Characterisation and application of an oxygen membrane polarographic detector in a flow system for studying oxygen-evolving reactions

Abstract

A study has been made on the characteristics of an oxygen membrane polarographic detector (O₂-MPD) in a flow system, i.e., a system in which an inert gas, such as N₂, is used to sweep out the O₂ from a reaction vessel to the detector. Over a wide range of carrier gas flow-rates (10–215 cm³ min^–1) the response of the detector appeared to be fast enough (t_95% <1 min), accurate enough (±5%) and sensitive enough (P_o2 < 100 p.p.m.) toward injections of O₂ into the reaction vessel for the present applications. However, claims have been made for response times of less than 1 s and accuracies of ±0.01% for the metallised-membrane electrode, which, unlike the Clark electrode, was designed specifically for use in the gas phase. The detector response was also found to be proportional, over at least three orders of magnitude, to the volume of O₂ injected. A brief study of two well documented O₂-evolving systems (one chemical and one photochemical) yielded results that were in good agreement with those reported in the literature. The difficulties that arise when the oxygen is dissolved in a liquid, and the need for time for it to be transferred from solution to the gas phase, were examined and discussed.