Search results for "Fractionation"
showing 10 items of 332 documents
Stable Cu isotope fractionation in soils during oxic weathering and podzolization
2011
Abstract Copper stable isotope ratios are fractionated during various biogeochemical processes and may trace the fate of Cu during long-term pedogenetic processes. We assessed the effects of oxic weathering (formation of Cambisols) and podzolization on Cu isotope ratios (δ65Cu). Two Cambisols (oxic weathered soils without strong vertical translocations of soil constituents) and two Podzols (soils showing vertical translocation of organic matter, Fe and Al) were analyzed for Cu concentrations, partitioning of Cu in seven fractions of a sequential extraction and δ65Cu values in bulk soil. Cu concentrations in the studied soils were low (1.4–27.6 μg g−1) and Cu was mainly associated with stron…
Characterization of aquatic humic substances and their metal complexes by immobilized metal-chelate affinity chromatography on iron(III)-loaded ion e…
2001
The analytical fractionation of aquatic humic substances (HS) by means of immobilized metal-chelate affinity chromatography (IMAC) on metal-loaded chelating ion exchangers is described. The cellulose HYPHAN, loaded with different trivalent ions, and the chelate exchanger Chelex 100, loaded to 90% of its capacity with Fe(III), were used. The cellulose HYPHAN, loaded with 2% Fe(III), resulted in HS distribution coefficients Kd of up to 10(3.7) mL/g at pH 4.0 continuously decreasing down to 10(1.5) at pH 12, which were appropriate for HS fractionation by a pH-depending chromatographic procedure. Similar distribution coefficients Kd were obtained for HS sorption onto Fe(III)-loaded Chelex 100. …
Continuous fractionation and solution properties of PIB. I. Search for the best mixed solvent and first results of the continuous polymer fractionati…
1987
To adopt a recently developed method for large scale fractionation (CPF = continuous polymer fractionation, a special kind of counter current extraction) to polyisobutylene (PIB), a systematic search for the best mixed solvent was performed. For this purpose, the essential parts of the phase diagrams solvent/nonsolvent/PIB were determined for 21 mixed solvents by cloud-point measurements; with eight systems of special interest, the molecular weight distributions of the polymers contained in the coexisting phases were also studied. On the basis of these experiments and of considerations concerning additional criteria for the performance of the continuous counter current extraction, the mixed…
Theory-based improvements of continuous polymer fractionation demonstrated for poly(carbonate)
1992
For the first time, a quantitative theoretical analysis (liquid/liquid phase equilibria treated by means of the continuous thermodynamics) of the operating characteristics of continuous polymer fractionation (CPF) was performed. The results of these calculations were compared with data published for CPF of polyethylene. It turned out that the efficiency of the conventional CPF corresponds to approximately two theoretical plates only. For this reason, several improvements, suggested by theoretical considerations, were realized experimentally, for which purpose the system dichloromethane/diethylene glycol/bisphenol-A polycarbonate was chosen. The pulsating sieve-bottom column was replaced by …
CPF : Continuous polymer fractionation
1992
A method is presented by means of which it is possible to fractionate polymers according to their solubility on a technical scale. The CPF consists of a continuous counter-current extraction process in which a homogeneous mixture of a molecularly or/and chemically non-uniform high molecular weight product is divided into two portions of considerably lower non-uniformity. The principle of the CPF is described in general terms and examples are given for the fractionation of homopolymers.
Continuous fractionation and solution properties of PIB. II. CPF optimization
1987
The quality of polymer fractionation depends on the choice of the mixed solvent as well as on the particular conditions of operating the continuous countercurrent extraction. With a polyisobutylene (PIB) sample of medium molecular weight Mw = 98,400 g/mol and U = (Mw/Mn) − 1 = 1.4 plus the mixed solvents toluene/2-butanone (TOL/MEK) and n-heptane/2-butanone (HEP/MEK) (both giving comparably good fractionation in equilibrium experiments), possible ways to optimize the CPF were tested. The mixed solvent HEP/MEK turns out to be superior to TOL/MEK for kinetic reasons. Due to the larger gap between its density and that of the pure polymer, the coexisting phases can still move through the column…
Pretreatment and fractionation of lignocellulosic barley straw by mechanocatalysis
2017
Abstract This study focuses on the mechanocatalytical process combining dilute acid pretreatment and mechanical processing driven by ball milling. Milled and hydrolyzed barley straw samples are subject to reducing sugar analysis by DNS assay and capillary electrophoresis. Optimization of the saccharification conditions was carried out with two different sulfuric acid concentrations, 0.5 mol kg −1 and 1.0 mol kg −1 , and compared. A significant yield of total reducing sugar (53.4%) was obtained from barley straw impregnated with sulfuric acid (1.0 mol kg −1 ) after milling for only 20 min. Glucose and xylose concentrations accounted for 3.5% and 11.3%, respectively. Strikingly, the present s…
Chemical characterization of peat fulvic acid fractions
1993
Abstract Milled peat fulvic acid (FA) preparation was fractionated by XAD-8 and conventional extraction methods. The fractions were further analyzed by IR and NMR and subjected to cupric oxide (CuO) oxidation. Carbohydrates of polydisperse FA were mostly not retained in the XAD-8 fractionation. The intensity of the signals due to double bonded carbons was much greater in the 13 C and proton NMR spectrum of the XAD-8 retained fraction than in the spectra of the XAD-8 non-retained or XAD-8 non-treated fractions. In CuO oxidation the main products of all FA fractions were 4-hydroxybenzaldehyde and 4-hydroxyacetophenone, both indicators of 4-hydroxyphenylpropane building blocks. Their concentra…
Isotopes Trace Biogeochemistry and Sources of Cu and Zn in an intertidal soil
2013
River floodplain soils are sinks and potential sources for toxic trace metals like Cu and Zn. We hypothesize that stable Cu and Zn isotope ratios reflect both the mobilization and the sources of metals. We determined the soil properties, the concentrations and partitioning of Cu and Zn, and variations in δ65Cu and δ66Zn values in a core obtained from an Aquic Udifluvent developed on a freshwater intertidal mudflat of the River Elbe, Germany. The core was sampled at 2 cm intervals to a depth of 34 cm, which corresponds to approximately 9 yr of sedimentation. Elevated concentrations of Cu (up to 320 μg g−1) and Zn (up to 2080 μg g−1) indicated anthropogenic pollution. At the time of sampling …
Xenograft rejection in marine sponges. Isolation and purification of an inhibitory aggregation factor from Geodia cydonium.
1981
In sponges there exists a graft rejection mechanism in which an inhibitory aggregation factor is involved. The inhibitory aggregation factor has been isolated from a culture medium containing dissociated cells of the sponge Geodia cydonium. Using ion-exchange and gel fractionation the factor was purified and shown to be electrophoretically pure. The factor has a molecular weight of 27000 and was characterized as a glycoprotein. The activity of the inhibitory aggregation factor was not affected by heat treatment, but treatment with trichloroacetic acid resulted in the irreversible loss of activity. The inhibitory aggregation factor affects the aggregation-factor-mediated reaggregation of dis…