Fulvic acids analysis

Applications of NMR, ESR, thermal analysis, spectrophotometry, gas chromatography, and GC-MS to humic and fulvic acid analysis have been reviewed by Schnitzer [452]. 

Soil extracts are usually very complex. In water samples, humic and fulvic acids make analysis difficult, especially when polar substances are to be determined. Multidimensional chromatography can also make a significant contribution here to this type of analysis. 

In multiresidue analysis, where more analytes with a wide polarity range need to be determined, large transfer volumes are required, and consequently, the selectivity is lower. However, since the major interferences in water analysis are the polar humic and fulvic acids, removing this early eluting interference in coupled-column RPLC will also be feasible in multiresidue methodology. 

Various destructive and non-destructive methods of analysis have been tested and H-l and C-13 NMR have, among other techniques provided valuable structural information on soluble humic acids and fulvic acids 48, Humin, on the other hand has withstood detailed non-destructive analysis. 

Dixon, A. M. and Larive, C. K. (1997). Modified pulsed-field gradient NMR experiments for improved selectivity in the measurement of diffusion coefficients in complex mixtures application to the analysis of the Suwannee River fulvic acid, Anal. Chem., 69, 2122-2128. 

Gamble, D. S., Underdown, A. W. and Langford, C. H. (1982). Copper(II) titration of fulvic acid ligand sites with theoretical, potentiometric and spectro-photometric analysis, Anal. Chem., 52, 1901-1908. 

Despite the advances made in high-performance liquid chromatography in recent years, there are still occasionally applications in which conventional column chromatography is employed. These methods lack the sensitivity, resolution and automation of HPLC. They include the determination of urea herbicides in soil, polyaromatic hydrocarbons, carbohydrates, chloroaliphatic compounds and humic and fulvic acids in non-saline sediments. The technique has also been applied in sludge analysis, e.g. aliphatic hydrocarbons and carboxylic acids. 

The humates present in soil are polyelectrolytes and bear some similarity to polyacrylic acid and polymethacrylic acid (49, 50). The molecular weight distribution for the humates is considerable fulvic acid fractions of 1,000 daltons have been isolated (51) while humic acid molecular weights obtained by gel chromatography are in the range 17,000 to 100,000 daltons according to the type of soil from which it was extracted (52). However, ultracentrifugation analysis indicates a molecular range of 2,000 to 1,500,000 daltons for humic acids (55). 

Data from the Na-pyrophosphate partial extractions and estimates of organic C contained in humic and fulvic acids from spectroscopic determinations show poor reproducibility over time. Analysis of data from re-sampling in September 2007 show significantly lower results over bedrock mineralisation than the original orientation survey conducted in April 2007, although the general pattern appears to be preserved. Re-analysis of the duplicate field samples in the same batch indicates that this variation largely reflects seasonal variations in metal content of the soils, possibly related to rainfall patterns, but also includes a component of laboratory variation between batches. 

Methods of Structural Analysis. The most significant differences between structural models 1 and 2 are the prominent aromatic carbon content in model 1 and the aliphatic alicyclic ring content in model 2. Determinations of aromatic carbon content and ring content of fulvic acid might be useful for identifying sources and processes of degradation and fractionation. However, neither of these procedures is simple and straightforward. 

Flodin C, Ekelund M, Boren H, Grimvall A (1997) Pyrolysis-GC/AED and Pyrolysis-GC/ MS Analysis of Chlorinated Structures in Aquatic Fulvic Acids and Chlorolignins. Chemo-sphere 34 2319... 

When environmental samples are analysed by reverse-phase liquid chromatography, the most widely used technique, polar interferences usually appear (ions, plus humic and fulvic acids). This makes it difficult to determine more polar compounds that elute in the first part of the chromatogram. This is specially important when detection is not selective, e.g. UV detection, which is one of the most common techniques in routine analysis. In such cases, multidimensional chromatography plays an important role. 

A problem for both humic- and yellow substances is that for these groups of experimentally defined components of different sources, each analysis will be ambiguous in terms of relative composition and molecular weight distribution. Additionally it appears that almost every scientist working in this field has developed his own extraction procedure (Weber and Wilson, 1975 Mantoura and Riley, 1975 a Schnitzer, 1976 Stuermer and Harvey, 1977). Different extraction times and -procedures result in different compositions of the organic constituents (Laane and Kramer, 1984). Soil humic-and fulvic acids, often used for studies on the interaction with trace elements, and those derived from water have certainly not the same composition and contain not the same distribution of functional groups. Therefore, results should be compared with care (Buffle, 1980 Buffle et al., 1984). 

The fluorescence properties of two fulvic acids, one derived from the soil and the other from river water, were studied. The maximum emission intensity occurred at 445-450 nm upon excitation at 350 nm, and the intensity varied with pH, reaching a maximum at pH 5.0 and decreasing rapidly as the pH dropped below 4. Neither oxygen nor electrolyte concentration affected the fluorescence of the fulvic acid derived from the soil. Complexes of fulvic acid with copper, lead, cobalt, nickel and manganese were examined and it was found that bound copper II ions quench fulvic acid fluorescence. Ion-selective electrode potentiometry was used to demonstrate the close relationship between fluorescence quenching and fulvic acid complexation of cupric ions. It is suggested that fluorescence and ion-selective electrode analysis may not be measuring the same complexation phenomenon in the cases of nickel and cobalt complexes with fulvic acid. 

In addition to the absorbance of visible and ultraviolet light, fulvic acids are major fluorophores in natural waters. Analysis of the fluorescence of... 

There are relatively few studies that have measured the P content of dissolved organic material however, available information appears to indicate that the P content of DOM can act as a broad indicator of the conditions under which the DOM was formed. The P content of dissolved fulvic acids and colloids in aquatic ecosystems has been determined by elemental analysis (McKnight et al., 1985 1997). The P content of fulvic acids varies by more than an order of magnitude across different ecosystems (Table II). Fulvic acids from Thoreau s Bog in Massachusetts have a high P content compared... 

Ultimately, the usefulness of tracer methods will partially depend upon how readily they can be incorporated into a field study. Methods that can be applied to filtered water samples are less labor intensive than those requiring some type of fractionation, such as the use of small-volume XAD-8 columns or ultrafiltration. However, column or ultrafiltration fractionation can be streamlined to make them practical for field studies, and the better resolution of DOM chemistry may make the extra effort worthwhile. If fulvic acid or high molecular weight fractions are isolated in a study, these can be saved for potential subsequent analysis of trace moieties as motivated by initial results. Finally, the overall question being addressed in a particular experimental or field study will determine which tracer methods, if any, are included. 

Thermal analysis of humic-mineral complexes has shown there is an overall reduction in the decomposition temperatures of humic acid that has been com-plexed to a mineral surface. Changes in the exothermic peak temperatures of humic substances in the free and complexed state are well-documented for synthetic mineral complexes with humic and fulvic acid (Schnitzer and Kodama, 1972 Tan, 1977 Schnitzer and Ghosh, 1982) as well as for authentic soil complexes. 

Schnitzer, M., and Kodama, H. (1972). Differential thermal analysis of metal-fulvic acid salts and complexes. Geoderma 7, 93-103. 

Figure 4.5. Fluorescence excitation-emission matrix spectra of humic acids (HAs) isolated from sewage sludge (B) and two soils either unamended (TH1 and TH2, respectively) or amended with 3901 ha-1 of sewage sludge (THB1 and THB2, respectively) sampled from the surface (s, 0-25cm) and subsurface (ss, 25-50cm) layers. Reprinted from Bertoncini, E. I., D Orazio, V., Senesi, N., and Mattiazzo, M. E. (2005). Fluorescence analysis of humic and fulvic acids from two Brazilian oxisols as affected by biosolid amendment. Anal. Bioanal. Chem. 381,1281-1288, with permission from Springer.

Figure 4.6. Fourier transform infrared spectra of humic acids (HAs) and fulvic acids (FAs) isolated from pig slurry (PS), unamended soil (PSO, and soils amended with 90 and 150m3ha 1yr 1 of PS for 7 years (PS90 and PS150, respectively). Reprinted from Hernandez, D., Plaza, C., Senesi, N., and Polo, A. (2006). Detection of copper(II) and zinc(II) binding to humic acids from pig slurry and amended soils by fluorescence spectroscopy. Environ. Pollut. 143, 212-220, with permission from Elsevier, and from Hernandez, D., Plaza, C., Senesi, N., and Polo, A. (2007). Fluorescence analysis of copper(II) and zinc(II) binding behavior of fulvic acids from pig slurry and amended soils. Eur. J. Soil Sci. 58, 900-908, with permission from Blackwell Publishing.

Bertoncini, E. I., D Orazio, V., Senesi, N., and Mattiazzo, M. E. (2005). Fluorescence analysis of humic and fulvic acids from two Brazilian oxisols as affected by biosolid amendment. Anal. Bioanal. Chem. 381,1281-1288. 

Hern ndez, D., Plaza, C., Senesi, N., and Polo, A. (2007). Fluorescence analysis of copper(II) and zinc(II) binding behavior of fulvic acids from pig slurry and amended soils. Eur. J. Soil Sci. 58, 900-908. 

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