Hyphenation of electrochemistry and mass spectrometry is an attractive method to investigate oxidation and reduction processes. By using mass spectrometry, electrochemically generated products can be identified. In this Review, different approaches to electrochemistry–mass spectrometry will be summarized, including hyphenation of electrochemical flow cells to mass spectrometry as well as integration of separation steps between electrochemical reactions and detection of products. Fields of application range from bioanalytical studies to studies regarding corrosion, electrosynthesis and energy carriers. Important historical developments will be highlighted, followed by an overview of terminology and instrumental setups and discussion of developments within recent years (2017–2020).

No abstract

No abstract

The electrooxidation of thymine on screen-printed carbon electrodes was investigated utilizing different complementary instrumental approaches. The potential-dependent product profile was obtained by recording real-time mass voltammograms. Electrochemical flow cells with integrated disposable electrodes were directly coupled with mass spectrometry to facilitate a very fast detection of electrogenerated species. Thymine dimers were found at a potential of about 1.1 V in ammonium acetate (pH 7.0) and 1.25 V in ammonium hydrogen carbonate electrolyte (pH 8.0). Electrochemistry-capillary electrophoresis-mass spectrometry measurements revealed that two isobaric isomers of a dimeric oxidation product were formed. Separations at different time intervals between end of oxidation and start of separation showed that these were hydrated over time. An investigation of the pK a values by changing the separation conditions in electrochemistry-capillary electrophoresis-ultraviolet–visible spectroscopy measurements allowed for further characterization of the primary oxidation products. The results showed that both isomers exhibited two deprotonation steps. The oxidation products were further characterized by high-performance liquid chromatography-tandem mass spectrometry. Based on the obtained data, the main oxidation products of thymine in aqueous solution could most likely be identified as N(1)–C(5′) and N(1)–C(6′) linked dimer species evolving into the corresponding dimer hydrates over time. The presented methods for online characterization of electrochemically pretreated samples showed that not only mass spectrometric data can be obtained by electrochemistry-mass spectrometry but also further characterizations such as the investigation of product stability and the pH-dependent protonation or deprotonation behavior are possible. This is valid not only for stable oxidation products but also for intermediates, as analysis can be carried out within a short time scale. Thus, a vast amount of valuable experimental data can be acquired, which can help in understanding electrooxidation processes.

The characterization of the redox behavior of analytes is a very important aspect for many applications. Pure electrochemical approaches can provide useful information on electroactive species, but are of limited use regarding the identification of generated species. The hyphenation of electrochemistry and mass spectrometry (EC-MS) is a powerful method to investigate redox systems. In the present work, we show a simple approach to on-line EC-MS based on the application of electrochemical flow cells with implemented disposable electrodes. They are connected to electrospray ionization mass spectrometry (ESI-MS) via fused silica capillary tubing. The modularity of the flow cells offers a high flexibility of experimental setup and settings, so that a fast detection of oxidation or reduction products can be achieved. The usage of disposable electrodes guarantees a high level of quality assurance for EC-MS measurements.