Humic acid samples

TabU II. Humic Acid Samples and Their Sources... 

No attempt was made to reduce the ash content of the humic acid samples, since drastic purification methods can cause abnormal changes in humate characteristics, and it was believed that most organic acids in their natural environment would be in salt form and associated with other colloidal matter. Though competition from displaced cations may have contributed to the smaller uptake by humic acid (HA II) in the adsorption stage (as shown in Table 2.1), any residual counterions should have had little effect on the metal-ion extraction step. 

The greater affinity of humic acids for copper or lead ions is clearly reflected in the extraction values reported in Fig. 2.1. In particular, far less of the adsorbed material was displaced by the salt solutions. The amount of lead retrieved by these extractants, and also with the mineral acids and buffer solutions, exceeded the copper recoveries, so copper appears to be more firmly bound than lead on the humic acid samples studied. 

In summary, examination of metal ion recoveries from humic acid samples by different chemical extractants has confirmed that in any extraction procedure very careful consideration must be given to the associated chemical equilibria and the impact of competing reactions. 

Figure 16.44. Correlation between the humification index determined by LIF spectroscopy (Huf) in whole soil samples and the humification index /t465 (Milori et al., 2002) determined by conventional fluorescence in the corresponding humic acid samples. The indexes are expressed as arbitrary units (a.u.) (Milori et al., 2006).

Landgraf, M. D., da Silva, S. C., and Rezende, M. O. O. (1998). Mechanism of metribuzin herbicide sorption by humic acid samples from peat and vermicompost. Anal. Chim. Acta. 368,155-164. 

Dialysis has been used to study the interaction between radionuclides and humic acid. The technique gives information on 1) the complexing capacity of the humic acid samples, i.e. the concentration of complexing sites, and 2) the radionuclide - humic acid complexes by a) its stoichiometry (i.e. metal ion/ligand ratio), and b) interaction constants. 

Recently, Weber and co-workers reported on the application of dialysis to the determination of the complexing capacity of fulvic acid for a series of metal cations (19, 20). In the present paper we report a further elaboration on the dialysis technique to allow simultaneous determination of complexing capacity for the humic acid sample, and interaction constants for the metal ion - humic acid complexes, as well as the stoichiometry of the latter. The technique furthermore opens up a possibility for an indirect determination of apparent ionization constants for the humic acids. 

It is important to note that [A]t cannot be regarded as a universal constant for a given humic acid sample, as it may be dependent of the nature of the participating metal ions, M (12). 

The present paper has demonstrated the versatility of the dialysis technique in studies of interactions between metal ions and humic acid samples. The method allows facile determination of interaction constants, as well as of complexing capacities of the humic acid samples. It is noteworthy that the method described here, without modifications, can be applied to other areas of complex chemistry involving macromolecular ligands. 

Tab. 2. Origin and some analytical characteristics of humic acid samples... 

Table IV. Pyrolysis-gas Chromatography Products From an Aquatic Humic Acid. Sample was taken from Volo Bog, Illinois. ...

NMR. Quantitative liquid-state carbon-13 nuclear magnetic resonance ( 3c NMR) spectra were recorded for humic and fulvic acid from Como Creek foam and for stream and foam fulvic- and humic- acid samples from the Suwannee River at the U.S. Geological Survey, laboratory in Arvada, CO. C NMR could not be performed on other humic substances due to insufficient sample or instrument availability. The acquisition parameters used were as follows C NMR spectra were recorded on a Varian XL-300 NMR spectrometer at 75 MHz. Each sample (200 mg of freeze-dried material) was dissolved in deuterated water and deuterated sodium hydroxide was added to ensure solution a total solution volume of approximately 6 to 7 mL. Spectra were recorded using a 30,000 Hz spectral window, a 45 pulse width, a 0.199 second acquisition time, and a pulse delay of 10 seconds for quantitative spectra. The number of transients was 10,000, and line broadening was 50 Hz. 

NMR Spectrometry. Liquid phase and NMR spectra were recorded on a Varian XL300 NMR spectrometer at carbon and nitrogen resonant fi equencies of 75.4 and 30.4 MHz, respectively, using a 10 mm broadband probe. Quantitative NMR spectra of the unreacted fulvic and humic acid samples were recorded in DMSO-d6, 99.9 atom % as previously described (23). INEPT (24) and ACOUSTIC (25) N NMR spectra were recorded on the aniline-reacted fulvic and humic acids. Refocussed INEPT (proton decoupled) spectra were recorded as previously described (9). ACOUSTIC spectra, with the exception of the bimessite catalyzed sample, were recorded with the use of paramagnetic relaxation reagent (100-200 mg chromium (III) acetylacetonate). Acquisition parameters included an 18,656.7 Hz spectral window (613.7 ppm), 0.5-s acquisition time, 45° pulse angle, 2.0-s pulse delay, and t delay of 0.1 ms. Neat formamide in a 5 mm NMR tube, assumed to be 112.4 ppm, was used as an external reference standard for all spectra. N NMR chemical shifts are reported in ppm downfield of ammonia, taken as 0.0 ppm. 

NMR Spectra of Soil Humic Acid Reacted with Aniline. ACOUSTIC NMR spectra of the soil humic acid reacted with the labelled aniline in the presence and absence of peroxidase and bimessite are shown in Figure 8. As discussed previously, the sharp peak at 315 ppm in the spectrum of the noncatalyzed reaction appears to represent the reaction product of aniline with a contaminant or pure component in the humic acid sample (9). Vertical expansion of the spectrum revealed a broad, low intensity imine peak underlying the sharp contaminant peak. This underlying imine peak is more clearly visible in the solid state spectrum of the sample (Figure 9B), where the sharp contaminant peak is broadened out presumably as a result of chemical shift anisotropy. Imine nitrogens were also... 

Humic Acid Sample Number Fulvic Acid Humin ... 

FIGURE 7. Densitometric traces of the isotachophoretic separation of a humic acid sample and two molecular weight fractions obtained from it (from Curvetto and Orioli, 1982). 

Bentonite was obtained from Fischer Scientific. Humic acid was obtained from Aldrich. An additional humic acid sample (BV) which was extracted from Chesapeake Bay sediments, was used in one set of adsorption experiments. The extraction and purification of this sample has been described in detail elsewhere (19). Further characterization of BV humic acid is also presented elsewhere (20). 

For most of the samples the molecular size distribution was not measured owing to the samples incomplete solubility, which shows their hydrophobic character. The molecular size distribution was determined ( 32) only for HALR humic acid sample (deposit of Ruppia maritima, Linnaeus) using size exclusion chromatography. The carbon content was measured by DOC and by a UV detector. Two peaks were... 

Cd was measured. The results are expressed as values. value is the ratio ofthe cadmium concentration in solid and liguld°phase given in cm g . As seen in Figure 9 the adsorption of Cd is rather strong on the humic acid. The values decrease as the solubility of the humic acid samples increase. ... 

Buurman, R, K. G. J. Nierop, J. Kaal, and N. Senesi. 2009. Analytical pyrolysis and thermally assisted hydrolysis and methylation of EUROSOIL humic acid samples—A key to their source. Geoderma 150, no. 1-2 10-22. 

The preparation of n-alkylammonium organocom-plexes is described elsewhere [16], The amounts of alkylammonium salts added to the humate solution were equivalent to the acidic groups (carboxyl and phenolic hydroxyl) of the humic acid sample. 

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