Polarographic oxygen-measuring cell

The polarographic oxygen-measuring cell, covered with membranes and working on the so-called Clark principle, consists of two electrodes arranged so as to be insulated, which are joined by a liquid or pastelike electrolyte. The electrode compartment is separated from the... 

The method is usually adopted when the transferring component is 02, since it is possible to monitor the dissolved oxygen concentration with a polarographic electrode(Clark cell). The method requires some precautions. The probe has an intrinsic time constant tp (the time needed to attain 63% of the reading after a stepwise concentration change) so that its output is not directly related to the actual concentration, especially when the concentration in the liquid phase changes rapidly. Indeed the measurement may be... 

On-site, dissolved oxygen is commonly measured using a membrane electrode of the polarographic type in a flow-through cell. The zero is commonly set using a saturated solution of sodium sulphite and the 100% saturated environment by holding the probe close to the surface of clean water. Below 1 ppm, electrodes provide only a qualitative measure of D02 due to slow electrode response (Wilkin et al., 2001). 

Radiometer pOz electrode, type E 5046 consists of a platinum cathode (20 /am diameter) and silver-silver chloride reference electrode placed in an electrochemical solution behind a 20 /am thick polypropylene membrane. A polarizing voltage of about 650 mV is applied. The polarographic current is about 10 " A per mm Hg of oxygen tension at 38°C. Zero current is lower than 10 A, response time less than 60 sec at 38°C 99% of full deflection. The PO2 electrode is used with the pH-Meter 27 GM or the Astrup Micro-Equipment, in conjunction with the Oxygen Monitor. The scale can be calibrated to the range 0-100 mm Hg p02. Thermostated cells provide measurements at constant temperature of volumes down to 70 /al. The small volume makes this cell useful to measure the PO2 of capillary blood. The cell is supplied with accessories for blood sampling. 

The electrochemical measurement of PO2 by use of a polarographic Clark cell offers the advantage of designing small and compact sensors which show a linear response to oxygen partial pressure. Figure 23-4 presents a sectional view of a combined transcutaneous sensor for tcp02 and tcpC02. 

Fig. 7. Reduction of dissolved oxygen concentration in a suspension of Hydro-genomonas H16 stirred under an atmosphere of 10 per cent oxygen, 10 per cent carbon dioxide, and varying concentrations of hydrogea 4.5 g cells dry weight per liter gas flow rate 300ml/min temperature 30°C 700rpm. Oxygen was measured using a polarographic electrode...

The accessibility of primary and metastatic squamous cell carcinomas (SCC) of the head and neck for tumor oxygenation assessment has meant that these tumors have received considerable attention with a large number of studies already documented (see Table 4.5). Reliable Oj-sensitive polarographic electrodes for measurement of O2 tensions in head and neck cancers were first used by Gatenby et al. (1985,1988). These authors convincingly demonstrated that hypoxia in advanced tumors was associated with a poor prognosis. 

Dilute 50 cm toluene with 50 cm of lithium chloride solution to serve as a blank. Pipette 5 cm of the sample solution and 5 cm of the blank solution into two polarographic cells and immerse these in the constant temperature tank of the cathode-ray polarograph (thermostatted at 25°C). Carry out the degassing operations with oxygen free nitrogen on the sample and on the blank solutions immediately before carrying out polarographic measurements. 

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