Gradient thin layer chromatography (GTLC) defined as a chromatographic technique using within the separation area locally different separation conditions can be applied for manifold purposes, e.g. for simultaneous chromatography of substances differing in polarity very much (for screening tests), for lowering of the detection limit by sharpening of the chromatographic zones, for stationary equilibrium chromatography, for speeding up the search for better chromatographic conditions.
A systematic nomenclature of the arrangement of a gradient is proposed related to the direction of solvent flow. One has to discriminate between arrangements tending to increase the substance diffusion in direction of solvent flow (not very useful) and arrangements which counteract diffusion or which remain neutral in this respect. Gradients in the stationary phase, also for two-dimensional technique, are described in more details in this paper. A continuous gradient arranged (“anti”-) diagonal to flow direction is described here to the first time.
In a continuation of this paper gradients in the mobile phase will be described, including examples of application and new developments, e.g. a solvent flux gradient (Fließmitteldurchsatz-Gradient) leading to a stationary chromatographic equilibrium.