Transform method in three-dimensional fluorescence spectra for direct reflection of internal molecular properties in rapid water contaminant analysis

Abstract

Existing general analysis methods using fluorescence spectra in wavelength units make it difficult to determine the internal molecular properties of contaminants owing to the neglect of the actual physical meanings of spectral data. In this study, the relationships between spectral data and internal molecular properties were studied, and a corresponding transform method was proposed. A series of transforms were conducted on three-dimensional fluorescence spectra for increased relevance to energy level transition; the horizontal and vertical coordinates represented the Stokes shift and absorptive energy in transition, respectively. Through theoretical analysis and experiments with eight common organic chemicals, it was found that more complex molecular structures caused larger Stokes shifts and the more conjugation led to lower absorptive energy. For convenience in water contaminant analysis, five parameters of volume integrals were presented in various spectral regions corresponding to individual categories of substances. The effectiveness and universality of this procedure for rapid water contaminant analysis was assessed through long-term monitoring of river water samples. The proposed method can provide additional information on contaminant types and molecular properties on the basis of transformed spectral data, which can improve the richness, authenticity, efficiency, and convenience of early water quality analysis.