Partition coefficients adsorption

Kommalapati RR,Valsaraj KT, Constant WD (2000) Soil-water partition coefficients, adsorption/desorption hysteresis, desorption kinetics and bioavailability of chlorinated organic compounds at the PPI site. Submitted to Hazardous Substance Research Center, Louisiana State University, Baton Rouge, LA... 

Gas chromatography is primarily an analytical separation technique. However, since the basic process is an equilibration of a solute between two immiscible phases, the chromatographic technique may be used to measure such physical properties as activity coefficients, second virial coefficients of gas mixtures, partition coefficients, adsorption and partition isotherms, and complex formation constants. Other properties which can be measured with less accuracy, from secondary measurements or from temperature variation studies, include surface areas, heats of adsorption, and excess enthalpies and excess entropies of solution. A number of reviews and discussions on these measurements have appeared in the literature. The present work is restricted to a review of activity-coefficient measurements. 

Pawliszyn, 1995). In SPME, a phase-coated fiber housed within a syringe is exposed to the sample medium (water or air), allowing the analytes to be adsorbed on the fiber coating. For organic compounds having high partition coefficients, adsorption equilibrium can be attained within minutes. After sample adsorption, the fiber is withdrawn into the needle, which is then inserted into the heated injection port of the GC. The adsorbed analytes are thermally desorbed and analysis proceeds in the same manner as in normal GC/MS analysis. 

For the PC model, adsorption can be seen as purely partitioning behavior. This model ascribes a thermodynamic partitioning coefficient ( adsorption separation factor ) to each solute to describe adsorption quantitatively. No explicit thermodynamic contribution of the surface site to the adsorption process nor competitive adsorption effects are considered. 

The partition coefficient and aqueous solubility are properties important for the study of the adsorption, distribution, metabolism, excretion, and toxicity (ADME-Tox) of drugs. The prediction of the ADME-Tox properties of drug candidates has recently attracted much interest because these properties account for the failure of about 60 % of all drug candidates in the clinical phases. The prediction of these properties in an early phase of the drug development process could therefore lead to significant savings in research and development costs. 

In the low concentration limit the adsorption isotherm is alinear law as was the partition coefficient,andjustastheisothermdeviatesfromlinearityoutsideofthelowconcentration limit,sotoodoesthepartitionrelationbetweenthetwoliquidphases. 

Barrett and Thomas (10)proposed that these effects of differential monomer adsorption could be modeled by correcting homogeneous solution copolymerization reactivity ratios with the monomer s partition coefficient between the particles and the diluent. The partition coefficient is measured by static equilibrium experiments. Barrett s suggested equations are ... 

In contrast to straight phase or adsorption chromatography, partition chromatography involves the separation of sample molecules owing to their different partition coefficients between the liquid stationary and mobile phases. The liquid stationary phase is located in the pores of a sorbent, ideally only acting as a support, making no contribution to the retention of the sample molecules. 

The distribution of Th is not controlled by decay processes that can be used to constrain its supply rate, but the Th- Ra pair can be used to provide some constraints on Th adsorption. In an area where Ra concentrations are constant, mobile Ra is supplied by only recoil and decay of mobile Th. The amount of Th that is absorbed on surfaces can be obtained if the amount of mobile Ra is constrained (i.e., the Ra partition coefficient and the groundwater concentration are known) and can be compared to an estimate of the recoil rate of Ra (using the measured Rn activity in the groundwater) from the host rock. In this way, Luo et al. (2000) calculated that recoil from the host rock was insufficient to explain the amount of mobile Ra, and argued that adsorbed Th provided much of the mobile Ra then Th partition coefficients can... 

In gas chromatography the value of the partition coefficient d ends only on the type of stationary phase and the column temperature. It is independent of column type and instrumental parameters. The proportionality factor in equation (l.ll) is called the phase ratio and is equal to the ratio of the volume of the gas (Vg) and liquid (V ) phases in the column. For gas-solid (adsorption) chromatography the phase ratio is given by the volume of the gas phase divided by the surface area of the stationary phase. 

Soils and vadose zone information, including soil characteristics (type, holding capacity, temperature, biological activity, and engineering properties), soil chemical characteristics (solubility, ion specification, adsorption, leachability, cation exchange capacity, mineral partition coefficient, and chemical and sorptive properties), and vadose zone characteristics (permeability, variability, porosity, moisture content, chemical characteristics, and extent of contamination)... 

The simplest type of isotherm is the linear-distribution coefficient, A d.12 It is also called the partition coefficient, 7. 58 The equation for calculating adsorption at different concentrations is... 

This equation is widely used to describe adsorption in soil and near-surface aquatic environments. Another widely used linear coefficient is the organic-carbon partition coefficient Koc, which is equal to the distribution coefficient divided by the percentage of organic carbon present in the system as proposed by Flamaker and Thompson.131... 

Winters and Lee134 describe a physically based model for adsorption kinetics for hydrophobic organic chemicals to and from suspended sediment and soil particles. The model requires determination of a single effective dififusivity parameter, which is predictable from compound solution diffusivity, the octanol-water partition coefficient, and the adsorbent organic content, density, and porosity. 

As shown in Figure 24.7, the average partition coefficients for ether- and alcohol-based oxygenates are much lower than for BTEX. Based on this, it would be expected that adsorption systems... 

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