OPTICAL SENSING OF OXYGEN USING PHOSPHORESCENCE QUENCHING

Optical measurements that exploit the ability of oxygen to quench the photoexcited states of other molecules provide an alternative to the s tandard electrochemical and paramagnetic methods of measuring molecula r oxygen concentration. In the present work we have re-examined the ph osphorescence quenching technique as a means of monitoring oxygen conc entrations in a gas stream at room temperature. Camphorquinone (CQ) is selected because it has strong absorption and emission bands in the v isible region, enabling the use of inexpensive silica fibre-optic ligh t guides. Determination of oxygen in the range 0.1-25% is easily achie vable and, for a 10 mu m thick PVC film containing CQ, the time to att ain 90% response is of the order of 10 s. Photooxidation and photoredu ction account for a significant loss of material under certain conditi ons of illumination and film composition. The use of triplet lifetime as a measure of oxygen concentration offers several advantages. In par ticular, by using an intrinsic property of the sensing molecule, varia tions in lamp intensity and photomultiplier sensitivity are avoided an d the effects of photobleaching reactions are minimized.