Bookmark and Share

Voltammetry

About Voltammetry

3-Electrode CellVoltammetric methods of analysis involve the application of a potential (volts) in an electrochemical cell, and measuring the current (amps) that flows. Many different voltammetric techniques have been developed based on this current-voltage relationship, and have proven to be be extremely valuable tools for analyzing trace metals in solutions, determining complexation in organic and inorganic systems, studying kinetics and diffusion, among others.

One type of electrochemical cell used in voltammetry is the 3-electrode cell (see diagram at left). This cell consists of working, reference and counter electrodes. The potential is applied between the working and reference electrodes, and the current flow is measured between the working and counter electrodes. The working electrode provides the surface for electron transfer to occur for the system under investigation. For example, during cyclic voltammetry of a iron complex, the potential at the working electrode becomes more and more negative during the first part of the experiment. Essentially, no current flows until the potential of the working electrode becomes sufficiently negative to cause Fe3+ to be reduced to Fe2+.

Fe3+ + electron -› Fe2+

Applied PotentialWhen the reduction of Fe3+ begins to occur, the current flowing through the working/counter electrode pair increases. During the second part of the cyclic voltammetry experiment, the potential scan is reversed, causing the oxidation of the Fe2+ (that was generated during the initial potential sweep) back to Fe3+. Scanning the potential as a function of time, first in a negative direction, then in a positive direction, can be shown graphically (see diagram to right).

 

Voltammogram PlotA cyclic voltammogram consists of plotting the current that flows as a function of the applied potential. The trace on top [1] represents the reduction of Fe3+ to generate Fe2+. The trace on the bottom [2] represents the current that flows as the reverse reaction occurs (Fe2+ is oxidized to Fe3+).

Under the correct conditions, the amount of current that flows is related to the amount of the species present, making this a valuable quantitative technique.

Many types of electrodes can be used as the working electrode: dropping mercury, glassy carbon, gold, copper, platinum, etc., and the timing of the applied potential can be varied to extract a variety of information. Overall, voltammetry is a powerful analytical technique that can be applied in many situations.

BioAnalytical Systems Epsilon Electrochemical Workstation

Epsilon ElectrochemistryThe BAS Epsilon is a computer-interfaced electrochemical analyzer capable of many types of electrochemical measurements.

Cyclic Voltammetry/Linear Sweep Voltammetry
Chronoamperometry/Chronocoulometry
Controlled Potential Electrolysis
DC Potential Amperometry
Chronopotentiometry
Sampled Current Polarography
Normal Pulse Voltammetry/Polarography
Differential Pulse Voltammetry/Polarography
Square Wave Voltammetry
Stripping Voltammetric Techniques

Epsilon Cell StandBAS C-3 Cell Stand

The portion of the instrument where the actual electron transfer processes occur is in the electrochemical cell. The cell that we use is a 3-electrode cell consisting of reference, working and counter electrodes, with stirring and purging capabilities. The C-3 cell stand is interfaced to the potentiostat which, in turn, is interfaced to the PC.

Applications of Electrochemistry

The broad array of electrochemical techniques listed above has been applied to diverse areas of investigation. Below are listed a few examples of the application of electrochemical techniques in a variety of situations.

Characterization of transition metal complexes
Characterization of biosensors
Characterization of battery electrodes
Investigation of fuel cells
Investigation of corrosion and corrosion inhibitors
Corrosion behavior of surgical implant alloys
Development of microelectrodes to quantify neurotransmitters in synapses
Analysis of gunshot residue
Determination of metals in drinking water
Determination of trace levels of paraquat
Determination of carboplatin in serum
Determination of food colors in corks
Evaluation of natural oxide film on aluminum for food and drink containers
Evaluation of polymer coatings applied to aluminum food containers
Probing protein interactions by direct electrochemistry
Electrochemistry of semiconductors
Control of plating chemistry by voltammetric techniques