Fluorescence fingerprint of fulvic and humic acids from varied origins as viewed by single-scan and excitation/emission matrix techniques

Excitation/emission matrix (EEM), single-scan excitation and synchronous fluorescence spectra of a series of FA and HA from distinct environments are presented. The EEM plots show at least four spectral features whose corresponding Ex/Em pairs relate to the α', α, β and γ (or δ) fluorophores previously found in natural waters spectra. The α' and α peaks, which identify typical humic-like components, are present in all samples, independently of the organic matter (OM) source. In FA, their Ex/Em pairs are ~260 nm/460 nm and ~310 nm/440 nm, respectively. In HA their excitation and emission maxima are red-shifted, the corresponding Ex/Em pairs being located at ~265 nm/525 nm and ~360 nm/520 nm, respectively. The appearance of β and γ (or δ) peaks is dependent both on the OM origin and on HS aging. The former (Ex/Em ~ 320 nm/430 nm), that has been associated with the incidence of marine humic-like material, is present only in a few marine and estuarine HA. It emerges as a shoulder on the α peak and its detection is dependent on a balance between its magnitude and the magnitude and emission maxima location of the α peak. The γ (or δ) peak (Ex/Em ~ 275 nm/315 nm in FA, and ~275 nm/330 nm in HA), on the other hand, is better visualized in FA than in HA diagrams. It has typical protein-, mainly tryptophan-like, fluorescence properties and appears with varied significance in a few marine and estuarine samples being hardly detected in samples from exclusively terrestrial environments. It is also shown in this study that with selected λex, λem and Δλ values, regular emission, excitation and synchronous spectra can, together, provide a good picture of the OM sources and aging for extracted HS. \textcopyright 2004 Elsevier Ltd. All rights reserved

Elemental compositions, FT-IR spectral and thermal behavior of sedimentary fulvic and humic acids from aquatic and terrestrial environments

Studies on elemental analysis, Fourier transform infrared spectroscopy (FT-IR) and thermal decomposition (thermogravimetry, TG; and derivative thermogravimetry, DTG) of sedimentary fulvic (FA) and humic acids (HA) from marine, estuarine, lacustrine and terrestrial environments are presented. In general, H/C and N/C atomic ratios, as well as the infrared spectra, reflected the extent of the influence of algal and/or terrestrial organic matter sources on the samples, the aquatic (both, marine and freshwater) humic substances (HS) being richer in nitrogen and more saturated, than terrestrial materials. Comparison of properties of FA and HA from the same parent sediments showed that the latter are relatively richer in nitrogen and unsubstituted aliphatic chains and poorer in carboxylic groups. FT-IR spectra showed that the nitrogen present is mostly as forming part of amide groups. Concerning thermal degradation, two main steps were observed for all samples: the first, relative to the loss of moisture, being located between 40°C and 100°C and the second between 270°C and 440°C. FT-IR spectra of the samples which had been heated to 90°C, 400°C and 900°C showed that, upon heating, the carboxyl content decreases (especially for FA), the aliphaticity decreases and the aromaticity increases (especially for HA), indicating that the 270°C-470°C degradation step might be related to decarboxylation and unsaturation losses. In spite of this, both kinds of HS, were shown to be highly thermo-resistant materials retaining most of their typical original infrared spectral features, even after being heated to 400°C. \textcopyright 2004 by The Geochemical Society of Japan

Fluorescence and DOC contents of pore waters from coastal and deep-sea sediments in the Gulf of Biscay

cited By 28International audienceFluorescence of waters from the Gulf of Biscay was investigated. Pore waters fluoresced more intensely and exhibited red-shifted spectra relative to overlying seawaters. Also, a blue-shift was observed going from coastal to open sea sites. Results indicate that continental inputs of fluorescent material reach the sea bed at all sites studied. Organic matter (OM) modifications within sediments were also observed. In the uppermost layer (6 cm), fluorescence intensity and dissolved organic carbon (DOC) concentrations decrease, followed by a red-shift in emission spectra with increasing depth. This may reflect the increase in OM molar mass due to humification. The reverse of these trends in the deepest sub-oxic sediments might be related to the degradation of OM released from the solid phase, resulting in dissolved fluorescent material with a relative paucity of oxygen-containing functional groups. A very good correlation of DOC with fluorescence was observed in all cores. © 2001 Elsevier Science Ltd. All rights reserved

Structural description of humic substances from subtropical coastal environments using elemental analysis, FT-IR and 13C-solid state NMR data

Elemental composition and spectroscopic properties (FT-IR and CP/MAS 13C-NMR) of sedimentary humic substances (HS) from aquatic subtropical environments (a lake, an estuary and two marine sites) are investigated. Humic acids (HA) are relatively richer in nitrogen and in aliphatic chains than fulvic acids (FA) from the same sediments. Conversely, FA are richer in carboxylic groups and in ring polysaccharides than HA. Nitrogen is mostly present as amide groups and for lake and marine HS the FT-IR peaks around 1640 cm-1 and 1540 cm-1 identify polypeptides. Estuarine HS exhibit mixed continental-marine influences, these being highly influenced by site location. Overall, the data suggest that aquatic and mixed HS are more aliphatic than has been proposed in current models and also that amide linkages form an important part of their structural configuration