| quinhydrone electrode | One of several oxidation-reduction electrode's 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). (05 Mar 2000) |
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| ion selective electrode | An electrode half cell, with a semi permeable membrane that is permeable only to a single ion. The electrical potential measured between this and a reference half cell (e.g. A calomel electrode) is thus the Nernst potential for the ion. Given that the solution filling the ion selective electrode is known, the activity (rather than concentration) of the ion in the unknown solution can be measured. Commercial ion selective electrodes frequently use a hydrophobic membrane containing an ionophore, such as valinomycin (for potassium) or monensin (for sodium). A pH electrode is made with a thin membrane of pH sensitive (i.e. Proton permeable) glass. (18 Nov 1997) |
| oxidation-reduction electrode | An electrode capable of measuring oxidation-reduction potential. See: quinhydrone electrode. Synonym: redox electrode. (05 Mar 2000) |
| oxygen electrode | A sensitive method to detect oxygen consumption, involves a PTFE (Teflon) membrane. (18 Nov 1997) |
| therapeutic electrode | A small electrode whose exciting effect is used to stimulate or record potentials from a localised area. Synonym: exciting electrode, localizing electrode, therapeutic electrode. (05 Mar 2000) |
| electrode | <chemistry> Any terminal that conducts an electric current into or away from various conducting substances in a circuit (such as the anode or cathode of a battery). (09 Jan 1998) |
| electrode catheter ablation | A method of ablating the site of origin of arrhythmias whereby high energy electric shocks are delivered by intravascular catheters. (05 Mar 2000) |
| electrode knife | A blade-shaped electrical instrument used to cut tissues by means of a high-frequency electrical current. (05 Mar 2000) |
| enzyme electrode | A type of biosensor. An enzyme is immobilised on the surface of an electrode, and when the enzyme catalyses its reaction, electrons are transferred from the reactant to the electrode, and a current is generated, which can then be measured. (14 Nov 1997) |
| exciting electrode | A small electrode whose exciting effect is used to stimulate or record potentials from a localised area. Synonym: exciting electrode, localizing electrode, therapeutic electrode. (05 Mar 2000) |
| exploring electrode | An electrode placed on or near an excitable tissue; in unipolar electrocardiography, the electrode is placed on the chest in the region of the heart and paired with an indifferent electrode. (05 Mar 2000) |
| localizing electrode | A small electrode whose exciting effect is used to stimulate or record potentials from a localised area. Synonym: exciting electrode, localizing electrode, therapeutic electrode. (05 Mar 2000) |
| acromioclavicular disk | The articular disk of fibrocartilage usually found between the acromial end of the clavicle and the medial border of the acromion. Synonym: discus articularis acromioclavicularis, acromioclavicular disk, Weitbrecht's cartilage. (05 Mar 2000) |
| Airy disk | <microscopy> The image of a bright point object as focused by a lens system. With monochromatic light, it consists of a central point of maximum intensity surrounded by alternate circles of light and darkness caused by the reinforcement and interference of diffracted rays. The light areas are called maxima and the dark areas minima. The distribution of light from the centre to the outer areas of the figure was investigated mathematically by Sir George Airy. The diffraction disk forms a basis for determining the resolving power of an ideal lens system. The diameter of the disk depends largely on the aperture of the lens. The diffraction of light causing the Airy disk is a factor limiting the resolution of a well corrected optical system. The bright disk of light (surrounded by alternating dark and bright diffraction rings)that is formed by a perfect diffraction-limited lens, focusing an image of an infinitely small source of light. For a minute absorbing spot, the diffraction pattern is a dark Airy disk surrounded by brighter and darker diffraction rings. Since the Airy disk is the smallest unit that makes up the image of a luminous or absorbing object (formed by a properly corrected microscope lens in focus), the radius of the disk determines the limit of resolution of the microscope. (05 Aug 1998) |
| articular disk | A plate or ring of fibrocartilage attached to the joint capsule and separating the articular surfaces of the bones for a varying distance, sometimes completely; it serves to adapt two articular surfaces that are not entirely congruent. Synonym: discus articularis, articular disk, fibrocartilago interarticularis, fibroplate, interarticular fibrocartilage, intra-articular cartilage. (05 Mar 2000) |