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The fulvic acid (FA) sample isolated from the surface water of Lake Biwa has been authorized as a standard sample by the Japanese Humic Substances Society. The present paper aimed to provide information on their chemical characteristics, based on the diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, ramp cross polarization/magic angle spinning (CPMAS) 13C nuclear magnetic resonance (NMR) spectroscopy with phase-adjusted spinning side bands (PASS) method, excitation-emission matrix (EEM) fluorescence spectroscopy in combination with statistical analysis using the parallel factor model (PARAFAC), and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The DRIFT and 13C CP/PASS NMR spectra indicated high aliphaticity of the Lake Biwa FA. Its alkyl C accounted for 46% of total C with significant contribution of branched alkyl chains and aliphatic acids. On the contrary, the content of aromatic components such as phenolic compounds were smaller than soil FAs, which was also lined with a weaker fluorescence intensity compared to soil FAs. In EEM-PARAFAC, fluorescent component assignable to photorefractory or photo-degraded materials and that to microbially derived materials were relatively larger than those associated with soil FAs. In FTICR-MS using electrospray ionization (ESI) and negative mode detection, 2090 and 1369 peaks were detected and assigned to molecular formulas, respectively. Those were characterized by the large number of peaks including P and by the absence of molecular formulas similar to condensed aromatics and tannin. Although most of the molecular formulas had H/C and O/C ratios similar to lignin (67%) and aliphatics (26%), the number of molecular formulas similar to lignin was considered to be small because of the inclusion of N, P, or S in many of them and depending on the recent new criteria between lignin-like and aliphatic formulas.
Research papers (academic journals)
