KINETICS AND IDENTIFIABILITY OF AN INTERMOLECULAR 2-STATE EXCITED-STATE PROCESS IN THE PRESENCE OF A FLUORESCENT IMPURITY

This paper presents a study analyzing the conditions for the recovery of the rate constants and the spectral parameters from the fluorescence decay surface due to three-state excited-state processes. The studied system models a Situation when, in addition to a fluorescence indicator which undergoes an excited-state reaction with a co-reactant, a fluorescent impurity is present. It is demonstrated theoretically that, if the fluorescence decay surface contains traces measured in the absence of co-reactant and additionally at two nonzero coreactant concentrations, all five rate constants can always be recovered. In some cases the measurement in the absence of co-reactant is not necessary. If the fluorescence decay surface is collected at three different emission wavelengths and two co-reactant concentrations, the ratios of the absorbances of the free and bound form of the fluorescent indicator can be determined. If two different emission wavelengths are used in combination with three excitation wavelengths (or three co-reactant concentrations), the ratios of the emission weighting factors of the free and bound form of the fluorescent indicator can be obtained. Under both previous conditions no spectral information about the fluorescent impurity can be acquired. The ground-state dissociation constant can be determined from the fluorescence decay traces excited at an isosbestic point.