Humic fractions maxima

Measurements of tan A as a function of temperature for the six humic fractions are plotted in Figures 2a-f. These measurements were made at pH 6.5. These plots show a maximum between 6 °C emd 25 °C. Equation 15 offers another method for the calcuation of the molar volume based on the emisotropy of the molecule and the temperature and viscosity at the experimental maximum of the tan A plots. The consequences of obtaining the volume in this manner are discussed by Mantulin and Weber U8J. 

Figures 3a-f show the emission and excitation spectra for all six humic fractions. The excitation and emission maxima are listed in Table III along with the maxima of the phase-resolved emission spectra. In each case the emission spectrum was scanned with the excitation maximum wavelength held constant, and the excitation spectrum was scanned with the emission maximum wavelength held constant. Several interesting features are noted. The two humic samples ( Figures 3a,b) each have two excitation maxima and it appears that a double peak has been merged into the emission scan as evidenced by the shoulder on the high energy side of the emission peak. Similarly it seems evident that the exaggerated shoulders in the emission spectra of all the fractions point to the inclusion of two emission peaks in each spectrum. This evidence suggests the presence of two chromophores in each humic fraction.

These considerations allow us to link the time required for humification (always directed to an increase in entropy) to the type of chemical transformations in humic system, which best suit this demand The system of NOM and HS should unavoidably evolve toward molecular compositions with the maximum number of isomers. Given that the overwhelming part of humic matter is being formed under oxic conditions, these structures are represented by low-molecular-weight aromatic and alicyclic acids. This suggests that under the same environmental constraints, the humification of NOM should lead to the formation of structures with an increased content of aromatic structures (or more precisely, the amount of DBE) and with a decrease in size similar to what was revealed by the results of data analysis on size-fractionated samples of humic materials shown in Figures 13.14A-D. 

Except for the humic acid fraction (130 mg g TOC), all maximum measured adsorption capacities are low ( 50 mg g TOC) in comparison with most other organics moreover the adsorption isotherms are very steep (Figs. 2—6). 

Fatty acids in humin from Lake Haruna sediments were analyzed for the fraction obtained by solvent (benzene/methanol 6 4) extraction followed by saponification 2N KOH aqueous solution at 200°C for 3 hours) extraction (Yamamoto and Ishiwatari, 1981). The fatty acids were composed of normal C12-C30 saturated monocarboxylic acids (maximum at Cig), unsaturated (Cie and Cis), and branched (C13, C15, and Cn) monocarboxylic acids. The fatty acid distribution in humin resembled that in humic acid. Total fatty acids accounted for 1.0% of the humin and probably originated from algae, bacteria, and higher plants. 

For humic acid many types of uptake curves were reported ranging from anion type adsorption edge (Fig. 4.5(B)) and uptake curves with a maximum (Fig. 4.6(C)) to almost pH independent uptake. These discrepancies might be partially due to difference in the chemical nature (molecular weight, functional groups) between particular samples referred to as humic acid. Humic acid is rather a mixture than single compound. Fractionation occurs by adsorption from such mixtures, i.e. the proportions of particular components in solution after equilibration with the adsorbent are different from those in the original solution. 

RP-HPLC and online 3DEEM detection were recently combined to study fluorescence properties of HS fractions as a function of polarity.SRFA and Aldrich humic acid (AHA) can be separated by stepwise RP-HPLC into several fractions, a red-shifted fluorescence maximum pattern and an increase in molecular size were found when the fraction changing from hydrophilic to hydrophobic. In a similar smdy, Lombardi and Jardrm separated a soil and marine fulvic acid into several classes of fractions with different fluorophores, which were related to their distinct origins. 

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