Humic substances fluorescence

One laser photophysical study (6) has already been reported by Fischer et al. in which a variety of natural water samples and solutions of humic substance standards were excited at 355 nm (near the absorption maximum for excitation of humic substance fluorescence). Extensions of their work appear in this symposium. They resolved two components of transient absorption common to all the samples studied a component with maximum absorbance at 475 nm with a lifetime of several microseconds and a signal at 700 nm which was attributed to a solvated electron on the basis of is its sensitivity to N2O and on its absorption spectrum. 

In the case of exciplexes, where the aromatic chromophores are dissimilar, we might expect an increased red shift in the ground state absorption due to a greater charge transfer character to the transitions. It seems plausible then, that excimers and exciplexes account for the 350 nm excitation maximum for humic substance fluorescence, since they match the character of the fluorescence emission and may account for the observed excitation wavelengths. 

Schlautman, M.A., Morgan, JJ. (1993b) Binding of a fluorescent hydrophobic organic probe by dissolved humic substances and organically-coated aluminum oxide surfaces. Environ. Sci. Technol. 27, 2523-2532. 

Mayer, L.M., Schick, L.L., Loder, T.C. 1999. Dissolved protein fluorescence in two main estuaries. Marine Chemistry, 64, 171-179. Miano, T.M., Senesi N., 1992. Synchronous excitation fluorescence spectroscopy applied to soil humic substances chemistry. Sci Total Environ, 117/118, 41-51. 

Lead, J. R., Wilkinson, K. J., Starchev, K., Canonica, S. and Buffle, J. (2000). Diffusion coefficients of humic substances as determined by fluorescence correlation spectroscopy role of solution conditions, Environ. Sci. Technol., 34, 1365-1369. 

FLUORESCENCE Spectra. Fluorescence data are presented in Table V. All samples derived from drinking water gave an emission maximum between 417 and 430 nm, whereas the excitation maximum ranged between 346 and 365 nm. Miami IB showed an excitation maximum similar to the CFH samples, but the maximum was quite different from the one exhibited by the aquatic humic substances from the Satilla River. The emission maximum of these samples (Table V), however, was very similar. 

Mobed, J. J., S. L. Hemmingsen, J. L. Autry, and L. B. McGowan. 1996. Fluorescence characterization of IHSS humic substances total luminescence spectra with absorbance correction. Environmental Science Technology 30 3061—3065. 

Danielsen, K. M., Y. P. Chin, J. S. Buterbaugh, T. L. Gustafson, and S. J. Traina. 1995. The solubility enhancement and fluorescence quenching of pyrene by humic substances. Environmental Science and Technology 29 2162. 

Kenworthy, I. P., and Hayes, M. H. B. (1997). Investigations of some structural properties of humic substances by fluorescence quenching, In Humic Substances, Peats, and Sludges. Health and Environmental Aspects, Hayes, M. H. B., and Wilson, W. S., eds., The Royal Society of Chemistry, Cambridge, pp. 39 15. 

Fuentes, M., Gonzalez-Gaitano, G., and Garcfa-Mina, J. M. (2006). The usefulness of UV-visible and fluorescence spectroscopies to study the chemical nature of humic substances from soils and composts. Org. Geochem. 37,1949-1959. 

Figure 8.1. Fluorescence micrographs of Pinus sylvestris roots at 1mm (top) and 2 mm (bottom) behind the root tip after a treatment with HMS (high-molecular-size humic substances). Note the higher rate differentiation of the roots in respect to the control. Reprinted from Muscolo, A., Bovalo, F., Gionfriddo, F., and Nardi, S. (1999). Earthworm humic matter produces auxin-like effects on Daucus carota cell growth and nitrate metabolism. Soil Biol. Biochem. 31,1303-1311, with permission from Elsevier Limited.

Exner, A.,Theisen, M., Panne, U., and Niessner, R. (2000). Combination of asymmetric flow field-flow fractionation (AF4) and total-reflexion X-ray fluorescence analysis (TXRF) for determination of heavy metals associated with colloidal humic substances. Fresenius J. Anal. Chem. 366, 254-259. 

Structural and Interaction Studies of Humic Substances. Changes in structural aspects and interactions with other compounds usually affect fluorescence... 

Senesi, N., Miano, T. M., Provenzano, M. R., and Brunetti, G. (1991b). Characterization, differentiation, and classification of humic substances by fluorescence spectroscopy. Soil Sci. 152(4), 259-271. 

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