Oxygen sensing electrodes

Cholesterol The end point for the cholesterol reaction can be determined by following dye formation. Additionally, the amount of oxygen consumed can be measured amperometricaHy by an oxygen-sensing electrode (see Electro analytical techniques). The H2O2 produced by cholesterol oxidase requires phenol to produce dye. 

In addition to the method described above, there are at present, on the market, several glucose analyzers offered by several commercial companies, wherein the individual injects approximately 20 microliters of serum. This is then incubated with glucose oxidase and the peroxide or oxygen generated is measured with an oxygen sensing electrode. These instruments cannot perform the test on 1 xl nor are they designed for that purpose at the present time. 

According to this equation, for an amperometric oxygen-sensing electrode covered by a membrane of 100 pm thickness the steady-state current will be attained 38 s after changing the oxygen concentration (D = 3.9 10 cm Vs). Half of the steady-state value is reached at... 

Oxygen saturation in solution could be established in both reactors using an oxygen sensing electrode. The substrate solution generally had the following initial composition 0.282 g phenol,p.a., 9.0 g NaCl, 0.2 g MgClo-6H 0, 0.15 g CaClp-2Hj,0,... 

Active immobilized-enzyme used for the production of an oxygen-sensing electrode for determining uric acid Active immobilized enzyme... 

Figure 1, A sketch of the oxygen sensing electrode. The ultrathin polymer film is applied to the exposed platinum end.

The idea of separating the gas sample by a gas-permeable membrane from the actual internal sensing element is common to several types of electrochemical and some optical sensors. The potentiometric Severinghaus electrode and the amperometric oxygen Clark electrode have already been discussed. Actually, most types of sensors can be used in this configuration and the conductometric sensor is not an exception (Bruckenstein and Symanski, 1986). 

The oxygen sensing properties of such electrode systems were measured at first. The reproducibility of the output current versus oxygen tension is shown in Figure 2. The coefficient of correlation was 0.987 using eighteen data points. 

Ammonia 368, 540 gas sensing electrodes 366 Ammonium 540-541 Amorphous silicon (a-Si) 99 Amperometric 907, 913 biosensors 359 detection 876, ell9 no sensor 930 oxygen electrodes 915 ultramicroelectrode 907 Amyloglucosidase 676 Analytical approximation 912 Anatoxin-a(s) 335 Aniline 985... 

Oxidoreductases 916 Oxido-reductive properties e66 Oxygen 105 free radicals 185 gas-sensing electrode 366 reduction 915... 

Andreescu et al. introduced a 96-electrode well-type device enabling oxygen sensing for monitoring respiratory activity of biological cells.65 65 The principal set-up of the multichannel dissolved oxygen sensor system (DOX-96) is schematically in shown in Fig. 14.13. This highly parallelized approach shows successful... 

Sensors may also use multiple electrolytes (referredto as electrolyte chains), and two examples of these are shown in Figure 13.Id and e. In both examples, a Na2SO4 auxiliary electrode is used with a sodium ion conductor so that the sensing electrode reaction is given by Equation (13.5). The difference between the two cases is that, in Figure 13.Id, the sodium ion conductor is used with another cation (strontium) conductor, whereas in Figure 13.le the sodium ion conductor is used with an anion (oxygen) conductor. In both cases, an equilibrium reaction is required to relate the... 

A major factor in the selection of a reference electrode is the reference potential established. If the reference potential is close to the potential at the sensing electrode, the cell voltage will be small and thus tend to be more stable than a large voltage. For example, the oxygen partial pressure established by a Pd + PdO reference electrode... 

Ramamoorthy, R., Akbar, S.A. and Dutta, P.K. (2006) Dependence of potentiometric oxygen sensing characteristics on the nature of electrodes. Sens. Actuators B, 113 (1), 162-8. 

Enzyme immunoelectrodes involve the spatial coupling of the sensor, the immunocomplex, and the catalytic amplification by indicator enzymes. Like the sensor systems described above, enzyme immunoelectrodes are based on common principles of EIA. The choice of enzymes for EIA is rather restricted and is further diminished when electrodes are to be used for detection. So far only GOD, catalase, and HRP have been combined with oxygen-sensing polarographic sensors. An overview of enzyme immunoelectrodes is given in Table 21. 

Figure 5 Oxygen-sensitive or -sensing electrode (coiudesy of Arthur H.

In potentiometric devices, an open-circuit voltage is measured. They also consist of an electrolyte (that is also typically made of YSZ) and two electrodes (also typically made of platinum). One of the electrodes is the working electrode (WE) - also called the sensing electrode (SE) - and the other is the reference electrode (RE). Both YSZ and Pt are suitable for high-temperature applications such as exhaust gas detection. They work as follows the electrolyte is an ionic conductor and there is a thermodynamic equilibrium between ambient oxygen, electrons in the electrodes and mobile oxygen ions. In the simplest case, the following reaction takes place in the electrodes ... 

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