Linear calibration function of luminescence quenching-based optical sensor for trace oxygen analysis

A mathematical response function derived from the Stern-Volmer equation was successfully applied to calibrate an optical oxygen (O₂) sensor using tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ditetrakis(4-chlorophenyl)borate adsorbed on silica gel as the O₂-sensitive material. The calibration of this optical sensor can be simply done by plotting the reciprocal of the luminescence intensity against the O₂ concentration (1/I vs. [O₂]). A single air sample injection method combined with an exponential dilution technique produces O₂ standards at various concentrations. The modified Stern-Volmer plots demonstrate excellent agreement with the well known Stern-Volmer plot (I₀/I vs vs. [O₂]). The proposed method has the advantages of simple O₂ standard preparation and no I₀ data being needed for calibration. The response and recovery times of the optical O₂ sensor are less than 0.2 and 1 s, respectively. The limit of detection is 2.6-3.6 ppm v/v. The photostability of the O₂-sensitive material is good and there is no sign of photodegradation after 12 h of continuous use.