Optical sensors for oxygen: a log-gaussian multisite-quenching model

Optical sensors of oxygen that work on the principle of luminescence quenching by oxygen often generate non-linear, negatively deviating Stern-Volmer quenching plots. The cause for this deviation is usually ascribed to the presence of a multitude of quenching sites in the system. Most Stern-Volmer plots associated with optical oxygen sensors can, using three parameters, be fitted to a modified Stern-Volmer quenching equation in which it is assumed that there are two quenching sites. However, it is generally recognised that the curved oxygen optical sensor Stern-Volmer quenching plots are unlikely to be due to just two quenching sites, but rather an array of quenching sites, possibly Gaussian, due to a Gaussian distribution in lumophore natural lifetime. From the results in this paper it appears that a log-Gaussian distribution in Stern-Volmer quenching constant may be simpler and more appropriate than a simple Gaussian distribution model. The log-Gaussian distribution model has only two variables and was used to fit a wide variety of different Stern-Volmer quenching plots taken from the literature for a variety of different optical oxygen sensors. The significance of the log-Gaussian model and suggestions for its possible further testing are discussed. (C) 1998 Elsevier Science S.A. All rights reserved.