Non-humic substances

Biochemical compounds such as carbohydrates, proteins (amino acids), and lipids present in humic substance fractions (humic acid, fulvic acid, and humin) pose a problem in determining and characterizing humic substances in various environments, especially in freshly deposited lake sediments where relatively large amounts of those biochemicals are present. Common separation methods cannot separate true humic substances from non-humic substances. According to Riffaldi and Schnitzer (1972b), 6N HCl hydrolysis efficiently removes nonhumic substances from soil humic acid. However, the following questions remain unresolved ... 

Danneberg, O. H. (1981). Possibilities for separation of humic and non-humic substances. Bodenkultur 32, 93-104. 

From the chemical standpoint, the humus is a very heterogeneous mate-rial, from which two groups of substances may be separated as follows humic substances themselves and a second group which includes non-specific substances, also referred to as non-humic substances. 

Bone protein was extracted following the method described by Sealy (1986). Bone chips were demineralized in a weak HCl solution, then soaked in 0.1 M NaOH to remove base-soluble humic substances. Remaining material, which is mainly collagen, but includes non-collagenous proteins, was... 

MnP is the most commonly widespread of the class II peroxidases [72, 73], It catalyzes a PLC -dependent oxidation of Mn2+ to Mn3+. The catalytic cycle is initiated by binding of H2O2 or an organic peroxide to the native ferric enzyme and formation of an iron-peroxide complex the Mn3+ ions finally produced after subsequent electron transfers are stabilized via chelation with organic acids like oxalate, malonate, malate, tartrate or lactate [74], The chelates of Mn3+ with carboxylic acids cause one-electron oxidation of various substrates thus, chelates and carboxylic acids can react with each other to form alkyl radicals, which after several reactions result in the production of other radicals. These final radicals are the source of autocataly tic ally produced peroxides and are used by MnP in the absence of H2O2. The versatile oxidative capacity of MnP is apparently due to the chelated Mn3+ ions, which act as diffusible redox-mediator and attacking, non-specifically, phenolic compounds such as biopolymers, milled wood, humic substances and several xenobiotics [72, 75, 76]. 

Humic substances. Analogous to the reactions described above, humic substances (the polymeric pigments from soil (humus) and marine sediments) can be formed by both enzymatic and non-enzymatic browning. High concentrations of free calcium and phosphate ions and supersaturation with respect to hydroxyapatite can sustain in soil, because adsorption of humic acids to mineral surfaces inhibits crystal growth (Inskeep and Silvertooth, 1988). A similar adsorption to tooth mineral in a caries lesion can be anticipated for polycarboxylic polymers from either the Maillard reaction or enzymatic browning. 

In natural water, singlet oxygen originating from humic substances has been shown, for example, to oxidize thioether pesticide contaminants such as disulfoton (Zepp et al. 1981). Irradiation of dilute hydrogen peroxide in the presence of various non-sunlight-absorbing herbicides results in enhanced oxidation of these substances (Draper and Crosby 1981). 

Humic Substance Interference. The probable interferences within the sample matrix were thought to be high molecular weight, non-chromatographable materials called humic substances. This conclusion was reached on the basis of (1) the results of the Grob column-performance text mix, (2) the type of successful on-column chemical cleanup, and (3) a review of the literature regarding the nonchromatographable constituents of natural waters. 

Thomas, J. D., and P. Eaton. 1996. The accumulation of amino-acids and humic substances in media conditioned by axenic and non-axenic duckweed (Lemna minor L.) and their possible ecological significance. Hydrobiologia 333 121-128. 

Belyaeva, E. Yu., Perminova, I. V., Kudryavtsev, A. V., and Novikov, A. P. (2006). Compension of non-exclusion effects during gel-permeation fractionation of humic substances. In Humic Substances—Linking Structure to Lunctions, Vol. 45-1, Frimmel F. H., and Abbt-Braun G., eds., Book Series Division of Water Chemistry, Engler-Bunte Institute, University of Karlsruhe, Karlsruhe, pp. 217-220. 

Almost all classes of compounds non-selective Flame ionization detector Non-halogenated volatile compounds (EPA 8015) Phenols (EPA 8041) PAHs (EPA 8100) —All other chemical compounds present in the sample will interfere with the target analytes. —TPH analyses are affected by naturally occurring organic compounds in soils with high humic substance content. 

Typical values of pK[nt and pfor a humic acid are 2.67 and 4.46. The introduction of the electrostatic factor into the equilibrium constant is analogous to the coulombic term used in the definition of the intrinsic surface complexation constants. In addition another binding site (WAH) is recognised which is thought to behave as a weak acidic phenolic functional group. Although this site does not contribute to the titratable acidity and, therefore, no pK is needed for proton dissociation, it is involved in metal complexation reactions. The total number of the three monoprotic sites is estimated from titratable acidity and then paired to represent the humic substance as a discrete non-interacting mixture of three dipro-tic acids, which act as the metal complexation sites. The three sites are... 

Benedetti, M.F., Milne, C.J., Kinniburgh, D.G., van Riemsdijk, W.H. and Koopal, L.K. (1995) Metal ion binding to humic substances application of the non-ideal competitive adsorption model. Environ. Sci. Technol, 29, 446-457. 

This technique has been applied by Iskandami and Petrzyk [316] to the determination of nitrate and nitrite in water. Chemically bonded amine materials have been used to remove interference by humic substances prior to the ion chromatographic determination of nitrate and sulphate in non saline waters. 

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