Real-time optimal combination of multifrequency information in phase-resolved luminescence spectroscopy based on rectangular-wave signals

A method for optimally combining multifrequency information in phase-resolved luminescence spectroscopy using rectangular-wave signals is proposed to improve the accuracy in the determination of the analyte concentration. From the rectangular-wave signal, phase-shift- and modulation-factor-based apparent lifetimes are estimated at each harmonic independently, together with their corresponding standard errors. Both the lifetimes and their standard errors are estimated on-the-fly from the Fast Fourier Transform (FFT) of the excitation and emission signals and applying error propagation theory. Independent determinations of the analyte concentration and their standard errors are then optimally combined in order to obtain an improved determination of the analyte concentration. The combination, formulated in a statistical framework, is a weighted average of different determinations proportional to the inverse of the variance of each independent determination. The proposed method has been applied to an oxygen measuring system to evaluate its accuracy and demonstrate its applicability in real-time measuring instruments. (C) 2016 Elsevier B.V. All rights reserved.