Two-dimensional planar chromatography

Two-dimensional planar chromatography (2D-TLC) is frequently used in combination with autoradiography or digital autoradiography (DAR) in studies on metabolism. Examples of 2D-TLC-DAR will be given in the analysis of pharmaceutical products. Other applications generally use either different types of development, or utilise different interactions for separation, or different stationary phases, such as elution-displacement absorption-partition normal phase-reversed phase ion exchange-normal phase. 

Two-Dimensional Planar Chromatography and Coupled-Column Chromatography... 

Many examples of planar systems used for two-dimensional liquid chromatography (2DLC) abound in the literature. In the quest for higher performance... 

Two-dimensional planar electrophoresis was first used in 1951 (8), while electrophoresis was coupled with thin-layer chromatography (TLC) in 1964 to separate mixtures of nucleosides and nucleotides (9). These techniques were novel and led to other great discoveries, but did not survive the test of time, and they are no longer commonly used. TLC-electrophoresis in particular was an awkward technique to... 

Two-dimensional separations can be represented on a flat bed, by analogy with planar chromatography, with components represented by a series of dots . In fact, zone broadening processes in the two dimensions result in elliptically shaped spots centred on each dot . Overlap of the spots is then possible, but Bertsch (30) also showed how the contributors to the overall resolution, R, along the two axes, and Ry contribute to the final resolution according to the following ... 

Two-dimensional separations in planar chromatography are rather trivial to perform. All unidimensional multiple development techniques employ successive repeated development of the layer in the same direction, with removal of the mobile phase between developments. The main variants are multiple chromatography and incremental multiple development. The basis for automated multiple development (AMD) is the automation of unidimensional, incremental, multiple development with a reverse solvent strength gradient [998]. 2D TLC finds limited use, and is mainly a qualitative technique. 

This effect is illustrated in Fig. 17.1. Multidimensional chromatography separations can be done in planar systems or coupled-column systems. Examples of planar systems include two-dimensional thin-layer chromatography (TLC) (Consden et al., 1944 Grinberg et al., 1990), where successive one-dimensional TLC experiments are performed at 90° angles with different solvents, and 2D electrophoresis, where gel electrophoresis is run in the first dimension followed by isoelectric focusing in the second dimension (O Farrell, 1975 Anderson et al., 1981 Celis and... 

In the following discussion, two-dimensional and multidimensional planar chromatography are defined, the above-mentioned possibilities are discussed in detail, and attention is drawn to the different possibilities, as well as the advantages and limitations of the various modes of multidimensional planar chromatography. 

In planar chromatography, the fractions are not always transferred to another separation system, but rather a secondary separation is developed, orthogonally on the same chromatographic plate. Therefore, for all substances not completely separated it is possible that baseline separation can be achieved by means of a second separation process with an appropriate mobile (stationary) phase. Figure 8.2 shows that in the second dimension a theoretically unlimited number of secondary columns can be applied. Because of this, the terminology two-dimensional PC is not sufficiently... 

D. S. Risley, R. Kleyle, S. Flabibi-Goudarzi and D. Nurok, Correlations between the ranking of one- and two-dimensional solvent systems for planar chromatography , J. Planar Chromatogr. 3 216-221 (1990). 

Consden et al. 14 published the two-dimensional development of a planar (paper) chromatogram. Later on. the method was widely used to improve a wide range of planar separation methods. Using the same stationary and mobile phase, the spot capacity has been multiplied with a factor of 1.44 (the square root of 2) (18-2(). Two-dimensional chromatography can be performed by using the same or different stationary and mobile phases. By changing the mobile phase composition the mode of development... 

In the two decades after its introduction, TLC advanced in a number of fields. One of these was the improvement in multidimensional planar chromatography where a different chromatographic or electrophoretic technique in the second dimension follows the first dimensional chromatography. 

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