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Related Concept Videos

Potentiometry: Overview01:06

Potentiometry: Overview

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Potentiometry is an analytical technique that measures the potential difference between two electrodes in an electrochemical cell without drawing any significant current that could alter the solution's composition. This method employs an indicator electrode, which exchanges electrons with the analyte solution, and a reference electrode with a constant potential. Each electrode is immersed in a solution comprised of two half-cells. In a conventional setup, the reference electrode serves as...
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Controlled-Potential Coulometry: Electrolytic Methods01:17

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Controlled-potential coulometry, also known as potentiostatic coulometry, employs a three-electrode system in which the working electrode's potential is precisely regulated using a potentiostat. Platinum working electrodes are utilized for positive potentials, while mercury pool electrodes are favored for extremely negative potentials. The platinum counter electrode is separated from the analyte using a membrane or salt bridge to avoid interference in the analysis.
The chosen potential...
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Potentiometry: Membrane Electrodes01:15

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Membrane electrodes, also known as p-ion electrodes, use membranes that selectively interact with free analyte ions, generating a potential difference across the membrane. The resulting membrane potential, known as the asymmetry potential, is not zero even when analyte concentrations on both sides of the membrane are equal. The membrane's response is typically not selective to a single analyte but proportional to the concentration of all ions in the sample solution capable of interacting at...
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Introduction to Enzyme Kinetics01:19

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Enzyme kinetics studies the rates of biochemical reactions. Scientists monitor the reaction rates for a particular enzymatic reaction at various substrate concentrations. Additional trials with inhibitors or other molecules that affect the reaction rate may also be performed.
The experimenter can then plot the initial reaction rate or velocity (Vo) of a given trial against the substrate concentration ([S]) to obtain a graph of the reaction properties. For many enzymatic reactions involving a...
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Potentiometry: Types of Electrodes01:19

Potentiometry: Types of Electrodes

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Reference electrodes serve as a stable reference point for potentiometric measurements, while indicator and working electrodes react to variations in the composition of a solution.
The Standard Hydrogen Electrode (SHE) is a widely used reference electrode that maintains zero potential across all temperatures. However, its need for a continuous hydrogen gas supply renders it impractical for everyday use.
An alternative to SHE is the Saturated Calomel Electrode (SCE). This electrode features an...
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Controlled-Current Coulometry: Overview01:27

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Controlled current coulometry, also known as amperostatic coulometry, is a technique used in electrochemical analysis to measure the quantity of a substance through the controlled passage of current. It involves the application of a constant current to an electrochemical cell containing the analyte of interest. As the current flows through the cell, the analyte undergoes a redox reaction at the electrode surface, resulting in a charge transfer. By monitoring the time required for a certain...
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Enzyme Kinetics via Open Circuit Potentiometry.

Lettie A Smith1, Matthew W Glasscott1, Kathryn J Vannoy1

  • 1Department of Chemistry , The University of North Carolina at Chapel Hill , Chapel Hill , North Carolina 27599 , United States.

Analytical Chemistry
|December 14, 2019
PubMed
Summary

Open circuit potentiometry (OCP) measures enzyme turnover kinetics (k_turn) using redox mediators. This method, demonstrated with glucose oxidase, offers a size-independent alternative to amperometry for biosensor development.

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Area of Science:

  • Electrochemistry
  • Enzyme kinetics
  • Biosensor technology

Background:

  • Enzyme turnover kinetics (k_turn) are crucial for understanding enzyme function and developing biosensors.
  • Traditional methods like amperometry can be limited by electrode size and mass transfer effects.
  • Open circuit potentiometry (OCP) offers a potential alternative for kinetic measurements.

Purpose of the Study:

  • To demonstrate the application of open circuit potentiometry (OCP) for measuring enzyme turnover kinetics (k_turn).
  • To develop a theoretical model correlating OCP signals with enzymatic rate expressions.
  • To compare OCP with amperometry for kinetic analysis and explore mediator effects on k_turn.

Main Methods:

  • Utilized open circuit potentiometry (OCP) with a ferrocenemethanol/ferrocenium methanol (FcMeOH/FcMeOH+) redox mediator system.
  • Employed glucose oxidase as a model enzyme to study electron transfer with the mediator.
  • Developed a theoretical model integrating enzymatic kinetics into the Nernst equation to interpret potential transients.

Main Results:

  • OCP successfully measured enzyme turnover kinetics (k_turn), with experimental data fitting the derived theoretical model.
  • Amperometry on ultramicroelectrodes (UMEs) yielded similar kinetic information but is subject to electrode size and mass transfer limitations.
  • Demonstrated that OCP is independent of electrode size and mass transfer effects, offering a distinct advantage.

Conclusions:

  • Open circuit potentiometry (OCP) is a viable and robust method for determining enzyme turnover kinetics (k_turn).
  • The developed theoretical framework accurately explains potentiometric transients during enzymatic redox mediation.
  • OCP presents a promising, size-independent approach for biosensor applications, potentially overcoming electrode fouling issues.