By coupling an electrochemical flow-cell to electrospray mass spectrometry (ESI-MS), a very powerful tool for studies of electrochemical reactions as well as for analyses of electroactive compounds can be obtained. With ESI-MS [1] it is possible to identify and quantitate electrochemically produced oxidation and reduction products and by coupling electrochemistry to ESI-MS it also becomes possible to utilise electrochemical reactions for the preconcentration, ionisation and tagging [2] of selected analytes prior to ESI-MS. The combined approach is, however, complicated by the need to decouple the electrochemical cell from the ESI-MS high voltage and the fact that the electrospray process itself involves electrochemical reactions [1]. Care also needs to be taken to ensure that the electrochemically generated products do not undergo unwanted redox reactions during their transfer to the mass spectrometer [3]. To enable the detection of unstable products it is likewise important to minimise the transfer time between the electrochemical cell and the mass spectrometer. In the present communication, on- and off-chip couplings of electrochemistry to ESI-MS will be discussed with a particular emphasis on the design of the electrochemical flow-cell. It will be demonstrated that the approach can be used to identify electrochemically produced reaction products and that electrochemical ionisation can be used to facilitate studies of compounds immobilised on surfaces. The influence of the design of the electrochemical cell and the flow system in general on the possibilities to detect an electrochemically generated species will also be discussed. A PDMS based device [4] allowing an on-chip coupling of an electrochemical cell to ESI-MS with a subsecond transfer time will likewise be described.

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1. Electrochemical Sample Pretreatment and Detection Techniques for Lab-on-a-Chip Applications