Solute–Liquid Interaction in Gas Chromatography

Abstract

Solute separation in GC results from the difference in their migration velocities in a column. That difference, in turn, is a result of the difference in the solute interaction with the columns stationary phase. The stronger is the interaction, the lower is the migration velocity. Depending on the stationary phase typesolid or liquida solute can be adsorbed on the solid surface, or it can be absorbed by the liquid (dissolved in it). This chapter focuses on the GC-related parameters of interaction of solutes with liquid stationary phases. Distribution Constant and Retention FactorConsider a layer of a liquid (the liquid phase) and a layer of an inert gas (the gas phase) that are in contact with each other, Figure 5.1. In this chapter, the layers represent organic liquid polymer film and a carrier gas in a capillary (open tubular) column, respectively, Figure 2.1a. Suppose that a solute was added to the gas, and the entire three-component system was sealed. A fraction of the solute added to the gas can be absorbed by the liquid (dissolved in it). Of the primary concern for this chapter is a chromatographically meaningful description of equilibrium of a solute solvationevaporation (solvation in the liquid and evaporation into the gas) or, in broader terms, equilibrium of a solute-liquid interaction. The equilibrium takes place at a certain distribution of a solute between the gas and the liquid. The gas is inert and has no effect on the equilibrium distribution of a solute between the two phases. This means that replacement of one gas with another has no effect on the equilibrium.The equilibrium distribution of a solute between a gas and a liquid, Figure 5.1, can be described by the distribution constant [1] (partition coefficient [2-8]), K c , defined as [2][3][4][5][6][7]9] K c ¼ C sol;f C sol;g ð5:1Þwhere C sol,g and C sol,f are concentrations (mass per volume, mole per volume, and so forth) of the solute in a liquid film and a gas, respectively.Temperature-Programmed Gas Chromatography. Leonid M. Blumberg