Solvent liquid, Snyder characterization

The solvent triangle classification method of Snyder Is the most cosDBon approach to solvent characterization used by chromatographers (510,517). The solvent polarity index, P, and solvent selectivity factors, X), which characterize the relative importemce of orientation and proton donor/acceptor interactions to the total polarity, were based on Rohrscbneider s compilation of experimental gas-liquid distribution constants for a number of test solutes in 75 common, volatile solvents. Snyder chose the solutes nitromethane, ethanol and dloxane as probes for a solvent s capacity for orientation, proton acceptor and proton donor capacity, respectively. The influence of solute molecular size, solute/solvent dispersion interactions, and solute/solvent induction interactions as a result of solvent polarizability were subtracted from the experimental distribution constants first multiplying the experimental distribution constant by the solvent molar volume and thm referencing this quantity to the value calculated for a hypothetical n-alkane with a molar volume identical to the test solute. Each value was then corrected empirically to give a value of zero for the polar distribution constant of the test solutes for saturated hydrocarbon solvents. These residual, values were supposed to arise from inductive and... 

Besides substance lipophilicity, the polarity of the organic solvent also determines extraction efficiency premising sufficient solubility. Polarity of liquids can be characterized by the Snyder polarity index (P ) sorting solvents from smallest polarity (pentane, P O), over small (methyl-ferf-butyl ether, MTBE, P 2.5 diethylether, Et20 P 2.8 dichloromethane P 3.1), and medium (chloroform P 4.1 ethylacetate, EE P 4.4) to high polarity (dimethylsulfoxide, DMSO P 7.2 water P 10.2) [91]. 

Snyder has discussed liquid solvent characterization on several occasions (29,30,38,39). One of the very interesting points is that when several solvents have essentially the same solvent power as described by the Hildebrand solubility parameter (40), those solvents often do not dissolve a particular solute to the same extent. This is attributed to the fact that the Hildebrand solubility parameter does not, and cannot by regular solution theory. 

The literature of QSRR with LSS is dominated by a specific SSD, the I ER solute parameters V, E, S, A, and B, as defined in Equation 15.2. An extraordinary amount of attention has been paid to predict retention (24,25) and to establish phase selectivity in MEKC using LSER (5, 7, 26-31). Attempts to classify and to contrast micellar phases with basis on the LSER coefficients have been pursued by many researchers (5,26,27,29). Interesting approaches comprise the classification of micellar phases by the combined use of LSER parameters and retention indexes (32), the clustering of micellar systems by principal component analysis (26), the use of LSER parameters to compose vectors for characterization of lipophilicity scales (33), and, more recently, the establishment of micellar selectivity triangles (34,35) in analogy to the solvent selectivity triangle introduced by Snyder to classify solvents and ultimately mobile phases in liquid chromatography. 

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