EC-MS can be used to analyze a wide range of biological reaction. In this technique, electrochemistry is used to determine the concentration or chemical reactivity of a substance by measuring either the potential, charge, or current. Mass spectrometry is then applied to further characterize these analytes.
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What is electrochemistry mass spectrometry?
Fundamentals of electrochemistry
Electrochemistry (EC) is the study of the movement of electrons in an oxidation-reduction reaction. To achieve reliable results with EC, the behavior and properties of electrodes and redox reactions must be considered. An electrochemical cell that contains at least two electrodes is typically used, as well as four interfacial electrochemical techniques; potentiometry, coulometry, amperometry, and voltammetry.
Differential Electrochemical Mass Spectrometry (DEMS)
Electrochemistry coupled with mass spectrometry (EC/MS) is used to study various electrochemical reactions. Differential electrochemical mass spectrometry (DEMS) combines electrochemical half-cell experimentation with mass spectrometry.
DEMS was developed using mass spectrometry (MS) to detect gaseous products generated in an electrochemical cell containing perchloric acid. The gaseous products were selectively transferred from the electrochemical cell into the MS system using a hydrophobic membrane connected to a porous electrode. This method has shorter response times that detects reaction products during cyclic voltammetry.
During DEMS, the ion current of a species involved in the electrochemical reaction is measured, and the intensity is plotted against the electrochemical potential.
DEMS instrumentation
The MS components of DEMS mostly use electron ionization (EI). The vacuum system consists of at least two, individually pumped vacuum chambers connected by an aperture or skimmer.
The EC components are separated from the MS components by a hydrophobic membrane that prevents the transfer of electrolytes into the mass spectrometer. The porous membranes are usually made from polytetrafluoroethylene or ethylene-tetrafluoroethylene copolymer that are durable and chemical resistant.
The applications of electrochemistry mass spectrometry
EC/MS is very versatile and has provided detailed information and insightful discoveries, such as mimicking metabolic pathways and tagging of protein/peptide thiol groups to enhance MS signals.
Studying the mechanism of oxygen reduction at a water/oil interface
Electrochemical reactions at a liquid-liquid interface are studied using cyclic voltammetry spectroscopy. MS can detect the products and intermediates generated during the electrochemical process using their molecular weight. EC/MS has been used to study oxygen reduction at the water/oil interface and has allowed for a mechanism of the oxygen reduction to be proposed.
Using diamond nanowires with EC/MS
EC/MS can be used with diamond nanowires to increase the versatility of EC/MS techniques. This method places a Teflon membrane between the porous electrode and the mass spectrometer ionization chamber, so the reaction products can be ionized by electron impact without the interference of the solvent. Other methods of ionization include thermo-spray, fast atom bombardment, chemical ionization, and electrospray ionization.
Analyzing 3D protein structures
MS combined with EC and isotope labeling strategies are used to analyze 3D protein structures and conformational changes. The target protein/protein complex is digested, electrochemically reduced, and then MS is performed. This identifies crosslinks containing disulfide bonds. The electroreduction during this analysis converts cross-links into peptides allowing for tandem mass spectrometry to be performed.
Further Reading