Partition coefficient chromatographic techniques

Menges, R.A., Bertrand, G.L., and Armstrong, D.W. Direct measurement of octanol-water partition coefficient chromatograph with a back-flushing technique, / Liq. Chromatogr., 13(15) 3061-3077, 1990. 

El Tayar, N. Tsai, R.-S. Vallat, P. Altomare, C. Testa, B., Measurement of partition coefficients by various centrifugal partition chromatographic techniques. A comparative evaluation, J. Chromatogr. 556, 181-194 (1991). 

Wang, X. and Song, H. Determination of octanol-water partition coefficients of organic pollutants by using the dynamic coupled-column liquid chromatographic technique, Trans. Tianjin Univ, 2(l) 59-63, 1996. 

Various countercurrent chromatographic techniques have been successfully employed for the separation of flavonoids. Countercurrent chromatography is a separation technique that relies on the partition of a sample between two immiscible solvents, the relative proportions of solute passing into each of the two phases determined by the partition coefficients of the components of the solute. It is an all-liquid method that is characterized by the absence of a solid support, and thus has the following advantages over other chromatographic techniques ... 

The usefulness of the LSER approach hinges on the similarity of the partitioning coefficients obtained from the sensing experiments (Ks) and the gas chromatographic experiments (Kqc)- In other words, it is assumed that the relationship Ks Kgc holds. This is how LSER is used for evaluation of a new sensing material. First, the coefficient Kqc is obtained from the tabulated database or experimentally. Second, the multiple linear regression technique (see Chapter 10) is used to obtain the best fit for the sensor test data, and the individual coefficients in (2.3) are evaluated. This approach has been used successfully in evaluation of multiple materials for gas sensors (Abraham et al., 1995 Grate et al., 1996). 

El Tayar, N., R.-S. Tsai, P. Vallat, C. Altomare, and B. Testa. 1991. Measurement of Partition Coefficients by Various Centrifuge Partition Chromatographic Techniques A Comparative Evaluation. /. Chromatog. 556 181-194. 

Since the evaluation of this parameter is very important, it was also measured using the micellar HPLC technique (9), which allows a better estimation of the partition coefficients in the presence of quite high concentrations of surfactant. The chromatographic parameter P was measured for each ligand as a function of surfactant concentration, according to Equation 2 ... 

The more traditional approach is to use the chromatographic technique for the concentration determination necessary to derive physico-chemical properties for example, measuring the equilibrium concentration of compounds in a saturated solution for solubility measurements, or measuring the distribution concentration in two immiscible solvents for the determination of partition coefficients. Both approaches can be used for lipophilicity determinations and will be fully discussed in this chapter. 

The purpose of this review is to summarize the conditions used to derive chromatographic lipophilicity indices, to appraise associated difficulties, and to provide an overview of their relation with octanol-water partition coefficients. In this aspect, both techniques will be discussed in parallel. 

Q.26.14 (a) Define partition coefficient ratio, theoretical plate, and retention time, b) Choose a protein property (size, or charge, etc.) and describe the liquid-solid chromatographic technique you would use to separate it. Draw the device, labeling the essential parts needed for separation. 

The forced migration of a liquid phase in continuous contact with a stationary phase is encountered in several chromatographic techniques. One of the aspects particular to HPLC is that of the partition mechanisms between analyte, mobile phase and stationary phase. They are based on coefficients of adsorption or partition. 

Determination of solubility by headspace analysis offers several advantages over spectrophotometric techniques. First, because of the selectivity of chromatographic analysis, compound purity is not a critical factor second, absolute calibration of the gas chromatographic detector is not necessary if the response is linearly related with concentration over the range necessary for the measurements and finally, this method does not require the preparation of saturated solutions, since a partition coefficient, not a solubility, is actually measured. However, headspace methodology would probably not be applicable for determining PAH solubilities for three reasons. First, there is little data in the literature on the vapor pressures of PAHs. Second, the aqueous solubilities of most PAHs are too low to be measured by this procedure. Finally, adsorptive losses of PAHs to glass surfaces from the vapor phase would cause errors. 

---