Snyder classification scheme

Fig. 5 Solvent classification scheme according to Snyder (Ref. 9). (Reproduced with permission from Preston Publications.)...

The Snyder solvent classification scheme (29, 30) that has been successfully applied to LC systems (31-37) for LC separation optimization appears to be a general framework that can be used for guidance in the selection of the modifier. Some preliminary experiments have been done to determine the applicability of this approach to SFC systems as a prelude to a more in-depth, statistically-designed modifier selection study. These first experiments are the topic of this paper the basis of the proposed modifier selection scheme will now be described in detail. 

The purpose of these first experiments in the modifier survey work was to determine the applicability of the Snyder solvent classification scheme to the choice of modifier to see if an in-depth study would be warranted. The experimental conditions are described in the final section of this paper. 

Snyder, A.P. Dworzanski, J.P. Tripathi, A. Maswadeh, W.M. Wick, C.H., Correlation of mass spectrometry identified bacterial biomarkers from a fielded pyrolysis-gas chromatography-ion mobility spectrometry biodetector with the microbiological gram stain classification scheme. Ana/. Chem. 2004, 76, 6492-6499. 

However, not withstanding the above objections, further discussion of the Snyder solvent triangle classification method is justified by its common use in many solvent optimization schemes in liquid chromatography. The polarity index, P, is given by the sum of the logarithms of the polar distribution constants for ethanol, dioxane and nltromethane and the selectivity parameters, X, as the ratio of the polar distribution constant for solute i to... 

The main strength of the Snyder scheme is for the classification of solvent selectivity. We have seen from table 2.8 that solvents that are chemically similar yield similar selectivity parameters. This type of classification can be made on the basis of structural information alone. However, the Snyder scheme goes one step further, in that it classifies different chemical classes into a single selectivity group. From the definition equations (2.14 through 2.17) we see that the three selectivity parameters are correlated by the equation... 

The Snyder scheme may best be used to classify the many solvents that may potentially be used in chromatography into a limited number of categories. This classification may then be used to aid in the selection of solvents which show different selectivity. 

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