Partition coefficients Kd values

Krupka K. M. and Seme R. J. (2000) Understanding Variation in Partition Coefficient, Kd, Values, Volume III Review of Geochemistry and available Kd values for Americium, Arsenic, Curium, Iodine, Neptunium, Radium, and Technetium. Pacific Northwest National Laboratory, Richland, WA. 

US Environmental Protection Agency (EPA) (1999b) Understanding variation in partition coefficient, Kd, values Volume II. Review of geochemistry and available Kd values for cadmium, cesium, chromium, lead, plutonium, radon, strontium, thorium, tritium (3H) and uranium. Prepared for the EPA by Pacific Northwest National Laboratory. 

Understanding Variation in Partition Coefficient, Kd. Values, US Environmental Protection Agency, and Office of Air and Radiation, EPA 402-R-99-004A, Washington, DC, August 1999,... 

The use of the partition coefficient (Kd) has been considered questionable by some workers (10). However, to validate such use of the partition coefficient (Kd) one must realize that its values must be based on thermodynamic equilbrium of the system which is unlikely to happen in the natural aquatic system due to frequent fluctuations in temperature, pressure, pH,Eh, etc. The true thermodynamics equilibrium is sensitive to the internal and external stresses and relates to a limited number of concentrations encountered in the reaction system. Theoretical considerations dictate that the partition coefficient (Kd) computations, based on true thermodynamic equilibrium, remain constant as long as the other variables such as temperature, pH, Eh, pressure, etc. remain unchanged. 

Effect of Partition Coefficient and Dissociation Constant In the base case, the fraction of petroleum acid converted to soap (A/HA) is only 0.246, and the soap molar fraction is 0.309 (see Table 12.4). These values are affected by the partition coefficient Kd between water and oil and the acid dissociation constant Ka. Now let us see how sensitive these two parameters are. The data in Table 12.5 show that Kd is insensitive, whereas Ka is very sensitive. As Ka is increased, more acid is converted to soap. Accordingly, the soap molar fraction in the total surfactant becomes higher. As Xsoap is increased from the base case, the type III salinity limits are closer to those for the soap, which are lower. Thus, the mixture surfactant system becomes type II. As Xsoap... 

Fig. 9.4. The new mixed model for metals in lakes. Load (or dose) parameters are related to the input of metals to the lake (direct load and load from the catchment), the metal amount in the lake water is distributed into dissolved and particulate phases by the partition coefficient (Kd). Sedimentation is net sedimentation per unit of time (the calculation unit is set to 1 year for Hg and 1 month for Cs). The sensitivity parameters influence biouptake of metals from water to phytoplankton (but they may also be used in other contexts, e.g., to influence the Kd-values, as illustrated by the dotted line, or the rate of sedimentation). The biological or ecosystem variables include pelagic and benthic uptake, bioaccumulation and retention time in the five compartments (lake water, active sediments, phytoplankton, prey and predator fish). The ejfect parameter is the concentration of the metal in predatory fish (used for human consumption). One panel gives the calculation of concentrations, another the driving parameters (model variables should, preferably, not be altered for different lakes, while environmental variables must be altered for each lake). The arrows between these two panels illustrate the phytoplankton biomass submodel...

A. Results for different partition coefficients, Kd. Default value is 0.1 C. Different bioaccumulation rates plankton to prey. Default value is 0.16 E. Different predator outflow rates. Default value is 1/4... 

The HPLC was realized with a Waters solvent delivery system. Separations of oligomers were obtained with a Nucleosil 5 pm C-18 reverse phase column from S.F.C.C. (France) (8). The eluent was distilled water filtered through a 0.45 lm Millipore membrane. The starch was dissolved in DMSO and the eluent was DMSO/MeOH (85/15 v/v) in 0.5 M ammonium acetate. The colxamn set was diol silica gel from Merck 2 x Si 1000 Diol, 1 x Si 500 Diol, 1 X Si 100 Diol thermostated at 60 C. The detector was either a differential refractometer from Waters (R 401) or an IOTA (Jobin Yvon). The second on line detector was a light scattering detector (Chromatix CMX 100) or a spectropolarimeter (Perkin Elmer model 241 working at 365 nm with a flow cell of path length 10 cm and a 30 ll volume). The value of [a]D are expressed from [Ct]355 data using a corrective factor. The partition coefficient Kd is expressed as ... 

When the solute exists in only one form in each phase, then the partition coefficient and the distribution ratio are identical. If, however, the solute exists in more than one form in either phase, then Kd and D usually have different values. For example, if the solute exists in two forms in the aqueous phase, A and B, only one of which, A, partitions itself between the two phases, then... 

This distinction between Kd and D is important. The partition coefficient is an equilibrium constant and has a fixed value for the solute s partitioning between the two phases. The value of the distribution ratio, however, changes with solution conditions if the relative amounts of forms A and B change. If we know the equilibrium reactions taking place within each phase and between the phases, we can derive an algebraic relationship between Kd and D. 

Matsui and Mochida24) have determined the thermodynamic stabilities (log 1 /Kd) for a- and P-cyclodextrin complexes with a variety of alcohols (Table 2) and analyzed the results in connection with the physicochemical properties of the guest molecules by the multivariate technique. The log 1/Kd values were plotted against log Pe, where Pe is the partition coefficient of alcohol in a diethyl ether-water system. The plots for the a- and P-cyclodextrin complexes with eight 1-alkanols gave approximately straight lines with slopes of around one. 

Mathai and Singh have estimated the permeability coefficient P, using the formula P = kD where k is the partition coefficient and D is the diffusivity. They have used both parallel and series models to calculate P. The experimental values are always greater than measured values. The poor agreement between the experimental and calculated values is attributed to the polar-polar interaction between the epoxy group and nitrile group. 

Essentially, extraction of an analyte from one phase into a second phase is dependent upon two main factors solubility and equilibrium. The principle by which solvent extraction is successful is that like dissolves like . To identify which solvent performs best in which system, a number of chemical properties must be considered to determine the efficiency and success of an extraction [77]. Separation of a solute from solid, liquid or gaseous sample by using a suitable solvent is reliant upon the relationship described by Nemst s distribution or partition law. The traditional distribution or partition coefficient is defined as Kn = Cs/C, where Cs is the concentration of the solute in the solid and Ci is the species concentration in the liquid. A small Kd value stands for a more powerful solvent which is more likely to accumulate the target analyte. The shape of the partition isotherm can be used to deduce the behaviour of the solute in the extracting solvent. In theory, partitioning of the analyte between polymer and solvent prevents complete extraction. However, as the quantity of extracting solvent is much larger than that of the polymeric material, and the partition coefficients usually favour the solvent, in practice at equilibrium very low levels in the polymer will result. 

Four neutral lipid models were explored at pH 7.4 (1) 2% wt/vol DOPC in dode-cane, (2) olive oil, (3) octanol, and (4) dodecane. Table 7.5 lists the effective permeabilities Pe, standard deviations (SDs), and membrane retentions of the 32 probe molecules (Table 7.4). The units of Pe and SD are 10 6 cm/s. Retentions are expressed as mole percentages. Figure 7.22a is a plot of log Pe versus log Kd (octanol-water apparent partition coefficients, pH 7.4) for filters loaded with 2% wt/vol DOPC in dodecane (model 1.0, hlled-circle symbols) and with phospholipid-free dodecane (model 4.0, open-circle symbols). The dashed line in the plot was calculated assuming a UWL permeability (see Section 7.7.6) Pu, 16 x 10-6 cm/s (a typical value in an unstirred 96-well microtiter plate assay), and Pe of 0.8 x 10-6 cm/s... 

Once estrogens and progestagens have reached the waterways, a series of processes, such as, photolysis, biodegradation, and sorption to bed-sediments, can contribute to their elimination from the environmental water. Given the relatively low polarity of these compounds, with octanol-water partition coefficients mostly between 103 and 105, sorption to bed-sediments appears to be a likely process. Kd values calculated for estriol, norethindrone, and progesterone in a Spanish river (479,128, and 204, respectively) as the ratio between the sediment concentration (ng kg-1) and the water concentration (ng L 1) indicate that, in fact, these compounds exhibit a general tendency to accumulate in sediments. 

The values of q are plotted as a function of the equilibrium concentration. For constituents at low or moderate concentrations, the relationship between q and C can be generated. If n = 1, the (q-C) relationship will be linear (Eq. 9), and the slope of the line (i.e.,ITd) defines the adsorption distribution of the pollutant. Kd is generally identified as the distribution or partition coefficient, and is used to describe pollutant partitioning between liquid and solids only if the reactions that cause the partitioning are fast and reversible, and if the isotherm is linear. For cases where the partitioning of the pollutants can be adequately described by the distribution coefficient (i. e.,fast and reversible adsorption, with linear isotherm), the retardation factor (R) of the subsurface environment can be used as follows ... 

These points are emphasized by Figure 4, which is a series of plots of Ma°/Mtot Mtot in the same semilogarithmic scale for the dimerization stoichiometry with varying Kd (partition coefficient for the dimer), Km held constant. Data points from Figures 2 and 4 are collected in Table I with respect to slopes and values at the inflection point. 

The slope of this line is the distribution coefficient (Kd), which is the ratio of the arsenic concentration on the adsorbent (Cads) to the concentration of the associated remaining arsenic in the aqueous solution (Csdn). With each linear adsorption isotherm, Kd has only one value. That is, a linear distribution indicates that the partitioning of arsenic between the adsorbent and the solution is constant over the given range of arsenic concentrations (Eby, 2004), 221. If both concentrations (Cads and Csoin) are in the same units (such as molal), Kd is unitless. However, if the adsorbed concentration is given in molal and the dissolved concentration is molar, then Kd has the units of liter/kilogram. 

Our results for HOC partitioning in the presence of sorbed surfactant and micelles demonstrate that large differences can exist in the HOC sorption capacity of surfactant aggregates in micellar versus sorbed forms. This can be seen quite readily by calculating Kss values as a function of surfactant dose from the experimental KD values. The distribution coefficient defines the HOC mass balance and can be expressed as ... 

Figure 5. HOC distribution (KD) and sorbed surfactant partition (tf ) coefficients. Kaolinite concentration was 100 g/L, Individual Kss values filled circles) were determined from the KD values using eq 2 and the micellar partition and kaolinite sorption (/fWJT) constants below. Isotherm Ku values open circles) are from Table 4 (linear values), (a) = 1635 M 1. KmitT = 0.002 L/g. (b) = 280 M 1. = 0.0003 L/g. (c) Kmic = 51507 M 1. Kmin -...

HOC distribution coefficients (KD) between the immobile and mobile compartments varied as a function of solution chemistry and surfactant dose, KD values increased with increasing surfactant dose at low surfactant concentrations, but decreased at higher doses. This trend indicates that competition for HOC partitioning occurs between sorbed- and micellar-phase surfactants. Overall, the results of this study demonstrate that retardation of HOCs by surfactants sorbed to the solid phase can be significant and must be considered for proper evaluation of treatment/remediation alternatives that use surfactants. 

The partitioning of HCHs and DDTs between the SPM and DP was qualitatively assessed using the distribution coefficient K d and this is illustrated in Fig. 15.9 for station 1 and 2 respectively. The K d values for the two stations vary with depth implying that either the water bodies are not well mixed or more likely that the distribution of SPM is hetereogenous. The profile at station 2 (Fig. 15.9) is similar among OCPs. An increase of the Kd or log Kd value from the SML to the subsurface water and a decline towards the bottom water is distinctive for the profile at station 2. This may indicate that the characteristics of the water body or the SPM in the SML and subsurface water are different. The SML may be enriched with small or voluminous floating particulates, whereas subsurface water will typically be dominated by denser, sinking particles. The profile at station 1 shows that more HCHs and DDTs in the SPM appear proportionally in the SML and subsurface layer than in the mid-depth layer relative to the DP. The different profiles in the lower... 

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