Fulvic acids fluorescence spectra

Cory, R.M., Miller, M.R, McKnight, D.M., Guerard, J.J., and Miller, RL. (2010). Effect of instrument-specific response on the analysis of fulvic acid fluorescence spectra. 

Molecular fluorescence spectroscopy is a commonly employed analytical method that is sensitive to certain chemical properties of FA (9-13). Fulvic acid s molecular fluorescence is principally due to conjugated unsaturated segments and aromatic moieties present in the macromolecule (14). Several types of fluorescence spectra can be measured, including an excitation emission matrix or total luminescence spectrum, constant offset synchronous fluorescence, excitation spectra, and emission spectra, furnishing the researcher with useful data. The ability to resolve and select multiple fluorescent species makes these approaches extremely useful for studying FA relative to its chemical reactivity. 

Figure 9.6. Plot of McKnight et al. (2001) fluorescence index (FI) vs. % aromaticity for a variety of isolated fulvic acid samples. The % aromaticity was calculated using C-NMR as the ratio of the area of the aromatic carbon region to the total area of the spectrum. There is a strong correlation between FI and % aromaticity (linear regression equation is y = -O.Qllx + 2.1 (B - = 0.85), and the power function regression is y = 3.94 x where x=% aromaticity and y = FI). Note that while Deer Creek (DC) flows into Snake River (SR), the aromaticity drops due to the aromatic fulvic acids sorbing to iron oxide in the streambed, but there is httle change in the FI, indicating a robustness of the index.

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