[electro- + Gr. hodos, a way]

1. An electrical terminal or lead.
2. A conductive medium.
3. In electrotherapy, an instrument with a point or surface from which to discharge current to a patient's body.
4. An electrical terminal or lead that is adapted to sense current or voltage in response to specific analytes, for purposes of quantifying the particular analyte.

active electrode

An electrode that is smaller than a dispersive electrode and produces stimulation in a concentrated area.

calomel electrode

An electrode that develops a standard electric potential and is used to provide a reference voltage in the circuit for sensing electrodes. It is composed of an amalgam of mercury and mercury (I) chloride. It is used as a standard in determining the pH of fluids.

carbon dioxide electrode

A blood gas electrode used to measure the carbon dioxide tension (symbol Pco2) in blood. Its operation is based on the diffusion of carbon dioxide from the blood sample through a semipermeable membrane into a buffer solution with a subsequent change in the pH of the buffer.
SYN: SEE: Severinghaus electrode

Clark electrode

SEE: Oxygen electrode.

coated wire electrode

ABBR: CWE A chemical sensor in some clinical laboratory analyzers that functions similarly to a pH electrode.
SEE: hydrogen electrode; SEE: saturated calomel electrode

depolarizing electrode

An electrode with greater resistance than the part of the body in the circuit.

depth electrode

A monitoring electrode implanted into tissue, e.g., into the brain or spinal cord.

dispersive electrode

SEE: Indifferent electrode.

fetal scalp electrode

ABBR: FSE A device to measure the health of the fetus during complicated or protracted labor and delivery.

gas-sensing electrode

An electrode in which a gas-permeable membrane separates the test solution fluid from an aqueous electrode solution in contact with an ion-selective electrode. Gas permeation of the membrane changes the chemical equilibrium within the electrolyte, and the ion-sensitive electrode detects this change.

glass electrode

In chemistry, a chemical sensor that uses a glass membrane as the sensing surface, as opposed to one that uses an organic or solid-state membrane. The glass contains materials in its structure that are sensitive to a material that is to be measured. In the case of a pH glass electrode, lithium ions are commonly used.

hydrogen electrode

An electrode that absorbs and measures hydrogen gas; used as the reference for pH measurement in research laboratories.

immobilized enzyme electrode

A chemical sensor that is highly selective due to a specific enzyme incorporated into its structure.

indifferent electrode

An electrode larger than an active electrode. It produces electrical stimulation over a large area.
SYN: SEE: dispersive electrode

internal reference electrode

The metal electrode inside all chemical-sensing potentiometric electrodes. The two most common internal reference electrodes are the calomel and the silver/silver chloride.

ion-selective electrode

A chemical transducer that yields a response to variations in the concentration of a given ion in solution.

liquid membrane electrode

An electrode in which the sensing membrane is made up of a hydrophobic ion-exchange neutral carrier (ionophore) dissolved in a viscous, water-insoluble solvent. The liquid membrane is physically supported by an inert porous matrix such as cellulose acetate.

multiple point electrode

Several sets of terminals providing for the use of several electrodes.
SEE: multiterminal

negative electrode

A cathode; the pole by which electric current leaves the generating source.

oxygen electrode

An electrode used to measure the partial pressure of oxygen (Po2) or the blood glucose concentration of a fluid sample.
SYN: SEE: Clark electrode; SEE: Po2 electrode; SEE: polarographic electrode

PO2 electrode

SEE: Oxygen electrode.

point electrode

An electrode with an insulating handle at one end and a small metallic terminal at the other for use in applying static sparks.

polarographic electrode

SEE: Oxygen electrode.

polymer membrane electrode

An electrode in which the sensing membrane is an organic polymer containing a hydrophobic ion-exchange neutral carrier (ionophore).

positive electrode

An anode; the pole opposite a cathode.

reference electrode

A chemical electrode whose cell potential remains fixed and against which an indicator electrode is compared. The most common reference electrode is the silver/silver chloride (Ag/AgCl) electrode.

saturated calomel electrode

ABBR: SCE One of two practical reference electrodes, used with a mercurous chloride (calomel) paste in pH and other potentiometric instruments. The other is the silver/silver chloride electrode. The calomel electrode has been the standard secondary reference electrode used in the laboratory since the introduction of the pH electrode.

Severinghaus electrode

SEE: Carbon dioxide electrode.

solid-state membrane electrode

An electrode in which the sensing membrane is made of a single crystal or pressed pellet containing the salt of the ion to be sensed.

standard hydrogen electrode

ABBR: SHE The standard reference electrode against which all others are measured. Its assigned electrode potential is 0.000 V.

subcutaneous electrode

An electrode placed beneath the skin.

surface electrode

An electrode placed on the surface of the skin or exposed organ.

therapeutic electrode

An electrode used for introduction of medicines through the skin by ionization.
SEE: iontophoresis