Aldrich Humic Acid (aldrich + humic_acid)

Distribution by Scientific Domains


Selected Abstracts


Development of negligible depletion hollow fiber,protected liquid-phase microextraction for sensing freely dissolved triazines

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2009
Xialin Hu
Abstract A new sampling method, termed negligible depletion hollow fiber,protected liquid-phase microextraction, was developed for sensing the freely dissolved concentration (Cfree) and evaluating the availability of atrazine (ATR), desethyl atrazine (DEA), and simazine (SIM) in water. The sampling device was prepared by impregnating 1-octanol to both the pores and the lumen of a piece of polypropylene microporous hollow fiber membrane. After equilibrium and negligible depletion extraction, the 1-octanol in the lumen of the hollow fiber (10 ,l) was collected for determination of triazines. Determination of Cfree and the distribution coefficient to 1-octanol (DOW) can be performed with this technique. A wide linear working range (1,200 ,g/L) and low detection limits (0.1,1 ,g/L) were obtained for triazines. Measured log DOW values of DEA (1.44 0.04), SIM (2.06 0.06), and ATR (2.33 0.05) agreed well with those reported in the literature. The measured DOW values were independent of the chemical concentration and sample pH (pH 3,10) and negligibly affected by the sample salinity (0,500 mM), suggesting that environmentally relevant pH and salinity have no significant effects on the availability of triazines. Although a slight (,31%) increase of Cfree was observed, one-way analysis of variance indicated the Cfree of triazines were not significantly affected by the presence of Aldrich humic acid, Acros humic acid, and bovine albumin V (dissolved organic carbon [DOC], 0,100 mg/L). From 3 to 36% of the spiked triazines, however, were found to associate with the dissolved organic matter (DOM) in surface-water samples (DOC, 32.0,61.9 mg/L), suggesting the origin of the DOM is a key parameter in determining its association with and, thus, the availability of triazines. [source]


Soil organic matter beyond molecular structure Part II: Amorphous nature and physical aging

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2006
Gabriele E. Schaumann
Abstract Glassy, rubbery, and crystalline phases are representatives of supramolecular structures which strongly differ in order, density, and other characteristics. In this contribution, the amorphous nature of soil organic matter (SOM) is reviewed with respect to the glassy/rubbery model, glass transition mechanisms, interactions of SOM with water, and physical aging. Glass-transition behavior and physical aging are inherent properties of amorphous solids, and numerous spectroscopic investigations give insights into different domain mobilities of humic substances (HS). The correlation between sorption nonlinearity and glassiness of polymers and HS supports a relation between sorption and amorphicity in Aldrich humic acid. Further evidence is still required for the transfer to soil HS and SOM. Sorption and differential scanning calorimetry (DSC) data suggest a correlation between aromaticity and glassiness in HS, and the available data do currently not allow to decide unambiguously between specific sorption and hole filling as explanation. This needs to be verified in future research. Although parts of the investigations have up to now only been conducted with humic substances, the collectivity of available data give strong support for the glassy/rubbery conception of SOM. They clearly indicate that amorphous characteristics cannot be excluded in SOM. This is further supported by the observation of different types of glass-transition behavior in samples of whole humous soil. In addition to classical glass transitions in water-free soil samples, water surprisingly acts in an antagonistic way as short-term plasticizer and long-term antiplasticizer in a second, nonclassical transition type. Latter is closely connected with physico-chemical interactions with water and suggests water bridges between structural elements of SOM (HBCL-model). The gradual increase of Tg* in SOM indicates physico-chemical aging processes, which are not restricted to polymers. They may be responsible for contaminant aging, changes in surface properties and increased soil compaction in agricultural soils. [source]


Photodegradation of Soil Organic Matter and its Effect on Gram-negative Bacterial Growth

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 5 2008
Gabriela N. Bosio
ABSTRACT To learn more about the role of the reactive oxygen species (ROS) in the production of bioavailable products of the dissolved organic matter, we investigate here the effect of the photolysis (,exc > 320 nm) of a soil extract (SE) on the growth of bacteria isolated from the same soil as used for obtaining the extract. Comparative experiments with Aldrich humic acid (AHA) as substrate were performed. The photodegradation of the SE was evaluated with different techniques,UV,visible absorption spectroscopy, fluorescence excitation emission matrices (EEM) and Fourier transform infrared spectroscopy (FTIR). Known ROS scavengers were employed to study the effect of photochemically produced ROS on the photodegradation of the substrates. To evaluate the effect of irradiation on the bioavailability of the SE and AHA, photolyzed and nonphotolyzed substrates were added to different culture media and the growth of Pseudomonas sp. isolated from the soil and a strain of Escherichia coli were studied. The different results obtained were assigned to the dissimilar metabolisms of both bacteria. [source]


Kinetics of the sulfate radical-mediated photo-oxidation of humic substances

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2008
Pedro M. David Gara
The kinetics of the aqueous phase reaction of sulfate radicals with commercial humic acids and with organic matter extracted from vermicompost (VC) was studied by flash-photolysis. The results can be interpreted by a mechanism that in a first step considers the reversible binding of the sulfate radicals by the humic substances. Both the bound and free sulfate radicals decay to oxidized products. From experiments performed with Aldrich humic acids in the temperature range from 283 to 303 K, the enthalpy change associated with the binding process was estimated to be ,(36 11) kJ mol,1. 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40: 19,24, 2008 [source]