Correlation equations, estimation partition coefficients

The following correlation equations were used in the estimation of partition coefficients used in this paper. 

Residence time and reactivity are strongly correlated through equation (7.2.9). This is true for seawater composition since Whitfield and Turner (1979) showed a rather good correlation between oceanic residence times and seawater-crustal rock partition coefficients which are taken as a measure of element reactivity in the ocean. Actually, a better estimate of reactivity is given by oceanic suspensions, so Li (1982) suggested to use pelagic clay-seawater concentration ratios as a proxy to partition coefficients. 

The substance-specific kinetic constants, kx and k2, and partition coefficient Ksw (see Equations 3.1 and 3.2) can be determined in two ways. In theory, kinetic parameters characterizing the uptake of analytes can be estimated using semiempirical correlations employing mass transfer coefficients, physicochemical properties (mainly diffusivities and permeabilities in various media), and hydro-dynamic parameters.38 39 However, because of the complexity of the flow of water around passive sampling devices (usually nonstreamlined objects) during field exposures, it is difficult to estimate uptake parameters from first principles. In most cases, laboratory experiments are needed for the calibration of both equilibrium and kinetic samplers. 

Several laboratories have measured solubilities and/or partition coefficients of solutes in higher molecular weight media, and their data provides a test of this approach to estimating polymer solubilities. Flynn and Yalkowsky (17,18) studied the transport and solubility properties of a series of p-aminobenzoate esters, p-HjNCjH COOR, R = methyl to hexyl, in poly(dimethylsiloxane) fluid (PDMS). We find that their values of log P(PDMS) correlate well with reported (33) values of log P values of the same series of solutes in oleyl alcohol/water, as illustrated by the plot in Figure 8 and the correlation statistics (Equation 17). 

Equation 6 is very useful for estimating changes in the partition coefficient as well as changes in the herbicidal activity of para-substituted TFMS compounds (see below) produced when 0.1% Tween 80 is added to the herbicidal formulations. An expression analogous to Equation 6 can be derived from Equation 5b for meta-substituted TFMS series members although the predictive utility of this latter equation will obviously be limited by the lesser degree of correlation between an(l X ... 

Compilations of infinite-dilution activity coefficients, when available for the solute of interest, may be used to rank candidate solvents. Partition ratios at finite concentrations can be estimated from these data by extrapolation from infinite dilution using a suitable correlation equation such as NRTL [Eq. (15-25)]. Examples of these lands of calculations are given by Walas [Phase EquU ria in Chemical Engineering (Butterworth-Heinemann, 1985)]. Most activity coefficients available in the literature are for small organic molecules and are derived from vapor-liquid equilibrium measurements or azeotropic composition data. 

If BCF is not available from experimental measurements, it can be estimated via correlation equations from water solubility (S), octanol-water partition coefficient (KQw) or soil adsorption coefficient (Koc). Of the three, correlations from Kow are considered the most reliable because they are currently based on the largest body of bioassay data and because measurements involve a water-lipophilic phase partitioning which bears obvious similarity to water-to-fish partitioning. One recommended correlation equation is (11) ... 

Partition chromatography, as its name suggests, is dependent on distribution law. Bate-Smith and Westall [60] have shown that values are related to distribution coefficients through Equations (44) and (45). a is the distribution coefficient between mobile and stationary phases and k is a constant, dependent on the ratio of the volumes of stationary and mobile phases. values have been used to estimate distribution coefficients [61] and in correlations with the biological activities of penicillins [62] and of androgens [63,64]... 

The suspended sediment/water partition coefficients have been measured for 19 chlorinated organics in 25 samples from the St. Clair, Detroit and Niagara Rivers. An excellent linear correlation (r = 0.87) between the organic-carbon corrected partition coefficient (Kqq) and the octanol/water partition coefficient (Kq, ) was found (log = 0.76 log + 1.66). Using this equation plus another equation developed in this paper it is shown that the percentage of chemical in the dissolved and particulate phases in the study rivers could be estimated from a chemical s to within a factor of two. The paper also discusses the time required for equilibrium to be achieved between the dissolved and particulate phases, and the potential importance of biota such as algae in the partitioning process. 

Two compounds had to be excluded from the data set. They were outliers (1.3 log units deviation) as also found in the analysis by Abraham et al. [26], It must also be remembered when considering the derived equations that log BB is a complex parameter that encompasses brain partitioning and permeability and may also depend on other processes such as metabolism, active transport, and so forth. Thus, the standard deviations of these determinations may fall within the range of the mean values. The authors could demonstrate that the derived equation could also estimate log BB outside of the training data set. Therefore, the value of the above correlation with the solvation free energy lies in its power to rank compounds for their ability to cross the blood-brain barrier before synthesis. Interestingly, it was also shown by Lombardo et al. [71] that the calculated AG°W correlated well with the determined permeability coefficient, PC, using endothelial cell monolayers from bovine brain mi-... 

In conclusion, the solvation equation could be applied to describe several liquid chromatographic partition systems in terms of their sensitivity towards molecular properties. The standard error for estimating the retention data was low and the multiple correlation coefficients of the solvation equations were high. The parameters of the solvation equations help us to understand and describe the different selectivity of the stationary phases, and also to understand the retention of the compounds in a given system based on its molecular properties. 

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