Further Reading

Gazdag M, Szepesi G, Hernyes M and Vegh Z (1984) Optimisation of reversed-phase ion-pair chromatography by overpressurized thin-layer chromatography 1. Overpressure thin-layer chromatography. Journal of Chromatography 290: 127-134.

Jost W and Hauk HE (1983) Reversed-phase thin-layer chromatography of nitrogen bases using alkyl sulphon-ates as ion-pair reagents. Journal of Chromatography 264: 91-98.

Kovacs-Hadady K (1996) A systematic study of the adsorption of different ion-pairing reagents on reversed-phase layers. Journal of Planar Chromatography 9: 174-177.

Lepri L, Desideri PG and Heimler D (1978) Soap thin-layer chromatography of some primary aliphatic amines. Journal of Chromatography 153: 77-82.

Ruane RJ, Wilson ID and Troke JA (1986) Normal- and reversed-phase ion-pair thin-layer chromatography with bifunctional (bolaform) bis(trimethylammonium) ion-pair reagents. Journal of Chromatography 368: 168-173.

F. Rabel, EM Science, Gibbstown, NJ, USA Copyright © 2000 Academic Press

Although many new tools, such as high performance liquid chromatography (HPLC) and capillary zone electrophoresis, have been developed for the analytical laboratory, none can be used as quickly or inexpensively as planar or thin-layer chromatography (TLC). This tool can be used as a complete analytical system (from initial separation to final quantitation) or as a stepping stone or aid for other analytical methods. It is one of the few analytical tools that requires no sample clean-up, saving time and money. Many samples can be applied and analysed at the same time on a single TLC plate. With the combinatorial chemistries now being used to develop new drugs, renewed interest in this high throughput tool has become apparent.

One distinct advantage, often overlooked, is that when using TLC for any screening or method development, it shows components at the origin that do not move and will over time contaminate other analytical systems, such as an HPLC column. This potential problem would not be apparent if optimizing solely on the HPLC system. Likewise, samples applied after sample preparation would show whether or not sufficient clean-up was actually accomplished with the sample preparation technique used. This can save countless hours of frustration that would develop long after the initial method was thought to be sufficient for the analytical results needed.

Planar chromatography is also useful when optimizing a solid-phase extraction (SPE) method, when

Szepesi G, Gazdag M, Pap-Sziklay ZS and Vegh Z (1984) Optimisation of reversed-phase ion-pair chromatogra-phy by over-pressurized thin-layer chromatography. III. Over-pressurized thin-layer chromatography using 10-camphor sulphonic acid as ion-pair reagent. Chromatographia 19: 422-430.

Tivert A-M and Backman A (1989) Journal of Planar Chromatography 2: 472-473.

Tomkinson G, Wilson ID and Ruane RJ (1989) Reversephase ion-pair high performance thin-layer chromato-graphy of acids on a C-2 bonded silica gel. Journal of Planar Chromatography 2: 224-227.

Wilson ID (1986) Ion-pair reversed-phase thin-layer chromatography of organic acids. Re-investigation of the effects of solvent pH on RF values. Journal of Chromatography 354: 99-106.

many SPE tubes and extracting solvents will be tried. Up to 20 samples can be spotted on each side of a 20 x 20 cm TLC plate (Figure 1). Each side can be developed in 10-20 min to just 6-8 cm. A quick look under UV light or spray visualization can show the presence or absence of a compound of interest. This is certainly many times faster than doing the 40 samples on an HPLC system, one at time.

Samples from any fast TLC screening which are found to be positive for the component of interest can be confirmed or further quantified with TLC by applying standards and using densitometry or can be transferred to another analytical technique.

This is a brief review of the layers most often used and referenced in planar chromatography. For details on less used layers or more information on those discussed, the reader is referred to the Stahl book listed in the Further Reading section. A few recommended methods or tips are included within each section, where their use will improve performance or the property of a plate or separation.

Figure 1 Multi-spotted 20 x 20 cm TLC plate.

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