other hand, also be used for the ionisation of analytes as well as for tagging purposes 3 based on redox reactions taking place either in the spray or in an upstream electrochemical cell. In the present communication, a novel set-up for the coupling of a commercially available thin layer electrochemical flow cell to electrospray mass spectrometry is described. By the use of this set-up, it is possible to minimise interferences due to the electrochemical reactions occurring on the thin layer cell counter electrode. The electrochemical reactions in the electrospray itself and the possible effects of such reactions on the appearance of mass spectra will also be discussed as well as different approaches to decouple the electrochemical cell from the electrospray high voltage. References