Partition measurement

TABLE 32.2 Standard Gibbs Energy of Transfer and Standard Ion Transfer Potentials for Ion Transfer Between Water and Nitrobenzene Derived from Partition Measurements... 

Seventy years later, this theory largely holds true, although periodically challenged [67, 68]. Observation of transmembrane permeability of ionic species was initially explained by the formation of neutral ion-pair [69, 70]. A comprehensive review of the physicochemical properties influencing permeation has been written by Malkia et al. [5]. The reality is that, despite many studies, the effect of ionization on permeation is still a matter of discussion and active research. In contrast, it became clear that bulk-phase partitioning measurements are not adequate to describe bilayer partitioning [71-73]. 

Fig. 16. Text of the Debye-Huckel law and evaluation of for the partition measure-...

Measurements of this type were carried out for the methylbenzene-(HF -h BFg) system at 0°C by MacCaulay and Lien (1951). However, the authors used the method only in order to demonstrate the formation of the proton addition complex. They used partition measurements to determine the basicity. 

This chapter gives an overview of the experimental and modelling approaches which commonly are used to estimate the particle/gas distribution of POPs in air. More detailed reviews appear in a recent book devoted to gas and particle partitioning measurements (Lane, 1999). 

Lane, D.A., 1999. Gas and Particle Phase Partition Measurements of Atmospheric Organic Compounds. Gordon and Breach Publishers, in press. 

Rl/+X from w to o, a s are the mean activities, y s are the mean activity coefficients, and cRX s are the equilibrium electrolyte concentrations. A non-thermodynamic assumption has to be introduced to construct the scale of the inner (Galvani) potential differences from the partition measurements. The most commonly used hypothesis is that the tetraphenylarsonium cation (Ph4As+) and the tetraphenylborate anion (PI14 B ) have equal standard Gibbs energies of transfer for any combination of two solvents [iv]. This assumption enables the evaluation of AG 1 and AG j from the partition mea-... 

P values of 0.87, 0.024 and 0.32 for the cation, zwitterion and anion respectively were calculated from pKa values and partition measurements into iso-butanol over the pH range 1 to 9.5 [12]. 

Takacsne Novak K. Practical aspects of partition measurements according to GLP rule. Acta Pharm Hung 1997 Sep 67(5) 179-191. 

Furthermore, in many cases the effect of the third component, namely the solvent, is decisive. For example, the measured Henry s law constant for the system aromatic substance-HCl, only reflects the difference between the chemical potential of HCl in solution, and in the vapour phase, p% (Kortiim and Vogel, 1955). The values obtained therefore do not permit a quantitative interpretation and only give qualitatively the relative order of the basicity of unsaturated compounds. This is also true for partition measurements between an acid and an organic phase, if in such a case the necessary thermodynamic assumptions have not been tested or established by separate investigations. 

Results of our soil partition measurements are collected in Table VIII. 

Although from a wave-mechanical viewpoint, the radius of an individual ion has no precise physical significance, for purposes of descriptive crystallography, it is convenient to have a compilation of values obtained by partitioning measured interatomic distances in ionic compounds. Values of the ionic radius (/-jon) may be derived from X-ray diffraction data. However, experimental data only give the internuclear distance and we generally take this to be the sum of the ionic radii of the cation and anion (equation 5.6). 

Values of AG° may also be obtained by partition measurements of the solute between pairs of immiscible solvent, but this method of course is restricted in terms of solvents. In all investigations of AG° values, it is necessary to specify the concentration units employed, and to ensure that in the basic equations and the concentration units of the rate constant (for second-order constants) are the same as those used in the calculation of the AG° values. In the present paper, the concentration units in solution will be mol fractions, and all second-order rate constants will be corrected to units of (mol fraction) s before calculation of the 5AG values(34). 

HX) are created in 10% of the collisions for the HQ case and 20% for the HBr case [86]. For the purely singlet reactions, producing OH(2]T) + H(2s), energy partitioning measurements [87-89] indicate that the internal excitation of the product molecule is very large. The OH rotational distribution in the lowest vibrational levels (the only ones which have been measured to date) is inverted. This may not carry any dynamical information, however, as it is possibly the result of simple angular momentum constraints. (See Ref, 63 and Refs. 90-93 for a discussion of this in the case of the H2 reaction). 

Tihminlioglu, F., Surana, R.K., Danner, R.P., and Duda, J.L. (1997) Finite concentration inverse gas chromatography Diffusion and partition measurements. 

The environmental parameters and physico-chemical properties included in the bench-mark concept are aqueous solubility, vapor pressure, aqueous hydrolysis, sorption-desorption, biotic and abiotic transformations, and partitioning measured under standard conditions. Chemicals with high log Pqw and high environmental persistence value will be flagged for their potential toxicity through bioaccumulation and relatively long periods of exposure to humans and the environment, respectively. Figure 11.6 shows a hypothetical environmental profile of a chemical that could be used to predict its behavior with time. Further development is needed for field data, validation, and extension of the concept to effects and toxicity pattern. 

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