Understanding the concept of concentration-dependent red-shift in synchronous fluorescence spectra: Prediction of λSFSmax and optimization of Δλ for synchronous fluorescence scan

The phenomenon of concentration-dependent red-shift of fluorescence, observed in multifluorophoric systems at high concentrations, has been successfully used in the analytical fluorimetry of systems like petroleum derivatives, humic substances, biological fluids, etc. From a detailed investigation of the phenomenon, it is inferred that the primary cause contributing to this phenomenon is the inner-filter effect especially under right angle sample geometry condition. In this work, a method based on inner-filter effect has been proposed to obtain an optimal Δλ which give the most intense synchronous fluorescence spectral maximum for solutions containing fluorophores at higher concentrations. The applicability of the method has been evaluated for some single fluorophoric samples (coumarin-152, quinine sulphate, rhodamine-6G and fluorescein) at high concentrations. The proposed formula and methodology were applied to certain multifluorophoric systems like diesel, transformer oil and humic acid.