Single standard calibration for an optical oxygen sensor based on luminescence quenching of a ruthenium complex

An optical oxygen (O₂) sensor consisting tris(4,7-diphenyl-1,10- phenanthroline)ruthenium(II) ditetrakis(4-chlorophenyl)borate adsorbed on silica gel has been successfully fabricated and used to continuously monitor O₂ gas at low concentration. The luminescence material shows a very strong and stable pink emission when excited by blue light and it is efficiently quenched by O₂. The calibration of the optical sensor can be simply done by a single standard flow injection method. The results demonstrate excellent linear Stern-Volmer behaviour when O₂ concentration is at low levels (0.0- 0.05% v/v), but the Stern-Volmer plot has a slightly downward curvature at higher O₂ levels. The two-site quenching model correlates well with the calibrated O₂ concentration range (0.0-0.55%). The t₉₅ response times of the sensor are < 0.2 s on going from 0.0% to 0.55% O₂ and < 1 s on going from 0.55% to 0.0% O₂. The sensor has high photostability, a long lifetime and no hysteresis in the response.