Phase fluorometric dissolved oxygen sensor

The design and performance of a ruggedised dissolved oxygen (DO) probe, whi ch is based on phase fluorometric detection of the quenched fluorescence of an oxygen-sensitive ruthenium complex, is reported. The complex is entrapp ed in a porous hydrophobic sol-gel matrix that has been optimised for this application. The LED excitation and photodiode detection are employed in a dipstick probe configuration, with the oxygen-sensitive film coated on a di sposable PMMA disc, which in turn is designed to guide Light into the film by total internal reflection. A key dement of the design is the common mode rejection of phase between the signal and reference channels, requiring ca reful selection of the relevant optoelectronic components. The advantages o f the phase fluorometric approach over intensity measurement are highlighte d. The phase detection electronics exhibits excellent long-term stability w ith a temperature coefficient of 0.00087. The sensor response exhibits exce llent signal-to-noise ratio (SNR) and reversibility and has been corrected for both temperature and pressure. The limit of detection (LOD) is typicall y 0.15 hPa or 6 ppb. The sensor has many potential applications but it has been designed primarily for application in waste-water monitoring. (C) 2001 Elsevier Science B.V. All rights reserved.