The development of a new polarographic sensor for measuring simultaneously both N2O and O2, in either gas or blood, is described. The cathode is made of silver, and it is shown that silver deposition on normal platinum or gold cathode electrodes can result in an enhancement of a PO2 signal, when measured in the presence of nitrous oxide. Silver can be deposited on the cathode by means of Ag+ ions diffusing through the electrolyte from an Ag/AgCl reference electrode. The use of an Ag cathode enables both O2 and N2O signals to be measured.

The polarographic reduction of halothane on silver cathodes was studied. Silver catalyses the reduction of halothane: two electrons are exchanged in the reduction process. Experiments using a rotating disc electrode showed a linear relationship between observed current and halothane concentration. A Silastic membrane-covered polarographic electrode was constructed using a silver cathode which gave a good linear response to changes in halothane concentration over the range 0.5% v/v halothane in nitrogen. Oxygen interferes with the measurement of halothane, but can be removed from a gas sample before analysis.

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A technique was developed for the in vivo determination of PO2 and PN2O with a catheter electrode using double-pulse polarography. The method was evaluated in dog studies comparing readings from the electrode with those from a mass spectrometer employing an in vivo probe. The oxygen readings obtained from the catheter electrode were also compared with values obtained by conventional blood-gas analysis. Good agreement was observed between the electrode and the mass spectrometer for both PO2 and PN2O. Similar agreement was found between the electrode readings and blood-gas analysis for PO2. In the presence of halothane, the electrode over-read for both PO2 and PN2O; a remedy is suggested. The in vivo electrode provides an effective, less expensive, alternative to the mass spectrometer for the on-line measurement of PO2 and PN2O in vivo.