Carbon dioxide electrodes

Glutamate decarboxylase 4.1.1.15 L-Glutamate 4-Aminobutyrate/C02 Carbon dioxide electrode... 

Immobilized enzyme (wide range) membranes with oxygen, ammonia, or carbon dioxide electrodes Universal Sensors, USA... 

Gas-selective electrodes are a particularly important application of the glass electrode. For example, the carbon dioxide electrode is a self-contained system with a glass electrode and a concentric silver-silver chloride electrode enclosed by a C02 permeable membrane. The latter holds a thin film of bicarbonate solution in contact with the glass membrane, which provides a junction to the silver/silver chloride reference electrode. The electrode, which is illustrated schematically by Figure 2.2, has found extensive application in monitoring C02 levels in blood and probably will find increasing application in other systems that require continuous measurement of C02 partial pressures. The electrode response is based on the reaction... 

The first gas-sensing electrode based on a similar principle was the carbon dioxide electrode, developed to determine CO2 in blood. Later, sensors for other gases (e.g., SO2, NOx, and HCN, etc.) appeared on the market. 

Figure 5.11 A potentiometric carbon dioxide electrode. (Reproduced with permission from [10].)...

In this section the basic design and operation of these types of sensors are described. Examples of such sensors in common use are the Clark oxygen electrode [10] and the Severinghaus carbon dioxide electrode [11]. 

Electrolyte Thickness. A response time of the order of 10 to 20 seconds (T99) is desirable. This implies a solid polymer electrolyte thickness less than 25 jum. This is more or less the same for both oxygen and carbon dioxide electrodes. 

For the carbon dioxide electrode this translates into a stability of the order of 0.3 to 0.4 mV per hour. 

Fig.l compares the in vivo performance of oxygen and carbon dioxide electrodes with a non-aqueous, solid polymer electrolyte with electrodes containing a conventional liquid electrolytes. These electrodes have been operating for several weeks with virtually unaltered sensitivity. 

Very frequently used in analytical laboratories, GSE have been introduced into clinical laboratories in the last few years for the direct determination of blood gases on very small samples[31] and for intravascular monitoring of oxygen, tension of blood[32,34]. Non-invasive transcutaneous oxygen or carbon dioxide electrodes may alternatively be placed on the surface of the heated skin of neonates or adults the electrode response is directly proportional to arterial oxygen and carbon dioxide tensions[34-38]. 

Two gas electrodes are widely used in biology the ojygen electrode and the carbon dioxide electrode. Whereas the oxygen electrode is used in many diverse branches of biology, the carbon dioxide electrode is chiefly used to measure carbon dioxide in the blood. Both of these electrodes are described briefly in the following pages. 

The constituents of a carbon dioxide electrode are (1) a conventional glass pH electrode with a calomel reference electrode, (U) a thin plastic or teflon membrane which is permeable to ceirbon dioxide and not to other ions, and (tU) a standard bicarbonate solution, usually 0.005 M NaHC0 between the membrane and the glass electrode. 

When the electrode is dipped into a sample containing dissolved carbon dioxide, the carbon dioxide is allowed to diffuse into the bicarbonate solution by the permeable membrane. The pH of the bicarbonate solution changes, and this change is read by the glass electrode. This pH change is reflected by the pH meter which is directly calibrated for pCO. The response time of a carbon dioxide electrode is higher because the standard bicarbonate solution has to come into equilibrium with the sample. The same temperature variation relationship discussed with respect to the oxygen electrode applies here too. 

A diagram of the conventional carbon dioxide electrode is provided in Figure 2.7. 

The oo gen electrode is being widefy used in many different biological ejqjeriments vdierever there is a need of measuring oj gen. The carbon dioxide electrode on the other hand is mednly used for clinical purposes, often for measuring the carbon dioxide dissolved in blood or plasma. 

---