Equilibrium partitioning experiments

Equilibrium Partitioning Experiments. The equilibrium partitioning of americium-III between gray hornblende schist and rock equilibrated water was determined in batch partitioning experiments with rectangular blocks of gray hornblende schist ( 5). The surface area sorption coefficient, K, was determined to be 4.5 . 5 mL/cm where... 

The most Important experimental fact to support this conclusion was given by the static (equilibrium) partitioning experiments (ref. 11 14), which confirmed the agreement of partition (distribution) coefficients, K q s, determined from both static and chromatographic measurements. Fig. 1 shows an example of such results. 

We again can use the results of the equilibrium partition experiments as a first approximation of the relative extraction rates to anticipate the trends we might see. Since the for selenate was an order of magnitude larger than the for selenite, we might anticipate that if there was any competition between the two species, the effect would be more significant with the extraction of selenite than with the extraction of selenate. 

In any equilibrium partitioning experiment using a micro-porous adsorbent and an external solution, one varies C°, and Ws for a given adsorbent. From equation (4.1.65), a plot of C° vs. Ws for a given adsorbent will be linear, the slope being equal to the quantity in brackets on the right-hand side of equation (4.1.65). Unless Vp > r it is clear that Kim = cy Cii will be less than 1, and the determination of the pore surface adsorption equilibrium relation (between and Ca) will be influenced by k, . This was demonstrated clearly in the adsorption of aromatic compounds (for example, napthalene) on microporous silica gel adsorbents by Alishusky and Fournier (1990). 

Ma, W.-C., A. Van Kleunen, J. Immerzeel, and P.G.-J. De Maagd. 1998. Bioaccumulation of polycyclic aromatic hydrocarbons by earthworms assessment of equilibrium partitioning theory in situ studies and water experiments. Environ. Toxicol. Chem. 17 1730-1737. 

The complexing ability of crown ethers in solvents of low polarity has been studied using two-phase partition experiments (Frensdorf, 1971b). The equilibrium between an aqueous solution of the salt (MX) and an organic solution containing the crown ether (Cr) is given by (2). Further dissociation of... 

Now, because the water-borne radioactive element is predominantly associated with the colloids, we no longer have a need for the distribution coefficient. There will still be a partitioning because the major portion of the radioactive elements will still be adsorbed to the sediment. This is a separate equilibrium partitioning coefficient, requiring a new experiment on the clay sediments and the colloids present. The partitioning colloid-clay ratio would most likely be dependent on the surface areas of each present in the sediments. A separate size distribution analysis has resulted in a sediment-colloid surface area ratio of 99 1 for the sediment. This results in a colloid retardation coefficient oiRc = 100 rather than Ri = 4.2 x 10 or i 2 = 6 x 10. ... 

In this model the unimolecular constants are relative to the turnover number and the bimolecular constants are chosen to yield equilibrium constants in units of millimolar. The model is primarily based on dead-end inhibition by CrATP, the Michaelis constant for ATP in the ATPase reaction, the isotope partitioning experiments of Rose et al. (65), and various binding and kinetic constants found in the literature. The final model was based on a computer simulation study attempting to discover what combination of rate constants would lit the isotope partition data and the observed kinetic and binding constants. 

Partition experiments were conducted under the same conditions as their reaction counterparts. To estimate the support volume (V - V,) a calibration curve of volume vs support mass was established (matrix volume [cm3] = 1.72 x support mass [g] - 0.07 R2 = 0.999). The equilibrium concentrations were attained 2 h after the immobilized lipase was added to the organic medium. 

So far two models have been employed to rationalize the solvation process the classical solution model, either the mole-fraction scale or any other concentration scale, and the Flory-Huggins model. The question is where to use which theoretical model to interpret the results of partitioning experiments, in which solute molecules distribute between two phases, a and ft. If the two phases are at equilibrium at the same temperature and the same pressure, /z = /xf. After rearrangement and applying Eq. (11-8), we can write... 

For liposome partition experiments freshly prepared liposomes of defined size are incubated with an aqueous solution of the analyte. The partition coefficient is calculated from the ratio of compound present in aqueous environment and lipid environment in equilibrium. 

Partitioning in the Presence of Surfactant. Partitioning experiments in the presence of Tween 80 were carried out in a manner identical to that discussed above except that 0.1% (w/v) of the surfactant was thoroughly mixed with the water phase before partitioning. Octanol/water partitioning studies carried out with only 0.1% Tween 80 (and no TFMS compound) present initially indicated that at equilibrium, the surfactant partitions approximately 60/40 in favor of the octanol phase. 

Although HSE concentrations are low in the Earth s mantle, they are not as low as one would expect from equilibrium partitioning between core forming metal and residual mantle silicate, as emphasized by new data on metal/silicate partition coefficients for these elements (Borisov and Palme, 1997 Borisov et al., 1994). Murthy (1991) suggested that partition coefficients are dependent on temperature and pressure in such a way that at the high P-T conditions where core formation may have occurred, the observed mantle concentrations of HSEs would be obtained by metal/silicate equilibration. This hypothesis has been rejected on various grounds (O Neill, 1992), and high P-T experiments have not provided support for the drastic decrease of metal/silicate partition coefficients of HSE required by the Murthy model (Holzheid et al., 1998). 

Conceptually, the solvent extraction process involves contacting the contaminated sludge with a solvent so that some of the PCB sorbed on the sludge will be desorbed. At long contacting times an equilibrium partitioning of the PCB between the sludge and the solvent phases (henceforth desorption equilibrium) will be obtained. Batch extraction experiments were performed to establish the equilibrium desorption charasteristics. 

These results have been confirmed in laboratory experiments on desorption (McGroddy et al. 1996), and underscore the limitations of equilibrium partition models for PAHs — although not apparently for PCBs. 

The method used for preparation of the PHEMA hydrogels was described in an earlier report (33). Fully hydrated samples equilibrated at room temperature were immersed in Millipore water at 37 0.5 °C for at least 2 weeks before calcification experiments commenced. The incorporation of citric acid into PHEMA was performed by the swelling equilibrium partition method using a 2.5 M citric acid solution. Prior to incubation in SBF or subcutaneous implantation of the hydrogels in rats, the citric acid-equilibrated gels were kept in Millipore water at 37 0.5 °C for one week. The hydrogels were sterilized by autoclaving for 20 min before implantation in the rats. 

Sediment/water equilibrium partitioning. This approach is related to a relative broad toxicological basis of water quality data. The distribution coefficient Kp, which is determined from laboratory experiments, is defined as the quotient of equilibrium concentration of a certain compound in sediment (Csx, e.g. in mg/kg) and in the aqueous phase (Cwx e.g. in mg/1). In practice, three categories of compounds can be distinguished ... 

Erythromycin extraction. Lye and Stuckey [81] reported the equilibrium partitioning of a microbial secondary metabolite, erythromycin, using both CLAs [formulated from 1% (w/v) Softanol 120 (alcohol ethoxylate type, Honeywill Stein) in decanol and 0.5% (w/v) SDS in water] and surfactant-containing, two-phase systems. The equilibrium partitioning of erythromycin was found to be strongly influenced by the extraction pH, and exhibited a marked change on either side of the of the molecule. A modified form of the Henderson-Hasselbach equation [16] could be used as a simple design equation to predict the equilibrium partition coefficient, as a function of pH. For extraction experi-... 

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