Unique Oxygen Analyzer Combining a Dual Emission Probe and a Low-Cost Solid-State Ratiometric Fluorometer

A new oxygen analyzer combining a polymer-encapsulated dual-emission probe and a diode-based ratiometric fluorometer is described. The ratiometric fluorometer was configured to measure the relative fluorescence and phosphorescence intensity of the short-lived singlet and long-lived oxygen-quenchable triplet of [(dppe)Pt{S2C2(CH2CH2–N–2-pyridinium)}](BPh4), where dppe is 1,2-bis(diphenylphosphino)ethane. This luminescent dye was immobilized at 0.3% by weight in cellulose acetate/75% triethylcitrate and cast into a 0.5 mm-thick film. The dye molecule was excited with a blue light-emitting diode (LED) and the singlet and triplet emissions monitored by individual photodiodes at 570 and 680 nm, respectively. Oxygen can be accurately measured without interference from nonanalyte-induced intensity changes by monitoring the relative output of the two photodiodes. The output of the device was linear with oxygen concentration. The PO2(1/2) from the ratio-adapted Stern–Volmer plot was 9.6% oxygen (≈73 torr), offering a dynamic range of 0–90% O2. The device is stable and the oxygen measurements reproducible. Intentional photobleaching of ≈20% of the sensor dye had little effect upon the reproducibility of the oxygen measurements.