Shake-flask method water solubility determination

Groves, F., Jr. Solubility of cycloparaffins in distilled water and saltwater, J. Chem. Eng. Data, 33 (2) 136-138, 1988. Grunewald, G.L., Pleiss, M.A., Gatchell, C.L., Pazhenchevsky, R., and Rafferty, M.F. Gas chromatographic quantitation of underivatized amines in the determination of their octanol-0.1 Msodium hydroxide partition coefficients by the shake-flask method, J. Chromatogr. A, 292(2) 319-331, 1984. 

The basic principle of the method is to measure the dissolution of the substance in two different phases, water and -octanol. In order to determine the partition coefficient, equilibrium between all interacting components of the system must be achieved after which the concentration of the substances dissolved in the two phases is determined. The shake-flask method is applicable when the log Kow value falls within the range from -2 to 4 (OECD 107, 1995). The shake-flask method applies only to essential pure substances soluble in water and -octanol and should be performed at a constant temperature ( 1°C) in the range 20-25 °C. 

Accurate values of Pow are clearly necessary for the ultimate calibration of all surrogate systems, but, in practice, direct measurements of Powby the traditional shake-flask method are seldom used. Particularly for compounds with low water solubility, experimental difficulties may arise from problems in phase separation without carryover, sorption to glass surfaces, or from formation of emulsions. All of these introduce serious uncertainties into the concentrations in the appropriate phases, and may consequently lead to substantial errors in the estimates of partition coefficients. The problem is particularly acute for compounds with extremely low solubility in water such as the chlorinated dibenzo[l,4]dioxins for which widely varying values have been reported (Marple et al. 1986 Shiu et al. 1988). For such compounds, use of a generator column has been advocated (De Voe et al. 1981 Woodburn et al. 1984). In essence, the following steps are carried out (1) a solution of the test substance in octanol is equilibrated with water and the concentration in the octanol phase is determined, (2) the octanol phase is... 

Kov, of a number of pesticides, including OCPs, are reported in a paper by Finizio et al. who determined values by means of three different estimation methods, including calculation from water solubility, then compared the obtained results with experimental values measured with Slow Stirring or Shake Flask methods. 

The experimental approaches are similar to those for solubility, i.e., employing shake flask or generator-column techniques. Concentrations in both the water and octanol phases may be determined after equilibration. Both phases can then be analyzed by the instrumental methods discussed above and the partition coefficient is calculated from the concentration ratio Q/Cw. This is actually the ratio of solute concentration in octanol saturated with water to that in water saturated with octanol. 

Sutton and Calder (9) have also measured the solubilities of several alkylbenzenes in distilled water and in seawater by a method based on GC. Saturated solutions were prepared by equilibrating water with aromatic vapor in an all-glass apparatus consisting of a 1-L Erlenmeyer flask with an insert tube. The insert tube was used to store the compound. It was capped with a ground-glass stopper. The liquid hydrocarbon did not come into contact with the water except through a perforation in the insert, which allowed hydrocarbon vapors to enter the headspace above the water in the flask. The flask was placed in a constant-temperature shaking bath controlled at 25.0 dt 0.1°C. The water was equilibrated for 48 hr prior to analysis. The solubilities were determined by solvent extraction of the saturated solutions with subsequent analyses of the extracts by GC. 

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