Electrodes Clark membrane

For application in enzyme electrodes COD has been mainly immobilized by surface fixation (Table 7). As early as 1977, Clark had patented the polarographic analysis of free and esterified cholesterol by means of free as well as immobilized COD and CEH with anodic H2O2 indication. Cholesterol in food and serum samples has been determined by using COD bound to a collagen membrane via glutaraldehyde and coupled to a Pt electrode (Clark, 1978). A similar probe has been devised by Bertrand et al. (1979). In this sensor the enzyme membrane was not protected by a semipermeable membrane. Interferences were compensated for by difference measurements between an enzyme sensor and an enzyme-free membrane electrode. The lower detection limit was 0.05... 

Mitochondria Substrate Clark electrode (standard membrane) Clark electrode (high-sensitivity membrane) Hb02 method... 

The Clark Type Sensor. The working and reference electrodes, e d, are part of the main body, c, which is screwed into the external body a. It is held tightly against the membrane g which is held in place by o-ring f. A thin layer of the electrolyte, b, is held between electrode and membrane. 

Oxygen concentration is determined electrochemically using a membrane oxygen electrode (Clark sensor). Oxygen is consumed by micro-organisms, and the reduction in oxygen consumption with time is a measure of biological activity. 

PO2 can be determined by a means of a PO2 electrode (Clark electrode). In this technique, oxygen diffuses from the blood sample across a gas-permeable membrane into an electrochemical system which consists of a platinum cathode and a silver/silver chloride anode. Reduction of the oxygen occurs at the cathode, resulting in the generation of a current which can be measured, the current being directly proportional to the PO2. This is an example of an amperometric technique... 

One important application of amperometry is in the construction of chemical sensors. One of the first amperometric sensors to be developed was for dissolved O2 in blood, which was developed in 1956 by L. C. Clark. The design of the amperometric sensor is shown in Figure 11.38 and is similar to potentiometric membrane electrodes. A gas-permeable membrane is stretched across the end of the sensor and is separated from the working and counter electrodes by a thin solution of KCl. The working electrode is a Pt disk cathode, and an Ag ring anode is the... 

FIGURE 6-18 Membrane-covered oxygen probe based on the Clark electrode. (Reproduced with permission from reference 60.)... 

Flow injection analysis (FIA) (Ruzicka and Hansen), since 1975 In continuous flow, stopped flow or with merging zones (FIA scanning or intermittent pumping) Adapted voltammetric electrodes Membranes for Partial dialysis Membrane amperometry (Clark) Differential techniques (Donnan) Computerization, including microprocessors Special measuring requirements in plant control (to avoid voltage leakage, etc., Section 5.5)... 

The history of glucose enzyme electrodes starts with the first device developed in 1962 by Clark and Lyons from the Children Hospital in Cincinnati [3], Their first device relied on a thin layer of GOx entrapped over an oxygen electrode (via a semipermeable dialysis membrane), and monitoring the oxygen consumed by the enzyme-catalyzed reaction ... 

The first enzyme biosensor was a glucose sensor reported by Clark in 1962 [194], This biosensor measured the product of glucose oxidation by GOD using an electrode which was a remarkable achievement even though the enzyme was not immobilized on the electrode. Updark and Hicks have developed an improved enzyme sensor using enzyme immobilization [194], The sensor combined the membrane-immobilized GOD with an oxygen electrode, and oxygen measurements were carried out before and after the enzyme reaction. Their report showed the importance of biomaterial immobilization to enhance the stability of a biosensor. 

The dissolved oxygen content of a solution can be determined by measuring the diffusion current that results at a selected voltage. The Clark electrode was developed for this purpose and various modifications have subsequently been introduced. It consists basically of a platinum electrode separated from the sample by a membrane which is permeable to oxygen, e.g. Teflon or polyethylene. A reference electrode of silver/silver chloride in potassium chloride is used to complete the system (Figure 4.21). When a voltage that is sufficient to give the... 

The problem with the Clark electrode is that some of these requirements have solutions that are opposing. For instance, flow dependence may be reduced by employing a thicker membrane but this would occur at the cost of increased response time. As a result, most commercially available systems are design compromises that sacrifice a part of some desirable feature. It should he noted that an optical measurement technique where oxygen and/or electrolyte is not consumed will be free of the drawbacks mentioned above. 

Amperometrically, using a Clark-type electrode. This is a platinnm electrode snr-rounded by a gas-permeable membrane. 

L. C. Clark first suggested in 1956 that the test solution be separated from an amperometric oxygen sensor by a hydrophobic porous membrane, permeable only for gases (for a review of the Clark electrode see [88]). The first potentiometric sensor of this type was the Severinghaus CO2 electrode [150], with a glass electrode placed in a dilute solution of sodium hydrogenocarbonate as the internal sensor (see fig. 4.10). As an equilibrium pressure of CO2, corresponding to the CO2 concentration in the test solution, is established in the... 

The potentialities offered by chemical processes catalyzed by enzymes immobilized in a polymeric matrix are obvious and are now successfully utilized in various ways [6, 13, 16, 17, 40, 43,44, 50, 58, 61], This idea was introduced into electroanalytical chemistry by Clark and Lyons [9], who proposed a glucose electrode, with glucose oxidase immobilized between cuprophane membranes and with amperometric determination of the hydrogen peroxide formed by the reaction... 

An elecrochemical device for detecting dissolved oxygen content. The well known Clark electrode consists of a platinum wire tip surrounded by a thin film of electrolyte solution that is shrouded by a plastic membrane. The membrane is permeable to oxygen, but impermeable to... 

Electrodes based on the principle of Clark s electrode with gas permeable membranes. These sensors are used in many different fields. 

Clark oxygen electrode. [D. t. Sawyer, A. Sobkowiak, and J. L. Roberts, Jr., Electrochemistry for Chemists, 2nd eel. (New York Wiley. 1995).] A modern, commercial oxygen electrode is a three-electrode design with a Au cathode, a Ag anode, a Ag I AgBr reference electrode, and a 50-(im-thick fluorinated ethylene-propylene polymer membrane. Leland Clark, who invented the Clark oxygen electrode, also invented the glucose monitor and the heart-lung machine. 

We begin by pointing out that this concept of covering an electrode surface with a chemically selective layer predates chemically modified electrodes. For example, an electrode of this type, the Clark electrode for determination of 02, has been available commercially for about 30 years. The chemically selective layer in this sensor is simply a Teflon-type membrane. Such membranes will only transport small, nonpolar molecules. Since 02 is such a molecule, it is transported to an internal electrolyte solution where it is electrochemically reduced. The resulting current is proportional to the concentration of 02 in the contacting solution phase. Other small nonpolar molecules present in the solution phase (e.g., N2) are not electroactive. Hence, this device is quite selective. 

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