Partition coefficient normalization

Under this umbrella, a number of different applications lie, amongst others the batch equilibration and equilibrium soil solution methods. According to the USEPA (1999), the former represents the most common laboratory method for determining partition coefficients—normally defined as Kd—both for contaminated sites studies and for predictions of chemicals behaviour in soils (OECD, 2002). The batch equilibration method consists of mixing a soil with a known amount of liquid (background electrolyte), which is then shaken into a slurry and allowed to equilibrate for an adequate time. The solution will be separated from the solids by centrifuging the slurry, resulting in a supernatant and a separated solid phase. The supernatant will, therefore, be removed, filtered and analysed. 

For gaseous samples in the temperature region from 0 to 40 °C the partition coefficient normally increases by a factor 2 - 4 if the temperature decreases about 20 °C. Generally, aqueous samples show much weaker dependence on temperature and the sign is often not predictable. 

Although they are of the same general order of magnitude, the values for Koc tabulated in Table I exhibit a fairly wide range of variability. Partition coefficients normalized to the organic carbon mass fraction of one particular set of soils or sediments may therefore not be appropriate for other soils and sediments. Restrictions to the application of such coefficients have been demonstrated, for example, for soils having natural organic matter mass fractions below/oc = 0.001 (6, 7). 

An overview of some basic mathematical techniques for data correlation is to be found herein together with background on several types of physical property correlating techniques and a road map for the use of selected methods. Methods are presented for the correlation of observed experimental data to physical properties such as critical properties, normal boiling point, molar volume, vapor pressure, heats of vaporization and fusion, heat capacity, surface tension, viscosity, thermal conductivity, acentric factor, flammability limits, enthalpy of formation, Gibbs energy, entropy, activity coefficients, Henry s constant, octanol—water partition coefficients, diffusion coefficients, virial coefficients, chemical reactivity, and toxicological parameters. 

To further analyze the relationships within descriptor space we performed a principle component analysis of the whole data matrix. Descriptors have been normalized before the analysis to have a mean of 0 and standard deviation of 1. The first two principal components explain 78% of variance within the data. The resultant loadings, which characterize contributions of the original descriptors to these principal components, are shown on Fig. 5.8. On the plot we can see that PSA, Hhed and Uhba are indeed closely grouped together. Calculated octanol-water partition coefficient CLOGP is located in the opposite corner of the property space. This analysis also demonstrates that CLOGP and PSA are the two parameters with... 

Water solubility, dissociation constant(s) and n-octanol/water partition coefficients allow one to predict how an analyte may behave on normal-phase (NP), reversed-phase (RP), or ion-exchange solid-phase extraction (SPE) for sample enrichment and cleanup. 

In this chapter, the voltammetric study of local anesthetics (procaine and related compounds) [14—16], antihistamines (doxylamine and related compounds) [17,22], and uncouplers (2,4-dinitrophenol and related compounds) [18] at nitrobenzene (NB]Uwater (W) and 1,2-dichloroethane (DCE)-water (W) interfaces is discussed. Potential step voltammetry (chronoamperometry) or normal pulse voltammetry (NPV) and potential sweep voltammetry or cyclic voltammetry (CV) have been employed. Theoretical equations of the half-wave potential vs. pH diagram are derived and applied to interpret the midpoint potential or half-wave potential vs. pH plots to evaluate physicochemical properties, including the partition coefficients and dissociation constants of the drugs. Voltammetric study of the kinetics of protonation of base (procaine) in aqueous solution is also discussed. Finally, application to structure-activity relationship and mode of action study will be discussed briefly. 

Unfortunately, appears slightly larger than the radius of Ba, which makes one limb of the parabola poorly constrained. Moreover, typically only three divalent partition coefficients are measured (Ba, Sr and Ca), and Dca, when analyzed by EMPA, is normally imprecise. We have taken an alternative approach, using 1+ partitioning data to constrain and, which are then converted to and, using some of the simple relationships described above. The data of Icenhower and London (1995) are ideal for this purpose as they report partition coefficients for Na, K, Rb and Cs, which span the size of the X site. For 15 experiments at 650-750°C and 0.2 GPa, we obtain a very tight cluster of (1.650-1.673 A) and (47-56 GPa), with mean values of... 

MHE can be used for substances of high volatility with a small partition coefficient. Method is based on a stepwise gas extraction at equal time intervals. Normal headspace chromatogram is run, a fraction of the gas phase exhausted, and a second headspace chromatogram is run. -The difference in petUc areas provides a measure of the total peak area of the analyte. 

P Partition coefficient (of drug) between normal octanol and water... 

Oxidizing Chemical Air-Water Partition Coefficient (Atm 20°C) Relative Volatility (Normalized)... 

Sorption. Capture of neutral organics by non-living particulates depends on the organic carbon content of the solids (9). Equilibrium sorption of such "hydrophobic" compounds can be described by a carbon-normalized partition coefficient on both a whole-sediment basis and by particle size classes. The success of the whole-sediment approach derives from the fact that most natural sediment organic matter falls in the "silt" or "fine" particle size fractions. So long as dissolved concentrations do not exceed 0.01 mM, linear isotherms (partition coefficients) can be used. At higher concentrations, the sorptive capacity of the solid can be exceeded, and a nonlinear Freundlich or Langmuir isotherm must be invoked. 

In lc there are other sorption mechanisms that can cause separation, depending on whether we choose to use a liquid or a solid as the stationary phase, or what kind of solid we use. Liquid-liquid chromatography (11c) uses a liquid stationary phase coated onto a finely divided inert solid support. Separation here is due to differences in the partition coefficients of solutes between the stationary liquid and the liquid mobile phase. In normal phase 11c the stationary phase is relatively polar and the mobile phase relatively non-polar, whilst... 

Another method of predicting human pharmacokinetics is physiologically based pharmacokinetics (PB-PK). The normal pharmacokinetic approach is to try to fit the plasma concentration-time curve to a mathematical function with one, two or three compartments, which are really mathematical constructs necessary for curve fitting, and do not necessarily have any physiological correlates. In PB-PK, the model consists of a series of compartments that are taken to actually represent different tissues [75-77] (Fig. 6.3). In order to build the model it is necessary to know the size and perfusion rate of each tissue, the partition coefficient of the compound between each tissue and blood, and the rate of clearance of the compound in each tissue. Although different sources of errors in the models have been... 

The Level I calculation suggests that if 100,000 kg (100 tonnes) of benzene are introduced into the 100,000 km2 environment, 99% will partition into air at a concentration of 9.9 x 10-7 g/m3 or about 1 pg/rn3. The water will contain nearly 1% at a low concentration of 4 pg/rn3 or equivalently 4 ng/L. Soils would contain 5 x 10-6 pg/g and sediments about 9.7 x 10 6 pg/g. These values would normally be undetectable as a result of the very low tendency of benzene to sorb to organic matter in these media. The fugacity is calculated to be 3.14 x 10-5 Pa. The dimensionless soil-water and sediment-water partition coefficients or ratios of Z values are 2.6 and 5.3 as a result of a Koc of about 55 and a few percent organic carbon in these media. There is little evidence of bioconcentration with a very low fish concentration of 3.0 x FT5 pg/g. The pie chart in Figure 1.7.6 clearly shows that air is the primary medium of accumulation. 

Jonsson, J. A., Vejrosta, J., Novak, J. (1982) Air/water partition coefficients for normal alkanes (n-pentane to n-nonane). Fluid Phase Equil. 9, 279-286. 

Basak, S. C., Gute, B. D., and Grunwald, G. D. A comparative study of topological and geometrical parameters in estimating normal boiling point and octanol-water partition coefficient. J. Chem. Inf. Comput. Sci. 1996, 36, 1054—1060. 

The Uj and w, deviates are normal deviates, the deviates vf are log-normal. See text for the description of the computed random variables K represents mineral-liquid partition coefficients, F the fraction of residual melt, x the fraction of a mineral in the cumulate, D bulk solid-liquid partition coefficients. 

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