Plastic supports, thin layer chromatography

In paper chromatography we use filter paper, marketed for this purpose. It comes usually in the form of a 2-5 cm-wide tape, from which a strip of the necessary length can easily be cut. The more modern technique of thin layer chromatography (TLC), makes use of thin sheets of aluminium oxide, silica-gel, cellulose or some other material, supported by a metal sheet or a polymer. Chromatographic thin layers can be prepared in the laboratory from commercially available adsorbents. A thick suspension of these is made with water (usually a 2 1 w/w mixture of water adsorbent is made up) and this is then spread on a metal plate with a suitable spreader device. Techniques vary from device to device, and the instructions of the manufacturer should be followed whenever thin layer plates are to be prepared. Ready-made thin layer sheets are also available commercially. These contain the active material spread on a plastic support. Thin-layer chromatographic materials, especially ready-made plates, are much more expensive than chromatographic paper, but normally offer faster and sharper separations than the paper. The procedures described in Section VI.20 can be carried out both on a slow chromatographic paper (e.g. Whatman No. 1) or on a cellulose thin layer (e.g. Whatman cellulose). 

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. 

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 (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. 

Particularly in the beginning of thin-layer chromatography, but also today, sorbents without chemically modified surfaces are of most importance. In former times hand-made thin-layer plates were used nearly exclusively, but today the trend has moved in the direction of industrial precoated layers. In addition to glass plates, plastic and aluminium sheets are also offered as supports for the precoated layers. To stabilize the precoated layers mechanically, special binders are added that do not or nearly do not interfere with the chromatographic properties. To enlarge the possibilities of detection, added indicators can be mixed homogeneously with sorbents. Different types of silica gel are by far the most versatile and therefore the most frequently used stationary phases in the case of bulk sorbents as well as for application to precoated layers. 

TLC is carried out on a thin layer of adsorbent on a glass or plastic support (other supports have been used). It has sometimes been referred to as planer chromatography since the separation occurs in a plane. Paper chromatography, which is carried out using a piece of paper, usually filter paper, is very similar to TLC and will not be covered here. 

The support medium may be a sheet of cellulose or a glass or plastic plate covered with a thin coating of silica gel, alumina, or cellulose. Large sheets of cellulose chromatography paper are available in different porosities. These may be cut to the appropriate size and used without further treatment. The paper should never be handled with bare fingers. Although thin-layer plates can easily be prepared, it is much more convenient to purchase ready-made plates. These are available in a variety of sizes, materials, and thicknesses of stationary support. They are relatively inexpensive and have a more uniform support thickness than hand-made plates. 

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