Solvents Snyder’s classification

The PRISMA model developed by Nyiredy and co-workers (Nyiredy et al., 1985 Dallenbach-Tolke et al., 1986 Nyiredy and Fater, 1995 Nyiredy, 2002) for use in Over Pressured Layer Chromatography is a three-dimensional model that correlates solvent strength and the selectivity of different mobile phases. Silica gel is used as the stationary phase and solvent selection is performed according to Snyder s solvent classification (Tab. 4.7). 

Nyiredy et al. have developed an optimization model called PRISMA for the optimization of the mobile phase for OPLC (59). PRISMA is a three-dimensional model that correlates the solvent strength and the proportion of eluent constituents, which determine the selectivity of mobile phases applying Snyder s solvent classification (60). 

Seleetion of basic parameters of chromatographic process (stationary phase, proper pure solvents according to Snyder s classification, and vapor phase)... 

Snyder s classification of solvent properties is important in the selection of the chromatographic conditions and the optimization of the chromatographic processes. 

To maximize the differences in selectivity, solvents must be selected from different selectivity groups that are situated close to the Snyder s triangle apexes. For example, for NPTLC, a suitable selection could be solvents from several groups of Snyder s classifications (I, VII, and VIII), mixed with hexane to control solvent strength. 

The solvent triangle classification method of Snyder is the most enduring approach to solvent characterization used by chromatographers, but in several respects is not entirely satisfactory [568,575,576]. Snyder classified solvents based on their interactions with three prototypical solutes determined by their gas-liquid distribution constants corrected for differences in solvent size, polarizability and dispersion interactions (assumed identical to the interactions of a hypothetical n-alkane with the same molar volume). Each value was then corrected empirically to give a value of zero for the polar distribution constant for saturated hydrocarbon solvents. Snyder chose the solutes nitromethane, ethanol and dioxane as probes for a solvent s capacity for dipole-type, hydrogen-bond base and hydrogen-bond acid interactions, respectively. The sum of the three polar distribution constants provides a measure of the solvent strength P ) and the ratio of the individual polar distribution constants to their sum a measure of selectivity (xn, and Xd). 

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. 

---