chapter  2
24 Pages

Chapter Principles of Chiral Separations by Free-Solution Electrophoresis

Separation selectivity is a prerequisite to a successful chemical analysis. Therefore, the attainment of reasonable separation selectivity is its necessary starting step. The difference between the migration speeds of analytes toward their solvent is the very cause for the separation selectivity in electrophoretic methods. Difference in chargeto-volume ratio of analytes is the principle feature that causes different migration speeds of the analytes in their solvent. The shape and solvation layer of the charged species are additional characteristics affecting the speed [1,2]. The layer of solvent molecules rmly adheres to the dissolved species and migrates with it. In this way, the layer increases the volume of the migrating dissolved species and masks their shape difference. Hence, crystallographic radii of ions and molecules underestimate their migration volumes. Water is a standard electrophoretic solvent. Different hydrophilicity of either analyzed species or their large building blocks gives therefore the chance to affect the mobility of the dissolved species by means of the composition

of the background electrolyte (BGE) solvent [2,3]. The macroscopic liquid ow is a secondary process that frequently occurs in electrophoretic separation capillaries. This ow does not affect the difference between the migration speeds of analytes toward their solvent, disregarding the origin of the ow; however, it must be taken into account in the calculation of separation selectivity due to its effect on the overall migration velocity of the zones of analytes [1-3].