Partition coefficient shake-flask

Partition coefficient Shake flask Acceptable although extreme values present experiment difficulties... 

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. 

However, as stated above, the partition coefficients measured by the shake-flask method or by potenhometric titration can be influenced by the potenhal difference between the two phases, and are therefore apparent values which depend on the experimental condihons (phase volume ratio, nature and concentrahons of all ions in the solutions). In particular, it has been shown that the difference between the apparent and the standard log Pi depends on the phase volume raho and that this relationship itself depends on the lipophilicity of the ion [80]. In theory, the most relevant case for in vivo extrapolation is when V /V 1 as it corresponds to the phase ratio encountered by a drug as it distributes within the body. The measurement of apparent log Pi values does not allow to differentiate between ion-pairing effect and partihoning of the ions due to the Galvani potential difference, and it has been shown that the apparent lipophilicity of a number of quaternary ion drugs is not due to ion-pair partitioning as inihally thought [80]. 

Niflumic acid, which has two pKa values, was studied both pH-metrically and spectroscopically using the shake-flask method [224]. The monoprotonated species can exist in two forms (1) zwitterion, XH 1 and (2) ordinary (uncharged) ampholyte, XH°. The ratio between the two forms (tautomeric ratio) was measured spectroscopically to be 17.4. On assuming that a negligible amount of zwitterion XH partitions into octanol, the calculated micro-log/1 for XH° was 5.1, quite a bit higher than the macro-log/1 3.9 determined pH-metrically in 0.15 M NaCl. It is noteworthy that the distribution coefficient D is the same regardless of whether the species are described with microconstants or macroconstants [275]. 

Slater, B. McCormack, A. Avdeef, A. Comer, J. E. A., pH-metric logP. 4. Comparison of partition coefficients determined by shake-flask, hplc and potentiometric methods, J. Pharm. Sci. 83, 1280-1283 (1994). 

Comparison of partition coefficients determined by shake-flask, HPLC and potentiometric methods, J. Pharm. Sci. 1994, 83, 1280-1283. 

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. 

Data collected with a simple RPLC procedure has been found to be in good agreement with 1-octanol shake-flask partition or distribution coefficients over a 3.5 log range [64], A chemically bonded octadecylsilane support is coated with 1-octanol. With 1-octanol-saturated buffers as mobile phases, a stable baseline (compared to 1-octanol absorbed on silica) is... 

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. 

Han, S. D., Park, S. J., and Park, S.-J. Determination of octanol/water partition coefficients by nsing a shake-flask method,... 

Paschke, A., Neitzel, P.E., Walther, W., and Schiirmann, G. Octanol/water partition coefficient of selected herbicides determination using shake-flask method and reversed-phase high-performance liquid chromatography, J. Chem. Eng. Data, 49(6) 1639-1642, 2004. 

Xie, T.M., Hulthe, B and Folestad, S. Determination of partition coefficients of chlorinated phenols, guaiacols and catechols by shake-flask GC and HPLC, Chemosphere, 13(3) 445-459, 1984. 

While applications and analysis of ILs may provide some guidance on potential applications of SCIL-based phases in EC, these phases may also provide useful information about ILs. As Poole points out [16], a key requirement for the successful integration of ILs in industrial processes is the ability of being applied to rapid liquid-liquid phase separation systems. Shake-flask methods are commonly used to measure IL/water partition coefficients. However, the high viscosity and cost of these materials coupled with the time and effort required for traditional shake-flask methods render this... 

The octanol-water (pH 5) partition coefficients of alkyl-substituted 4H-pyrido[l,2-a]pyrimidines-4-ones 10 and 11, 3-phenyl and 3-ester derivatives (R2 = Ph, COOEt), and some tetra- and hexahydro derivatives were determined by the classical shake-flask technique at ambient temperature (81MI4 82MI9). Hansch-type 7r values of the substituent (R-R2) were also calculated. The apparent octanol-water partition coefficients of seg-anserine 6 and its 7-methyl derivative were measured (88MI14). The pAa values and apparent octanol-water partition coefficients (at pH 7.4) of risperidone 7 (92MI20, 92MI30), its 9-hydroxy derivative (92MI30), and ocaperidone 8 were reported (92MI20). 

Centrifugal Partition Chromatography (CPC) has been shown to yield partition coefficients which compare quite favorably with those measured by traditional shake-flask (El Tayar, 1993). The procedure, which employs a coil planet type centrifuge in a horizontal flow-through system, has been described (El Tayar, 1991) The equipment can handle organic solvents with low viscosity (such as heptane) more readily than it handles octanol, but log octanol/water values in the range of -3.0 to +3.0 seem reliable. It has been used quite effectively in measuring the log Ps of amino adds (Tsai, 1991). 

Microemulsion electrokinetic chromatography, MEEKC (or MECC), is a relatively new technique which holds some promise of delivering octanol/water partition coefficients much more conveniently than the shake-flask method (Gluck, 1996 Ishihama, 1994). MEEKC is claimed to have all the advantages of an HPLC method but it is not suitable for solutes with pKas much below 7.0 (Adlard, 1995). It has been used over a log P range of -1.0 to +4.0. 

Mirrlees MS, Moulton SJ, Murphy CT et al. (1976) Direct measurement of octanol-water partition coefficients by high-pressure liquid chromatography. J Med Chem 19 615-619 Pagliara A, Khamis E, Thrinh A et al. (1995) Structural properties governing retention mechanisms on RP-HPLC stationary phases used for lipophilicity measurements. J Liquid Chromatography 18 1721-1745 Slater B, McCormack A, Avdeef A et al. (1994) pH-Metric log P. 4. Comparison of Partition Coefficients Determined by Shake-Flask, HPLC and Potentiometric Methods. J Phar-maceut Sci 83 1280-1283... 

The partition coefficient logP or the distribution coefficient logD between water and n-octanol are determined traditionally by the shake flask method (see chapter about physicochemical parameters). The shake flask method is a rather labour intensive method and not suited for high throughput analysis needed in pharmaceutical research. 

However, there are obvious differences between the classically determined octanol-water partition data and the reversed phase chromatographic partition data due to the different nature of the partitioning solvents. The correlation between shake flask octanol water partition coefficients and chromatographic retention factor kw (0 % organic solvent) was described to be low (Valko 2004) when structurally diverse compound sets were analysed. Using the q>o or the CHI lipophilicity index an improvement in agreement to logPow was reported (Valko 1993,1997). 

However, related to drug absorption, both classical octanol-water partition coefficients and chromatographic partition coefficients using the different chromatographic scales have shown to be predictive. If the exact octanol-water partitioning behaviour of a solute has to be analysed the reversed phase chromatographic experiments seem to be no substitute for classical shake flask experiments. For comparison... 

The classical measurement of LogP is the shake flask method [17]. A known amount of drug is dissolved in a flask containing both octanol phase and aqueous buffer at controlled pH to ensure the existence of only nonionic form (at least two units from the drug pA) ). The flask is shaken to equilibrate the sample between two phases. There must be no undissolved substance present in both phases. After the system reaches its equilibrium, which is time- and temperature-dependent, the concentration of drug is analyzed by HPLC in both phases. Partitioning coefficient is calculated as... 

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