Investigation of the Electrooxidation of Thymine on Screen-Printed Carbon Electrodes by Hyphenation of Electrochemistry and Mass Spectrometry

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.

Accelerating Electrochemical Reactions in a Voltage‐Controlled Interfacial Microreactor

“…ESI can be coupled with a separate electrochemical (EC) flow reactor [14] or directly used as an electrochemical cell [3c, 15] for various studies such as identification of reaction intermediates, [14d-f] examination of electrochemical reactions, [14a, 15b] and to mimic biologically relevant electrochemical reactions. [16] However, the electrochemical reactions occurring in such electrochemical cells or ESI emitters reflect the reaction behavior in the bulk phase and do not possess the acceleration phenomenon. Molecules that are easy to oxidize or reduce by one-electron transfer can quickly form a predictable species in the ESI process and the scope of such reactions is very limited.…”

Electrochemical Sensor Nanoarchitectonics for Sensitive Detection of Uric Acid in Human Whole Blood Based on Screen-Printed Carbon Electrode Equipped with Vertically-Ordered Mesoporous Silica-Nanochannel Film

“…As an organic combination of carbon electrode and screen-printed electrode, screen-printed carbon electrodes (SPCEs) have unique characteristics including high chemical stability, wide potential window, good biocompatibility, low cost, easy mass production, and disposable use [ 13 , 14 , 15 ]. However, it was proven that VMSF cannot be stably grown on carbon electrodes.…”

“…Compared with conventional solid electrodes (e.g., glassy carbon electrode-GCE, Au or Pt electrode), screen-printed electrodes (SPEs) have attracted much attention owing to their low cost, easy batch fabrication, convenient array and flexible design, and possibility of low sample consumption [ 10 , 11 , 12 ]. Amongst alternatives, screen-printed carbon electrodes (SPCEs) have great potential in the detection of biomarkers in clinical samples owing to the merits of a wide potential window, low background current, high biocompatibility, and excellent chemical stability [ 13 , 14 , 15 ]. However, modification of electrode surfaces to improve the anti-interference ability and sensitivity are urgently needed for direct analysis of complex samples with high performance.…”

Recent Advances of In‐Source Electrochemical Mass Spectrometry

“…The combination of electrochemistry (EC) and mass spectrometry (MS) has become a powerful and versatile strategy that allows one to characterize a broad range of electrochemical and biological reactions, and extends the scope of analytes for mass spectrometric analysis. [1][2][3][4][5][6][7][8][9][10][11][12] In this hyphenation, MS has often been used due to its high sensitivity and specificity for determination of electrochemical reactions, providing structural information unavailable from EC methods. Electrochemical reactions can be used to oxidize or reduce analytes so as to improve the ionization of analytes for mass spectrometric analysis.…”