Phase fluorometric dissolved oxygen sensor

Abstract

The design and performance of a ruggedised dissolved oxygen (DO) probe, which is based on phase fluorometric detection of the quenched fluorescence of an oxygen-sensitive ruthenium complex, is reported. The complex is entrapped 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 disposable PMMA disc, which in turn is designed to guide light into the film by total internal reflection. A key element of the design is the common mode rejection of phase between the signal and reference channels, requiring careful selection of the relevant optoelectronic components. The advantages of the phase fluorometric approach over intensity measurement are highlighted. The phase detection electronics exhibits excellent long-term stability with a temperature coefficient of 0.00087. The sensor response exhibits excellent signal-to-noise ratio (SNR) and reversibility and has been corrected for both temperature and pressure. The limit of detection (LOD) is typically 0.15 hPa or 6 ppb. The sensor has many potential applications but it has been designed primarily for application in waste-water monitoring.