electrode

1. Device to record one of the two extremities of an electric circuit; one of the two poles of an electric battery or of the end of the conductors connected thereto. 2. An electrical terminal specialized for a particular electrochemical reaction. [electro- + G. hodos, way]

- active e. a small e. whose exciting effect is used to stimulate or record potentials from a localized area. SYN: exciting e., localizing e., therapeutic e..

- calomel e. an e. in which the wire is connected through a pool of mercury to a paste of mercurous chloride (Hg₂Cl₂, calomel) in a potassium chloride solution covered by more potassium chloride solution; commonly used as a reference e..

- carbon dioxide e. a glass e. in a film of bicarbonate solution covered by a thin plastic membrane permeable to carbon dioxide but impermeable to water and electrolytes; the carbon dioxide pressure of a gas or liquid sample quickly equilibrates through the membrane and is measured in terms of the resulting pH of the bicarbonate solution, as sensed by the glass e.; commonly used to analyze arterial blood samples for CO₂. SYN: Severinghaus e..

- central terminal e. in electrocardiography, an e. in which connections from the three limbs (right arm, left arm, and left leg) are joined and led to the electrocardiograph to form the indifferent e., theoretically at zero potential for the system.

- Clark e. an oxygen e. consisting of the tip of a platinum wire exposed to a thin film of electrolyte covered by a plastic membrane permeable to oxygen but not to water or the electrolyte. When a certain voltage is applied, oxygen is destroyed at the platinum surface; the flow of current is then proportional to the rate at which oxygen can diffuse to the platinum surface from the gas or liquid sample outside the membrane and is thus a measure of the oxygen pressure in the sample; commonly used to measure oxygen pressure in arterial blood samples.

- dispersing e. SYN: indifferent e..

- exciting e. SYN: active e..

- exploring e. an e. placed on or near an excitable tissue; in unipolar electrocardiography, the e. is placed on the chest in the region of the heart and paired with an indifferent e..

- glass e. a thin-walled glass bulb containing a standard buffer solution, quinhydrone, and a platinum wire; when immersed in an unknown solution, a potential difference develops that varies with the pH of the unknown solution; this difference can be made to give the pH; used in pH meters.

- hydrogen e. the ultimate standard of reference in all pH determinations, limited and technically difficult to use, consisting of a piece of spongy platinum black partly immersed in a solution in a small glass tube; the tube above the solution is filled with hydrogen gas that is bubbled through the solution and absorbed by the platinum; the e. thus measures the potential between H₂ and H⁺, the “standard” potential of which (1 atmosphere, 1 molar) is taken as zero; hence, the hydrogen e. potential measures [H⁺] or pH.

- indifferent e. in unipolar electrocardiography, a remote e. placed either upon a single limb or connected with the central terminal and paired with an exploring e.; the indifferent e. is supposed to contribute little or nothing to the resulting record. SYN: dispersing e., silent e..

- ion-selective electrodes glass, liquid ion-exchange, or solid state electrodes used to measure electrolyte and calcium ion activity in biological fluids.

- localizing e. SYN: active e..

- negative e. SYN: cathode.

- oxidation-reduction e. an e. capable of measuring oxidation-reduction potential. See quinhydrone e.. SYN: redox e..

- oxygen e. an e., usually consisting of a platinum wire or dropping mercury, used to measure the dioxygen concentration in a solution.

- positive e. SYN: anode.

- quinhydrone e. one of several oxidation-reduction electrodes in which the ratio of the two forms (quinone-quinhydrone), determined by the hydrogen ion concentration, sets up a potential that can be measured and converted to a pH value (fails above pH 8).

- redox e. SYN: oxidation-reduction e..

- reference e. an e. expected to have a constant potential, such as a calomel e., and used with another e. to complete an electrical circuit through a solution; e.g., when a reference e. is used with a glass e. for pH measurement, changes in voltage between the two electrodes can be attributed to the effects of pH on the glass e. alone.

- resectoscope e. a wire loop e. that allows removal of tissue as well as cautery of the raw surface; used in endometrial ablation.

- rollerball e. a ball e. that rolls like a paint roller over surface tissue, cauterizing it; used in endometrial ablation.

- Severinghaus e. SYN: carbon dioxide e..

- silent e. SYN: indifferent e..

- therapeutic e. SYN: active e..

* * *

elec·trode i-'lek-.trōd n a conductor used to establish electrical contact with a nonmetallic part of a circuit

* * *

elec·trode (e-lekґtrōd) [electro- + hodos way] 1. a medium used between an electric conductor and the object to which the current is to be applied. 2. in electrotherapy or electrosurgery, an instrument with a point or surface from which to transmit an electric current to the body of a patient or to another instrument. 3. in electrodiagnosis, a needle or metal plate used to stimulate or record the electrical activity of tissue; see also lead².