ABSTRACT
In liquid chromatography (LC), the mobile phase is a liquid. The corresponding stationary phases consist predominantly of solid surfaces. These surfaces can be the original support materials themselves, or they may consist of various chemical structures attached to the support materials. (Such modifications are discussed in detail later.) This type of chromatography is addressed as liquid-solid chromatography (LSC). [In the physicochemical treatment, the total stationary phase, beyond the surface of the adsorbent, is considered to also include the first adsorbed layers of the mobile phase.]
In a different type of chromatography, which nowadays is used only in very few practical applications of classic chromatography [1,2], the stationary phase is also a liquid, which is adsorbed as a bulky film onto a solid support. Stationary liquid-phase and mobile liquidphase are immiscible; their equilibrium composition is interrelated by the tie-lines (connodes) of the miscibility gap. Mobile and stationary phases employed are usually at least ternary mixtures, occasionally including polymeric components [1]. This type of chromatography is addressed as liquid-liquid chromatography (LLC). In "ideal" LLC the influence of the surface on the partition equilibrium is negligible. Partition between two liquid phases is also the basis of countercurrent chromatography [3]. In this technique, the liquid stationary phase is not adsorbed onto any support material, but the liquid mobile phase moves through the stationary liquid (e.g., in the form of upstreaming liquid bubbles or by motion in a helical coil). All commonly used experimental techniques use density differences between the two liquid phases as driving forces for phase movement.
