The Fluorescence Characterization of Organic Matter Extracted from Humic Acid isolated from South-Bohemian Peat

conference proceedings

English

In this work, excitation–emission matrix (EEM) spectrometry was used for the first time to extensively study various organic matter extracted from humic acid isolated from South-Bohemian peat. Humic acid was isolated from South-Bohemian peat (locality Třeboň, Czech Republic). Humic acid was extracted using a procedure recommended by the International Humic Substances Society (IHSS). The peat humic acid (SBPHA) was placed in a cellulose thimble and Soxhlet gradually extracted for 12–50 h using trichloromethane, ethyl acetate, acetonitrile, acetone, n-propanol and methanol as a solvent. The organic matter fractions isolated from the peat humic acids were collected and concentrated by a rotary evaporator. Fluorescence spectra were recorded in aqueous solutions of 10 mg/L organic matter extracts using a FluoroLog luminescence spectrophotometer (Horiba Scientific, New Jersey, U.S.). The pH-value of samples was adjusted to seven using standard phosphate buffer. Total luminescence spectra (TLS) were obtained in the form of an excitation/emission matrix (EEM) by scanning the emission over the wavelength range of 300–600 nm, with the excitation wavelength increasing in 5 nm steps from 240 to 550 nm. 1st and 2nd inner filter effects were corrected. The fluorescence intensity values of samples (in counts per second, CPS) were corrected using the method devised by Lakowicz. The maxima are mainly located at excitation wavelengths in the ultraviolet region (around 250–260 nm). In the visible region (at an excitation wavelength 430 nm) only one maximum was observed out of sample set (methanol extract). The fluorescence EEM spectra of organic matter fractions (without sample extracted using CHCl3) were characterized by unique fluorophore centered at an excitation/emission wavelength pair (EEWP) of 250–260/415–505 nm (fluorophore type A-fulvic-like and/or symbol α’). A large bathochromic shift (red shift) of peak A was observed, depending on the polarity of the solvent. The fluorescence maximum observed in the humic-like region (300/430 nm) in extract of acetonitrile has not been seen in the other EEM spectra. The characteristic domain (fluorophore type C-humic-like and/or symbol α) for humic substances isolated from terrestrial origins with fluorescence maximum corresponding to excitation/emission wavelength pairs of 300–380/400–500 nm was observed in the acetonitrile extract. Further, the fluorescence EEM spectrum of fraction extracted with trichloromethane was characterized by one fluorescence peak located at EEWP of 270/305 nm (fluorophore type B-tyrosin-like and/or symbol γ). The maximum at 255/335 nm for extract of trichlormethane represent isolated fluorophore in the ultraviolet region; therefore, we denote the maximum of this fluorescent domain as peak A/T and/or α’/δ. Fluorophore A/T, was found only in chloroform extract. The maximum position is probably related to single aromatic systems and O-containing substituents. The shorter emission wavelengths measured in the EEM spectra can be associated with simple aromatic structures (one- to three-ring), and low molecular weight components. In contrast, the longer emission wavelengths can indicate the presence of condensed aromatic rings, and electron-withdrawing groups such as carbonyl-containing substituents, and hydroxyl and/or alkoxyl groups.

South-Bohemian Peat, humic acid, organic matter, fluorescence, EEM spectra, fluorophores

ENEV, V.; DOSKOČIL, L.; SEDLÁČEK, P.; KLUČÁKOVÁ, M.

23. 10. 2018

Université de Toulon and Aix-Marseille Université

Toulon

1

2

2