Pure compound-water partitioning

Boublik, T., Fried, V., Hala, E. (1984) The Vapor Pressure of Pure Substances, 2nd revised Edition, Elsevier, Amsterdam, The Netherlands. Bowman, B. T., Sans, W. W. (1983) Determination of octanol-water partitioning coefficient (KqW) of 61 organophosphorus and carbamate insecticides and their relationship to respective water solubility (S) values. J. Environ. Sci. Health B18, 667-683. Bradley, R. S., Cleasby, T. G. (1953) The vapour pressure and lattice energy of some aromatic ring compounds. J. Chem. Soc. 1953, 1690-1692. 

The partitioning exhibited through the Henry s Law constant can be used to estimate the vaporization of various PCB contaminants from solid surfaces. In the presence of water, organic compounds volatilize more rapidly than would be expected based upon vaporization of the pure compound. This tendency accounts for the presence of low vapor pressure contaminants, such as the PCBs, in the atmosphere at higher concentrations than one would estimate from the chemistry of the pure compounds [403,408,409]... 

Two retention indices are then measured, log kgs (log k obtained with a mobile phase containing 95% of acetonitrile and 5% of buffer solution) and log ko (retention factor obtained with a pure aqueous mobile phase). The difference between these two values (log ko 9s) is correlated to the 1-octanol/water partition coefficient of the neutral form of tested compounds (Equation 5.13) ... 

Alternatively, solvent partition or countercurrent techniques may be applied. In order to obtain an isoflavonoid-rich fraction from Erythrina species (Leguminosae) for further purification work, an organic solvent extract was dissolved in 90% methanol and first partitioned with hexane. The residual methanol part was adjusted with water to 30% and partitioned with t-butyl methyl ether-hexane (9 1). This latter mixture was then chromatographed to obtain pure compounds. ... 

Octanol-water partition constant and aqueous solubility of the pure liquid compound l°g - iow = -a- logCf + b 7... 

We will start our discussion by considering a special case, that is, the situation in which the molecules of a pure compound (gas, liquid, or solid) are partitioned so that its concentration reflects equilibrium between the pure material and aqueous solution. In this case, we refer to the equilibrium concentration (or the saturation concentration) in the aqueous phase as the water solubility or the aqueous solubility of the compound. This concentration will be denoted as Qf. This compound property, which has been determined experimentally for many compounds, tells us the maximum concentration of a given chemical that can be dissolved in pure water at a given temperature. In Section 5.2, we will discuss how the aqueous activity coefficient at saturation, y, , is related to aqueous solubility. We will also examine when we can use yf as the activity coefficient of a compound in diluted aqueous solution, y (which represents a more relevant situation in the environment). 

Several studies have shown that the concentrations of many organic pollutants in fog water are much higher than would be expected from the compound s equilibrium air/ water partition constant (see Chapter 6), Kiaw (= gaseous concentration of compound i in the air/dissolved concentration of compound i in pure bulk water). In order to describe the observed enrichment of compounds in fog water, an enrichment factor EF can be defined (see Goss, 1994 and references cited therein) ... 

A standard methodology was used for the fractionation of these. Thus, the MeOH extract of aerial parts of B. rigidum was partitioned between n-BuOH and water. The w-BuOH soluble fraction was chromatographed over a silica gel column, followed by repeated MPLC purification to give seven pure compounds. 

It is important to note that the partitioning behavior of organic compounds is affected by the presence of other hydrocarbons in the subsurface. The maximum dissolved concentrations achieved in the subsurface are always less than the concentration of any pure compound, when it is present as one of many constituents of a petroleum product (ASTM 1995). For example, the solubility of pure benzene in water is given as 1,780 mg/L, but the maximum calculated concentration in an aquifer immediately beneath a gasoline release has been estimated to be about 62 mg/L (Daugherty 1991). 

This relationship indicates that permeation across membranes is significantly determined by the respective lipid/water partition coefficients of the compounds. If significant interactions between the chemical and the membrane occur (e.g. hydrogen bonding), the transfer across the membrane may be slower than indicated from pure diffusion. The differences in properties of the lipid phases give rise to unequal distribution among, for example, body tissues and liquids. The resultant equilibrium concentrations are a function of both the biotic/abiotic system and the chemicals investigated. Hence, the... 

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