Thin-layer sorbents

Theoretically any metal oxide could be used as a thin-layer sorbent, but most have no specific properties that promote a unique separation or selectivity to a thin-layer plate. Infrequently, someone publishes work done on another metal oxide, but only those mentioned above are used frequently and are considered significant. 

H. E. Hauck and W. lost, Sorbent materials and precoated layers in thin-layer cltromatography , Chromatogr. Sci. 47 251-330 (1990). 

Electromagnetic radiation energy can be used to stimulate substances to fluorescence after separation by thin-layer chromatography. Its action makes it possible to convert some nonfluorescent substances into fluorescent derivatives. The active sorbents often act as catalysts in such processes (cf. Chapter 1.1). 

Modem planar chromatography is suitable not only for qualitative and quantitative analysis but also for preparative purposes. The separation efficiency of a thin-layer chromatographic system is independent of this intended purpose and is mainly determined by the quahty of the stationary phase, that is to say, by the applied coated layer. Therefore, progress in modem planar chromatography can be attributed not only to the development of the efficiency of the instmments but also to a large extent to the availability of high-quahty precoated layers. And today, as in the past, bulk sorbents for self production, especially of preparative layer chromatography (PLC) layers, are widely used. 

A special feature of aluminum oxides is the fact that these sorbents are adjusted to different pH values for thin-layer chromatographic purposes. The acidic aluminas are in the pH range of 4.0 to 4.5, whereas neutral signifies a pH range between 7.0 and 8.0, and basic aluminas have a pH value of approximately 9.0 to 10.0. 

There are several types of sorbent materials in the market today, other than commonly used silica and alumina. Some of these sorbents are chemically modihed to a certain extent to improve the properties of the thin layer for a wide variety of compounds, as well as for better resolution. 

Rebal, F.M., Sorbents and precoated layers in thin-layer chromatography, in Handbook of Thin Layer Chromatography, 3rd ed., Vol. 89, Sherma, J. and Fried, B., Eds., Marcel Dekker, New York, 2003, pp. 99-133. 

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). 

Activated carbon, which is a common trapping sorbent for organic species, can also be used for trace metals.1 This material is typically used by passing the samples through a thin layer (50 to 150 mg) of the activated carbon that is supported on a filter disk. It can also be used by shaking 50 to 150 mg of activated carbon in the solution containing the heavy metal, and then filtering the sorbent out of the solution. 

Nonporous polyethylene or silicone materials Silicone rods or bars coated with silicone Glass fibers coated with a thin layer of various sorbent materials... 

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