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True partition coefficient

In the traditional shake-flask method, the apparent partition coefficient, log D, is measured, usually at pH 7.4 (sometimes at pH 6.5). Different buffers are used to control each pH used in the determinations [70]. Usually, in a comprehensive study, several pH measurements are made, and values of log are plotted against the pH. This plot is often called the lipophilicity profile . One can determine the true partition coefficients (log P ) and the ionization constants from the features in such a curve. [Pg.65]

The membrane permeabilities Pm may be converted to intrinsic permeabilities P(h when the pKa is taken into consideration. An ionizable molecule exhibits its intrinsic permeability when it is in its uncharged form and there is no water layer resistance. The relationship between Pm and P0 is like that between the pH-dependent apparent partition coefficient (log Kd) and the true partition coefficient (log Kp), respectively. This relationship can be rationalized by the mass balance. Take, for example, the case of a monoprotic acid, HA. The total substance concentration is... [Pg.200]

Takacs-Novak, K. Jozan, M. Szasz, G., Lipophilicity of amphoteric molecules expressed by the true partition coefficient, Int. J. Pharm. 113, 47 (1995). [Pg.263]

A series of experiments was also conducted by Bowman et al. [34] to ascertain the effects of differing environmental factors on the sediment-water interactions of natural estrogens (estradiol and estrone) under estuarine conditions. Sorption onto sediment particles was in this case relatively slow, with sorption equilibrium being reached in about 10 and 170 h for estrone and estradiol, respectively. On the other hand, true partition coefficients calculated on colloids were found to be around two orders of magnitude greater that those on sediment particles. Hence, it was concluded that under estuarine conditions, and in comparison to other more hydrophobic compounds, both estrone and estradiol... [Pg.8]

Ezumi, K. and Kubota, T. Simultaneous determination of acid dissociation constants and true partition coefficients by analyses of the apparent partition coefficient, Chem. Pharm. Bull, 28(1) 85-91, 1980. [Pg.1655]

The constant Xav, is not a true partition coefficient because of difference, Vt — V0> includes the solids and the fluid associated with the gel or stationary phase. By definition, V represents only the fluid inside the stationary-phase particles and does not include the volume occupied by the solids which make up the gel. Thus Xav is a property of the gel, and like Kd it defines solute behavior independently of the bed dimensions. The ratio of to Kd should be a constant for a given gel packed in a specific column (34). [Pg.52]

Takacs-Novak, K., M. Jozan, and G. Szasz. 1995. Lipophilicity of Amphoteric Molecules Expressed by the True Partition Coefficient. Intern. J. Pharmaceut. 113, 47-55. [Pg.133]

Equation (3.110) is more direct than Equation (3.115). An advantage of Equation (3.115) is that it is not necessary to analyze the concentration of the weak acid in the oil phase. Figure 3.19 shows the effect of the pH on the partition coefficient of a slightly soluble weak acid (i.e., salicylic acid). The apparent partition coefficient becomes the true partition coefficient when the weak acid is essentially in the unionized form (low pH). [Pg.174]

Another important factor is the influence of drug ionization on the partition coefficient and this is particularly important when a buffer is used instead of water. The partition coefficient determined from Equation (14) is an apparent value rather than a true partition coefficient for ionic drugs. However, the true partition coefficient can be calculated from the apparent partition coefficient if the drug s pA a and the pH of the drug solution are known [39], as shown in the equations... [Pg.957]

Apparent versus True Partition Coefficient (iog P versus iog P)... [Pg.2596]

If a solute is ionizable (either acidic or basic), two different species can exist in the aqueous phase, and therefore the apparent partition coefficient (P ) or the true partition coefficients (P) can be measured, as shown below and in Eqs. (11)-(15)... [Pg.2596]

The partition coefficient of the unionised drug (the true partition coefficient) should remain constant and is given by... [Pg.32]

Q2.1 Explain the difference between the true partition coefficient and the apparent partition coefficient. [Pg.56]

Outline how the true partition coefficient of a sparingly water-soluble drug such as sulfamethoxazole might conveniently be measured (see Figure 2.13). [Pg.56]

The true partition coefficient is the partition coefficient for the unionised molecule. [Pg.254]

The true partition coefficient between soil and water = CJ CJ where Q and are the concentrations in soil and water, respectively) depends on the amoimt of organic carbon in the soU. Thus can be calculated as ... [Pg.89]

Thus, the constant Kp is a true partition coefficient and its existence reveals the equality between the chemical potentials of OH in the two phases ... [Pg.679]


See other pages where True partition coefficient is mentioned: [Pg.415]    [Pg.44]    [Pg.31]    [Pg.123]    [Pg.359]    [Pg.3648]    [Pg.462]   
See also in sourсe #XX -- [ Pg.31 , Pg.56 , Pg.256 ]




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