Carbon dioxide monitoring in compost processes using fibre optic sensors based on a luminescent ruthenium(II) indicator

Novel fibre-optic CO2 sensors have been fabricated using the luminescent pH -sensitive tris[2-(2-pyrazinyl)-1,3-thiazole]ruthenium(II) indicator immobi lised onto poly(vinyl alcohol), cellulose, poly(hydroxyethylmethacrylate), or poly(tetrafluoroethylene)(PTFE) layers. The dyed support is soaked in ph osphate buffer and covered by a gas-permeable silicone membrane. The best t erminals, in terms of CO2 sensitivity (0-0.027 MPa partial pressure), limit of detection (1.0 x 10(-5) MPa), reproducibility of fabrication, temperatu re effect (20-50 degreesC tested) and long-term stability (4 months checked ) are achieved using PTFE, 0.1 M internal buffer concentration and pH 8.0. Under these conditions, the optical sensor displays negligible cross-talk t o molecular oxygen. The rugged CO2 sensor has been successfully applied to extended on-line monitoring of the analyte in the gas effluent of vegetable compost processes carried out in a home-made pilot digester.