Applications of Planar Chromatography

Thin-layer chromatography is now more widely used than paper chromatography. In addition to its greater resolving power, TLC is faster and plates are available with several sorbents (cellulose, alumina, silica gel). 

Partition chromatography as described in this section may be applied to two major types of problems (1) identification of unknown samples and (2) isolation of the components of a mixture. The first application is, by far, the more widely used. Paper chromatography and TLC require only a minute sample size, the analysis is fast and inexpensive, and detection is straightforward. Unknown samples are applied to a plate along with appropriate standards, and the chromatogram is developed as a single experiment. In this way any changes in experimental conditions (temperature, humidity, etc.) affect standards and unknowns to the same extent. It is then possible to compare the Rf values directly. 

Purified substances can be isolated from developed chromatograms however, only tiny amounts are present. In paper chromatography, the spot 

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Klebovich, 1., Application of planar chromatography and digital autoradiography in metabolism research, in Planar Chromatography, Nyiredy, Sz., Ed., Springer Scientific, Budapest, Hungary, 2001, pp. 293-311. 

Because of its importance, the application of planar chromatography for the analysis of various secondary metabolites in plants such as heterocyclic oxygen compounds (coumarins, flavonoids, anthocyanins, etc.) has been reviewed many times [143,144],... 

W. Cisowski, W. Dembinska-Migas, M. Krauze-Baranowska, M. Luczkiewicz, P. Migas, G. Matysik and E. Soczewinski, Application of planar chromatography to the analysis of secondary metabolites in callus cultures of different plant species. J. Plan. Chromatogr.—Mod. TLC 11 (1998)441 146. 

Sz. Nyiredy, Applicability of planar chromatography in the analysis and isolation of plant substances , in Proceedings of Biokemia XV, pp. 146-151 (1991). 

Practical Applications of Planar Chromatography-Mass Spectrometry Methodology... 

Nowadays, almost all commercially available HPLC stationary phases are also applicable to planar chromatography. In addition to the polar hydroxyl groups present on the surface of native silica, other polar functional groups attached to the silica skeleton can also enter into adsorptive interactions with suitable sample molecules (34). Silica with hydrophilic polar ligands, such as amino, cyano, and diol functions, attached to the silica skeleton by alkyl chains, all of which have been well proven in HPLC, have also been developed for TLC (34). 

For the reader interested in staying up to date with TLC, the Journal of Planar Chromatography, first published in 1988, is a good source of information. Two hooks are also suggested for the reader who wishes to study planar chromatography in greater depth. The first one discusses planar chromatography, from the basics to instrumentation and computer-aided methods [15]. The second book concentrates on TLC and describes sample preparation, sample application, phases selection, visualisation, quantitation, special techniques and combined methods such as TLC-GC, TLC-IR and TLC-MS. It also contains a useful list of suppliers for TLC instrumentation and equipment [16]. 

Additional certainty in using fj values to assign peak identity is obtained when retention times match on two columns with significantly different stationary phases, or a single planar stationary phase eluted by orthogonal, sequential application of two mobile phases. This is the principle and application of 2D chromatography discussed earlier in Section... 

A technique that can achieve the maximum attainable resolution in TLC on a given separation distance without forced flow is automated multiple development (AMD). This step-gradient technique was developed by Burger. With respect to peak capacity the technique can be compared to HPLC, but it still maintains all benefits of planar chromatography. The heart of the instrument is a specially designed vacuum-tight chamber. Following sample application... 

Volkman, J. K. and Nichols, P. D. (1991). Applications of thin layer chromatography-flame ionization detection to the analysis of lipids and pollutants in marine and environmental samples. Journal of Planar Chromatography, 4, 19-26. 

Izmailov, N.A., Shreiber, M.S. (1938) Spot chromatographic adsorption analysis and its application in pharmacy communication I. Farmatsiya, 3, 1-7 (in Russian translation into Enghsh by Berezkin, V. (1995) m. Journal of Planar Chromatography, 8,402-405). 

The earliest comprehensive descriptions of TLC-MS coupling were in three book chapters by Busch [4-6], and research papers reporting instrumentation, methodology, and applications are included in biennial reviews of planar chromatography by Sherma, the latest of which was published in 2014 [7]. 

On the basis of theory and experimental observations it can be predicted that a zone capacity of ca. 1500 could be achieved by 2-D multiple development. Because the same result can be achieved by application of 2-D forced-flow development on HPTLC plates, it can be stated that the combination of stationary phases, FFPC and "D offers a fruitful future in modem, instmmental planar chromatography. 

More stringent requirements, especially with regard to separation efficiency and reproducibihty in preparative planar chromatography also, led to increased application of precoated plates in this field. Figure 3.3 shows a scanning electron micrograph of a cross section through a PLC plate silica gel. 

Compared with liquid column chromatography, in PLC there is a certain limitation with respect to the composition of the mobile phase in the case of reversed-phase chromatography. In planar chromatography the flow of the mobile phase is normally induced by capillary forces. A prerequisite for this mechanism is that the surface of the stationary phase be wetted by the mobile phase. This, however, results in a Umitation in the maximum possible amount of water applicable in the mobile phase, is dependent on the hydrophobic character of the stationary RP phase. To... 

One of the most crucial influencing factors in planar chromatography is the vapor space and the interactions involved. The fact that the gas phase is present, in addition to stationary and mobile phases, makes planar chromatography different from other chromatographic techniques. Owing to the characteristic of an open system the stationary, mobile, and vapor phases interact with each other until they all are in equihbrium. This equilibrium is much faster obtained if chamber saturation is employed. This is the reason for differences in separation quality when saturated and unsaturated chambers are used. However, the humidity of the ambient air can also influence the activity of the layer and, thus, separation. Especially during sample application, the equihbrium between layer activity and relative humidity of the... 

Application of anticircular development to preparative planar chromatography is not popular in spite of the possibility of obtaining a good resolution of mixture components, especially of higher Rp values. Delivery of the mobile phase to the... 

Preparative planar chromatography is a very important step in the complicated procedures of isolation of group of compounds or pure substances from complex matrices. The method gives additional possibilities of using various adsorbents and eluent systems to achieve complete separation of stracmral analogs. The method also enables combining the various methods of sample application, plate development, and derivatization to achieve satisfactory separation of isolated plant extracts components. 

The latest innovation is the introduction of ultra-thin silica layers. These layers are only 10 xm thick (compared to 200-250 pm in conventional plates) and are not based on granular adsorbents but consist of monolithic silica. Ultra-thin layer chromatography (UTLC) plates offer a unique combination of short migration distances, fast development times and extremely low solvent consumption. The absence of silica particles allows UTLC silica gel layers to be manufactured without any sort of binders, that are normally needed to stabilise silica particles at the glass support surface. UTLC plates will significantly reduce analysis time, solvent consumption and increase sensitivity in both qualitative and quantitative applications (Table 4.35). Miniaturised planar chromatography will rival other microanalytical techniques. 

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