Microfluidic Electrochemistry Meets Trapped Ion Mobility Spectrometry and High-Resolution Mass Spectrometry-In Situ Generation, Separation, and Detection of Isomeric Conjugates of Paracetamol and Ethoxyquin.

Over the last 3 decades, electrochemistry (EC) has been successfully applied in phase I and phase II metabolism simulation studies. The electrochemically generated phase I metabolite-like oxidation products can react with selected reagents to form phase II conjugates. During conjugate formation, the generation of isomeric compounds is possible. Such isomeric conjugates are often separated by high-performance liquid chromatography (HPLC). Here, we demonstrate a powerful approach that combines EC with ion mobility spectrometry to separate possible isomeric conjugates. In detail, we present the hyphenation of a microfluidic electrochemical chip with an integrated mixer coupled online to trapped ion mobility spectrometry (TIMS) and time-of-flight high-resolution mass spectrometry (ToF-HRMS), briefly chipEC-TIMS-ToF-HRMS. This novel method achieves results in several minutes, which is much faster than traditional separation approaches like HPLC, and was applied to the drug paracetamol and the controversial feed preservative ethoxyquin. The analytes were oxidized in situ in the electrochemical microfluidic chip under formation of reactive intermediates and mixed with different thiol-containing reagents to form conjugates. These were analyzed by TIMS-ToF-HRMS to identify possible isomers. It was observed that the oxidation products of both paracetamol and ethoxyquin form two isomeric conjugates, which are characterized by different ion mobilities, with each reagent. Therefore, using this hyphenated technique, it is possible to not only form reactive oxidation products and their conjugates in situ but also separate and detect these isomeric conjugates within only a few minutes.

Spectroelectrochemistry, the future of visualizing electrode processes by hyphenating electrochemistry with spectroscopic techniques.

The combination of electrochemistry and spectroscopy, known as spectroelectrochemistry (SEC), is an already established approach. By combining these two techniques, the relevance of the data obtained is greater than what it would be when using them independently. A number of review papers have been published on this subject, mostly written for experts in the field and focused on recent advances. In this review, written for both the novice in the field and the more experienced reader, the focus is not on the past but on the future. The scope is narrowed down to four techniques the authors claim to have the most potential for the future, namely: infrared spectroelectrochemistry (IR-SEC), Raman spectroelectrochemistry (Raman-SEC), nuclear magnetic resonance spectroelectrochemistry (NMR-SEC) and, perhaps slightly more controversial but certainly promising, electrochemistry mass-spectrometry (EC-MS).