Assessment of inner filter effects in fluorescence spectroscopy using the dual-pathlength method - a study of the jet fuel JP-4

The integrity of most currently used fluorescence data analysis algorithms requires that a fluorophore present in a sample display the same spectral signature, apart from a single concentration-dependent scaling factor, regardless of its concentration or the concentrations of other components in the sample. Inner filter effects impede the utility of fluorescence spectroscopy by perturbing this spectral signature, rendering identification and quantification of fluorescent analytes difficult. The photophysical background theory of inner filtering is presented along with a comparison of existing correction schemes. The dual-pathlength method, a novel and simple experimental procedure for inner filter effect compensation, is introduced. The role of inner filtering in JP-4, a jet fuel contaminant detected by our laser-induced fluorescence/cone penetrometer instrument, is evaluated.