The use of solid-phase fluorescence spectroscopy in the characterisation of organic matter transformations

• We highlighted interests of solid-phase fluorescence (SPF) spectroscopy,
• We examine changes in the organic matter dynamic during composting process,
• We showed strong links between SPF spectroscopy, Rock-Eval pyrolysis and 13C NMR,
• Results confirm the pertinence of SPF spectroscopy to monitor OM dynamics.

Given its high sensitivity and non-destructive nature, fluorescence excitation–emission matrix (EEM) spectroscopy is widely used to differentiate changes and transformations of dissolved or water-extracted organic matter (OM) in natural environments. The same technique applied directly on solid samples (solid-phase fluorescence spectroscopy, SPF-EEM) provides accurate results when used with pharmaceutical products or food samples, but only a few studies have considered natural OM. This study reports on the use of SPF-EEM on solid compost samples and emphasises the way the different maturation phases can be distinguished with fluorophores closely resembling those found in dissolved samples. A very good correlation has been found with data from Rock-Eval pyrolysis, nuclear magnetic resonance (13C CPMAS NMR), and humic-fulvic acid ratios determined by conventional NaOH-extraction. SPF-EEM appears as a much simpler method than the conventional ones to detect transformations in natural OM samples with low mineral contents. However, direct application to soil samples requires some additional studies.

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