Glass supports, thin layer chromatography

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. 

Thin layer chromatography was carried out on 20x20cm glass plates coated 0.25mm thick with a suitable support and dried overnight. Silica gel G, silica gel H and cellulose were examined as the solid phases for chromatography of methanearsonate, arsenite and arsenate. Several sprays for the visualization of the arsenicals on plates were tested. Three of the more successful reagents and the colour produced with final product are shown in Table 13.2. 

There are two popular LC techniques in which the stationary bed is supported on a planar surface rather than in a column paper chromatography (PC) and thin-layer chromatography (TLC). PC preceded TLC by some 10 to 15 years, and a large number of excellent separations were devised for it. But beginning about 1956, it was found that TLC could also be used for most of these separations and that it was faster, more reproducible, more versatile, and more convenient. As a result, most laboratories have abandoned the use of PC with its large cumbersome glass chambers. Those who have not, continue to use PC because they feel that the original PC methods are superior or because of the lower cost of PC. 

Conventional thin-layer chromatography (TLC) in our experience, known under the name planar chromatography, uses horizontal or vertical glass or Teflon chambers for the development of chromatograms. As stationary phases, commonly known adsorbents or supports based on silica gel, aluminium oxide, magnesium silica, cellulose, and so forth are used particle sizes are about 20 jitm. The migration of the mobile phase is based on the phenomenon of capillary forces. This chromatographic method is described, in detail, in other sections of this volume. 

Like paper chromatography, thin-layer chromatography is a form of plane chromatography in that the stationary phase is held on a plane rather than in a column. Table 12.1 lists important stationary phases used in TLC along with the respective predominant sorption process operative with each of them. The solid phase is supported on to glass, metal or a plastic substance. (Microscope slides... 

A series of precoated plates prepared from a variety of single or mixed adsorbants on glass, plastic, aluminium, and other supports are now commonly available. These precoated plates greatly simplify the use of thin-layer chromatography. 

Thin-layer chromatography (TLC) is a planar form of chromatography useful for wide-scale qualitative analysis screening and can also be used for quantitative analysis. The stationary phase is a thin layer of finely divided adsorbent supported on a glass or aluminum plate, or plastic strip. Any of the solids used in column liquid chromatography can be used, provided a suitable binder can be found for good adherence to the plate. 

Thin-layer gel chromatography (TL GPC) is a technique utilizing the flat bed of gel supported by a plate of glass, metal or plastics. The experimental arrangement of TL GPC is similar to conventional thin-layer chromatography, but since the wet gel beds are most often used, gravitation is employed for the generation of flow instead of capillary elevation. Evidently, the procedures of over-pressurized TLC may also be applied. 

Adsorption chromatographic separation can be carried out either in closed columns or open films the latter usually consists of a rectangular film of adsorbent supported on a glass plate. Chromatography on open films is referred to as thin-layer chromatography when the adsorbent particles adhere to each other and to the plate, and as loose-layer chromatography when the adsorbent particles are nonadherent. The combination... 

Thin layer chromatography, TLC a form of planar chromatography having a coating of a solid stationary phase, e.g. silica gel or alumina, on a plate of glass or inert plastic. The liquid mobile phase moves up the plate by capillary action, reverse phase TLC plates are available where a liquid stationary phase is immobilised on the solid support. The polarity of the mobile phase is carefully chosen to obtain the best separation see elutropic series. 

Thin-layer chromatography on cellulose or silica gel (supported on paper, glass, or aluminum) ... 

Thin Layer Chromatography-.f This name (abbreviated TLC) is applied to the thin layer versions of the column techniques described in Secs. 2.6.1 to 2.6.3, other than paper chromatography. The stationary phases (except cellulose) mentioned in these sections lack the strength of paper and require the support provided by a glass plate or polyester film. 

The development of LC was rapid with the appearance of several different methods and techniques. Some trends are outlined. Liquid-liquid chromatography (LLC) was introduced in 1941. In this case, both the stationary phase and mobile phase are immiscible liquids. The stationary phase is a porous material (support) covered with a thin film of liquid. A variation of LLC is paper chromatography (PC), where the stationary phase is paper with the water included in its pores. PC was the first planar technique. The term planar comes from the fact that the stationary phase (paper) is a two-dimensional bed. A subsequent planar technique is thin-layer chromatography (TLC). In this case, the stationary phase is a thin layer of solid material, composed of small particles, spread on a glass plate or an aluminum sheet. 

Thin-layer chromatography (TLC) stationary phase is a thin layer supported on glass, plastic, or aluminum plates. 

Thin-layer chromatography (TLQ is closely related to column chromatography, in that the phases used in both techniques are essentially identical. Alumina and siHca gel are typical stationary phases, and the usual solvents are the mobile phases. There are, however, some distinct differences between TLC and column chromatography. The mobile (liquid) phase descends in column chromatography the mobile phase ascends in TLC. The column of stationary-phase material used in column chromatography is replaced by a thin layer (100 (xm) of stationary phase spread over a flat surface. A piece of window glass, a miCTOscope sUde, or a sheet of plastic can be used as the support for the thin layer of stationary phase. It is possible to prepare your own glass plates, but plastic-backed thin-layer plates are only commercially available. Plastic-backed plates are particularly attractive because they can easily be cut with scissors into strips of any size. Typical strips measure about 1X3 in., but even smaller strips can be satisfactory. 

Planar chromatographic methods include thin-layer chromatography (TLC) and paper chromatography (PC). Each makes use of a flat, relatively thin layer of material that is either self-supporting or is coated on a glass, plastic, or metal surface. The mobile phase moves through the stationary phase by capillary action, sometimes assisted by gravity or an electrical potential. 

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