A new fluorescence index with a fluorescence excitation-emission matrix for dissolved organic matter (DOM) characterization

A series of fluorescence approaches have been employed to characterize the composition, transformation, and biogeochemical cycles of aquatic dissolved organic matter (DOM). However, there is no consensus on the protocols for elucidating DOM fluorescence spectra from protein-like (young DOM) to humic-like (old DOM) types, which are associated with the intrinsic fluorescence properties involved in the excitation/emission and detection of DOM. The central objective of this study was to evaluate the excitation-emissions matrices (EEMs)-average area of fluorescence intensity response using DOM fluorescence spectra collected on six different DOM surrogates using high-performance size-exclusion chromatography techniques. We evaluated criteria and protocols of a new Y fluorescence index (YFI) for comparison with McKnight fluorescence index (MFI), in which 280nm excitation coincides with independent inferences with response to emission wavelengths from 350 to 450nm. Our results demonstrate that YFI had sufficient distinguishing power to evaluate the characteristics of organic matter, including protein- and humic-type substances under various solution conditions. In addition, the YFI has good selectivity by showing its distinct signatures at better resolution of fluorescence intensity and little variation in different solutions including wastewater effluent-derived surface water. Although MFI has the advantage of fulvic acid-oriented correction, it revealed with a narrow spectral overlap range of 0.84-2.14 for DOM characterization of Suwannee River Humic Acid (SRHA), neomycin trisulphate salt hydrate (NTH), and bovine serum albumin (BSA). This narrow range of FI for DOM surrogate was improved with YFI, implying that all NOM substances fluoresce with considerable proportional ranges of 0.30-6.41. Our results suggest that the YFI values of the DOM surrogate data-set of fluorescence EEMs are likely proportionally lower FI of pahokee peat HA and leonardite HA relative to elliott soil HA, SRHA, and SRFA, while those of NTH, Streptomycin sesquisulfate hydrate, L-tyrosine, L-tryptophan, and BSA are higher FI.