Dropping mercury electrode
Encyclopedia
The dropping mercury electrode (DME) is a working electrode
made of mercury
and used in polarography
. Experiments run with mercury electrodes are referred to as forms of polarography
even if the experiments are identical or very similar to a corresponding voltammetry
experiment which use solid working electrodes. Like other working electrodes these electrodes are used in electrochemical studies using three electrode systems
when investigating reaction mechanisms
related to redox
chemistry among other chemical
phenomena.
passes through an insulating capillary
producing a droplet which grows from the end of the capillary in reproducible way. Each droplet grows until it reaches a diameter of about a millimeter and releases. The released droplet is no longer in contact with the working electrode
whose contact is above the capillary. As the electrode is used mercury collects in the bottom of the cell. In some cell designs this mercury pool is connected to a lead and used as the cell's auxiliary electrode
. Each released drop is immediately followed by the formation of another drop. The drops are generally produced at a rate of about 0.2 Hz.
. These changing current effects combined with experiments where the potential is continuously changed can result in noisy traces. In some experiments the traces are continually sampled, showing all the current deviation resulting from the drop growth. Other sampling methods smooth the data by sampling the current at the electrode only once per drop at a specific size. The DME's periodic expansion into the solution and hemispherical shape also effect the way anaylte diffuses to the electrode surface.
Working electrode
The working electrode is the electrode in an electrochemical system on which the reaction of interest is occurring. The working electrode is often used in conjunction with an auxiliary electrode, and a reference electrode in a three electrode system...
made of mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
and used in polarography
Polarography
Polarography is a subclass of voltammetry where the working electrode is a dropping mercury electrode or a static mercury drop electrode ., useful for its wide cathodic range and renewable surface...
. Experiments run with mercury electrodes are referred to as forms of polarography
Polarography
Polarography is a subclass of voltammetry where the working electrode is a dropping mercury electrode or a static mercury drop electrode ., useful for its wide cathodic range and renewable surface...
even if the experiments are identical or very similar to a corresponding voltammetry
Voltammetry
Voltammetry is a category of electroanalytical methods used in analytical chemistry and various industrial processes. In voltammetry, information about an analyte is obtained by measuring the current as the potential is varied.- Three electrode system :...
experiment which use solid working electrodes. Like other working electrodes these electrodes are used in electrochemical studies using three electrode systems
Potentiostat
A potentiostat is the electronic hardware required to control a three electrode cell and run most electroanalytical experiments. A Bipotentiostat and polypotentiostat are potentiostats capable of controlling two working electrodes and more than two working electrodes, respectively.The system...
when investigating reaction mechanisms
Electrochemical reaction mechanism
In chemistry, an electrochemical reaction mechanism is the step by step sequence of elementary steps, involving at least one outer sphere electron transfer, by which an overall chemical change occurs .- Overview :...
related to redox
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
chemistry among other chemical
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
phenomena.
Structure
A flow of mercuryMercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
passes through an insulating capillary
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
producing a droplet which grows from the end of the capillary in reproducible way. Each droplet grows until it reaches a diameter of about a millimeter and releases. The released droplet is no longer in contact with the working electrode
Working electrode
The working electrode is the electrode in an electrochemical system on which the reaction of interest is occurring. The working electrode is often used in conjunction with an auxiliary electrode, and a reference electrode in a three electrode system...
whose contact is above the capillary. As the electrode is used mercury collects in the bottom of the cell. In some cell designs this mercury pool is connected to a lead and used as the cell's auxiliary electrode
Auxiliary electrode
The Auxiliary electrode, often also called the counter electrode, is an electrode used in a three electrode electrochemical cell for voltammetric analysis or other reactions in which an electrical current is expected to flow...
. Each released drop is immediately followed by the formation of another drop. The drops are generally produced at a rate of about 0.2 Hz.
Considerations
A major advantage of the DME is that each drop has a smooth and uncontaminated surface free from any adsorbed analyte or impurity. The self-renewing electrode does not need to be cleaned or polished like solid electrode. This advantage comes at the cost of a working electrode with a constantly changing surface area. Since the drops are produced predictably the changing surface area can be accounted for or even used advantageously. In addition the drops growth causes capacitive current and faradaic currentFaradaic current
The faradaic current is the current generated by the reduction or oxidation of some chemical substance at an electrode. The net faradaic current is the algebraic sum of all the faradaic currents flowing through an indicator electrode or working electrode....
. These changing current effects combined with experiments where the potential is continuously changed can result in noisy traces. In some experiments the traces are continually sampled, showing all the current deviation resulting from the drop growth. Other sampling methods smooth the data by sampling the current at the electrode only once per drop at a specific size. The DME's periodic expansion into the solution and hemispherical shape also effect the way anaylte diffuses to the electrode surface.
See also
- working electrodeWorking electrodeThe working electrode is the electrode in an electrochemical system on which the reaction of interest is occurring. The working electrode is often used in conjunction with an auxiliary electrode, and a reference electrode in a three electrode system...
- voltammetryVoltammetryVoltammetry is a category of electroanalytical methods used in analytical chemistry and various industrial processes. In voltammetry, information about an analyte is obtained by measuring the current as the potential is varied.- Three electrode system :...
- polarographyPolarographyPolarography is a subclass of voltammetry where the working electrode is a dropping mercury electrode or a static mercury drop electrode ., useful for its wide cathodic range and renewable surface...
- hanging mercury drop electrodeHanging mercury drop electrodeThe hanging mercury drop electrode is a working electrode variation on the dropping mercury electrode . Experiments run with dropping mercury electrodes are referred to as forms of polarography...