Electrode sensing

The principle of pH electrode sensing mechanisms which are based on glass or polymer membranes is well investigated and understood. Common to all potentiometric ion selective sensors, a pH sensitive membrane is the key component for a sensing mechanism. When the pH sensitive membrane separates the internal standard solution with a constant pH from the test solution, the potential difference E across the membrane is determined by the Nemst equation ... 

The effect of too high a scan rate is due to the existence of the interfacial capacitance, whereas the effect of uncompensated ohmic resistance is the result of the solution resistance between the working electrode surface and the point in solution at which the reference electrode senses this potential. These effects are explained in more detail below. 

Ion-selective electrodes sensing various ions, such as F , I, , CN , NH 4,... 

Electrochemical Behavior of Different Compounds at CNTs-based Electrodes. Sensing Properties... 

K. L. Cheng has proposed a theory of glass electrodes based on capacitor theory in which the electrode senses the hydroxide ion in alkaline solution (where an is very small), rather than sensing protons. [K. L. Cheng, Capacitor Theory... 

Does the glass electrode sense H OH in alkaline solutions ... 

The glass electrode senses other cations besides H. This becomes appreciable only when ah is very small, as in alkaline solution. We can t distinguish them from so the solution appears more acidic than it actually is. 

Direct Potentiometry Detemdnatiou of Hydrogen Chlonde Gas. A system has been described for the continuous monitoring of the HCl levels in gases or aerosols using a chloride-ion-selective electrode [IS]. This arose from a study on the loss of volatile decomposition products from poly(vinyl chloride) (PVQ and other chlorocarbon polymers in simulated fires. The method works well because of the excellent solubility of HQ in water, and the fact that the chloride electrode senses only free Q ion. Thus, other volatile chloride compounds will not be sensed. 

IDT electrode Sensing material 14.3 Schematic diagram of SAW device. 

An LC circuit was also coupled with a varactor for in vivo biopotential monitoring. Electrodes sense the variation in biopotential, which was used to alter the bias voltage of the varactor, thus causing its capacitance to change. The alteration in capacitance caused a variation in the LC resonant frequency, which was reflected in the impedance of the detection coil (Rustama 2007). 

The air-gap electrode [ 1 SO] may be used in the secondary quantitative stage just as conveniently as other designs of gas electrode and with the added advantage that the ion-selective electrode sensing surface does not make contact with the fouling proteins present in many clinical samples. The rapid determination of urea in blood over the range 10" —10" mol dm" has been reported for this electrode [150] and values were within 2.2 per cent of AutoAnalyzer values [379]. The excellent stability of the air-gap electrode facilitated the assay of 460 samples over 4 weeks, the cost per assay being just 2 per cent of that of the AutoAnalyzer method, but the response time per sample rose from an initial 3 min to about 5—6 min over the period [379]. 

Metal oxides Electronic conductors (SnO, TiOj, In O, etc.) mixed conductors (Ga Oj, WO, SrHOj, perovskites) ionic conductors (ZrOj, CeOj, etc.) metal oxides with metallic-type conductivity (RuO, COjO, PbOx, etc.) Gases (CO, CH, NOx, O, Cl, etc. vapor, alcohol dissolved oxygen O, Cl in solutions dissolved oxygen in molten metals, etc. (electrodes, sensing materials, membranes)... 

The reasons for chemical effects at the electrode sensing layer interface are related to the catalytic nature of the electrode material. The materials used are... 

Another effect is the increased production ( Catalysis ) of reaction partners by the metal electrode material. This can happen by, for example, breaking of hydrocarbons in more active radicals. Hence the reaction partners can diffuse to the three phase boundary (electrode/sensing layer/gas phase) and consequently this region becomes more active in gas detection. 

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