Equilibrium partition factor

The equilibrium partition factor is defined as the ratio of the concentration of species A inside and outside the pores. This concept was first introduced by Ferry in terms of a geometric exclusion effect [25]. Since the center of mass of the molecule, assumed to be a hard sphere, cannot be closer to the pore wall than the distance of the molecular radius, Ferry obtained... 

In summary, the bioavailability and observed toxicity of synthetic pyrethroids in sediment-water systems is influenced by a number of physicochemical factors, including the quantity and type of organic and inorganic matter in sediment and in water, as well as by temperature. The use of equilibrium partitioning calculations can be a useful tool for estimating the dissolved and potentially bioavailable fraction of pyrethroids. 

It is a great deal of work to actually determine a true equilibrium constant and most chemical separation methods speak in terms of values which are proportional to the actual equilibrium constant. At constant flow, the time that a given type of molecule is retained is related to the time for the void volume to pass after the sample is placed in a column or on a plate with the addition of the time for the net retention volume. If the flow remains constant, the temperature of the separation remains constant and no stationary phase is gained or lost, one can attempt qualitative identification using retention times. It is more reasonable to calculate the ratio of net retention volume to the void volume and call the result partition factor or capacity factor, k. ... 

This study is one of the earliest attempts to calculate equilibrium fractionation factors using measured vibrational spectra and simple reduced-mass calculations for diatomic molecules. For the sake of consistency I have converted reported single-molecule partition function ratios to units. 

Where I is the initial amount (g) of excipient in the solution, Wc is the weight of the container (g), Fs is the solution volume (L), and E, is the equilibrium partitioning constant, the ratio of the concentration of solute in the film to that in water, at equilibrium (66). This can be calculated from the more familiar, and referenced, solvent solvent partition coefficients. Plastics and rubber stoppers can also leach stabilizers and plasticizers into the contained injection volume. The extent of this can be calculated by considering the same factors described above. 

How is the equilibrium partition constant defined To which thermodynamic function(s) is the partition constant related, and which molecular factors determine its magnitude, in the case of... 

Inspection of Eq. 6-14 reveals that we do not need to learn anything new to understand air-water equilibrium partitioning of neutral organic compounds. All we have to do is to recall how chemical structures (controlling intermolecular interactions) and environmental factors (e.g., temperature, presence of salts or organic cosolvents in the aqueous phase) affect the vapor pressure and the aqueous activity coefficient of a given compound. Hence, our discussion of air-water partitioning can be quite brief. 

This last equation forms the basis for the EPA s sediment quality guidelines that are used to assess the potential toxicity of contaminated sediments. The idea is to simply measure Cs and foe, look up K0w in a table, compute the predicted Cw, and compare this result to established water quality criteria for the protection of aquatic life or human life (e.g., carcinogenicity risk factors). The use of this simple equilibrium partitioning expression for this purpose is currently the subject of much debate among scientists as well as policy makers. 

Bioavailability of organic chemicals is strongly dependent on aqueous solubility. The equilibrium partitioning theory has been applied to sediment toxicity studies, and it was concluded that uptake from sediment as well as from (pore) water is possible at the same time however, the exposure route in equilibrium is not necessarily important. For substances with log /< W < 5, the equilibrium partitioning theory is considered acceptable to assess the risk. For substances with log Kov/ > 5, a safety factor of 10 is applied, in order to include the additional uptake by sediment ingestion (Loonen et al. 1997). 

During mastication, nonvolatile flavor molecules must move from within the food, through the saliva to the taste receptors on the tongue, and the inside of the mouth, whereas volatile flavor molecules must move from the food, through the saliva and into the gas phase, where they are carried to the aroma receptors in the nasal cavity. The two major factors that determine the rate at which these processes occur are the equilibrium partition coefficient (because this determines the initial flavor concentration gradients at the various boundaries) and the mass transfer coefficient (because this determines the speed at which the molecules move from one location to another). A variety of mathematical models have been developed to describe the release of flavor molecules from oil-in-water emulsions. 

The IPAH model incorporated a number of factors that can modify the toxicity of the sediment-borne PAHs. Equilibrium partitioning was used to estimate the concentration of each PAH in the pore water of the sediment. The assumption was that the pore water material is the fraction that is bioavail-able. QSAR was also used to estimate the interstitial water concentration based on the octanol-water partition coefficient of several PAHs. Amphipods were used as the test organism to represent environmental toxicity. A toxic unit (TU) approach was used and the toxicity is assumed to be additive. The assumption of additivity is justified since each of the PAHs has a similar mode of action. Finally, a concentration-response model was formulated using existing toxicity data to estimate the probability of toxicity. 

Since almost all adsorptive separation processes are based on equilibrium partitioning, the most important factor to consider initially is the adsorption isotherm (equilibrium... 

For sediment-dwelling organisms, one important factor that determines the degree of exposure to xenobiotics in the sediment phase is the partitioning from the true sediment phase into interstitial water from which the xeno-biotic may then be accumulated by biota. Exposure of sediment biota to xenobiotics is, however, a complex process, since uptake may proceed either via particulate material or via interstitial water, or by both routes. In the equilibrium partition model the concentration of a xenobiotic in the interstitial water (Ciw) is given by the following relation ... 

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