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Partition between two immiscible solvents is widely used in sample preparation procedures for matrix simplification and isolation of target analytes, for separations using countercurrent, centrifugal partition, and liquid-liquid chromatography, and as a method for determining descriptors for use in modeling chemical, biological, and environmental processes. Until recently, most applications employed water as one component of the biphasic system. For compounds of low water solubility or stability, a series of totally organic biphasic systems have been developed to enhance the application range of liquid-liquid partition methods. These systems, their characterization using the solvation parameter model, and applications to sample preparation and the determination of descriptors are described in this review., (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A combination of gas chromatography and liquid-liquid partitions in totally organic biphasic systems is used to determine descriptor values for compounds of low volatility suitable for characterizing open tubular columns at high temperatures. The descriptor database of varied compounds includes several difficult to determine by conventional techniques due to their low water solubility or stability. The descriptor database facilitates an expansion of the descriptor space and compound variation for characterizing separation systems. As an application the descriptor database is used to determine the system constants for SPB-Octyl, HP-5, Rxi-5Sil MS, Rtx-440, and Rtx-OPP for the temperature range 200-300°C. As an example of the broader affect of temperature on column selectivity the variation of the system constants for Rtx-440 over the temperature range 60-300°C is described in detail. These studies demonstrate the persistence of polar interactions to the highest temperature studied and that at high temperatures selectivity differences persist for moderately polar stationary phases., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Retention factors on a minimum of eight stationary phases at various temperatures by gas-liquid chromatography and liquid-liquid partition coefficients for five totally organic biphasic systems were combined to estimate descriptors for 28 fragrance compounds with an emphasis on compounds that are known or potential allergens. The descriptors facilitated the estimation of several properties of biological and environmental interest (sensory irritation threshold, odor detection threshold, nasal pungency threshold, skin permeability from water, skin-water partition coefficients, octanol-water partition coefficients, absorption by air particles, adsorption by diesel soot particles, air-water partition coefficients, and adsorption by film water). The descriptors are suitable for use in the solvation parameter model and facilitate the estimation of a wide range of physicochemical, chromatographic, biological, and environmental properties using existing models., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Partition coefficients for varied compounds were determined for the organic solvent-dimethyl sulfoxide biphasic partition system where the organic solvent is n-heptane or isopentyl ether. These partition coefficient databases are analyzed using the solvation parameter model facilitating a quantitative comparison of the dimethyl sulfoxide-based partition systems with other totally organic partition systems. Dimethyl sulfoxide is a moderately cohesive solvent, reasonably dipolar/polarizable and strongly hydrogen-bond basic. Although generally considered to be non-hydrogen-bond acidic, analysis of the partition coefficient database strongly supports reclassification as a weak hydrogen-bond acid in agreement with recent literature. The system constants for the n-heptane-dimethyl sulfoxide biphasic system provide an explanation of the mechanism for the selective isolation of polycyclic aromatic compounds from mixtures containing low-polarity hydrocarbons based on the capability of the polar interactions (dipolarity/polarizability and hydrogen-bonding) to overcome the opposing cohesive forces in dimethyl sulfoxide that are absent for the interactions with hydrocarbons of low polarity. In addition, dimethyl sulfoxide-organic solvent systems afford a complementary approach to other totally organic biphasic partition systems for descriptor measurements of compounds virtually insoluble in water., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Partition coefficients for varied compounds were determined for the organic solvent-propylene carbonate biphasic partition system where the organic solvent is n-heptane, isopentyl ether or 1-octanol. These partition coefficient databases are analyzed using the solvation parameter model facilitating a quantitative comparison of the propylene carbonate-based partition systems with other totally organic partition systems. Propylene carbonate is a weak to intermediate cohesive solvent, reasonably dipolar/polarizable and hydrogen-bond basic, and weak hydrogen-bond acidic. Propylene carbonate-organic solvent systems offer a complementary approach to other totally organic biphasic partition systems for sample preparation and descriptor measurements of compounds virtually insoluble or unstable in water., (© 2010 Elsevier B.V. All rights reserved.)

Partition coefficients for varied compounds were determined for the organic solvent-formamide biphasic partition system where the organic solvent is 1,2-dichloroethane, 1-octanol or isopentyl ether. These partition coefficient databases are analyzed using the solvation parameter model facilitating a quantitative comparison of the formamide-based partition systems with other totally organic and water-based partition systems. Formamide is shown to be a less cohesive and hydrogen-bond acidic solvent than water with similar hydrogen-bond basicity and dipolarity/polarizability. Compared with other organic solvents its higher cohesion, dipolarity/polarizability and hydrogen-bonding capability make it a useful base solvent for forming biphasic partition systems with a range of system properties obtained through variation of the counter solvent. Formamide-organic solvent systems offer a complementary approach to water-based partition systems for sample preparation and the determination of descriptors for compounds virtually insoluble in water or unstable in water., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Partition coefficients for 84 varied compounds were determined for n-heptane-formamide biphasic partition system and used to derive a model for the distribution of neutral compounds between the n-heptane-rich and formamide-rich layers. The partition coefficients, log K(p), were correlated through the solvation parameter model giving log K(p)=0.083+0.559E-2.244S-3.250A-1.614B+2.387V with a multiple correlation coefficient of 0.996, standard error of the estimate 0.139, and Fisher statistic 1791. In the model, the solute descriptors are excess molar refraction, E, dipolarity/polarizability, S, overall hydrogen-bond acidity, A, overall hydrogen-bond basicity, B, and McGowan's characteristic volume, V. The model is expected to be able to estimate further values of the partition coefficient to about 0.13 log units for the same descriptor space covered by the calibration compounds (E=-0.26-2.29, S=0-1.93, A=0-1.25, B=0.02-1.58, and V=0.78-2.50). The n-heptane-formamide partition system is shown to have different selectivity to other totally organic biphasic systems and to be suitable for estimating descriptor values for compounds of low water solubility and/or stability.