Preparation of plates

The quantity of agar normally placed in a petri dish is 10 ml but more may be used if required. This is usually done when a long incubation period is required as plates containing only 10 ml of medium would dry out. 

The adsorbent is spread on a suitable firm support, which may be quite rigid, or flexible. Glass plates were the original support however, flexible plates have become increasingly popular. The size used depends on the type of separation to be carried out and on the type of chromatographic tank and spreading apparatus available. 

Most of the commercial apparatus is designed for plates of 20 x 5 or 20 X 20 cm, and those are now regarded as standard . It is important that the surface of the plate shall be flat, and without irregularities or blemishes. Glass plates are cleaned thoroughly before use, washed with water and a detergent, drained and dried. A final wash with acetone may be included. 

The film thickness is a most important factor in thin layer chromatography. The standard thickness is 250 pm, and there is little to be gained by departing very much from that in analytical separations (thinner layers may give rise to erratic R[ values). Thicker layers (0.5-2.0mm) are used for preparative separations, with a loading of up to 250 mg on a 20 X 20 cm plate. 

There are, in principle, four ways of applying the thin layer to its support spreading, pouring, spraying and dipping. 

2 Pouring. Many workers prefer not to use mechanical spreading methods at all. If the adsorbent is very finely divided and of homogeneous particle size, and if no binder is used, a slurry can be poured on a plate and allowed to flow over it so that it is evenly covered. Some manual dexterity is required to do this properly. Preparation of plates by pouring is particularly easy with certain types of alumina, but water alone is not usually suitable for making the slurry a volatile liquid such as ethanol (or an ethanol-water mixture) or ethyl acetate is preferable. The appropriate amounts of liquid and solid adsorbent needed to cover a plate have to be found by trial and error, and exactly those quantities should 

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ISO 9353 1991 Glass-reinforced plastics - Preparation of plates with unidirectional reinforcements by bag moulding... 

The adsorbent slurry may be applied to the TLC plates by means of several methods. For analytical work, the plates are best prepared with a special TLC adsorbent applicator which provides uniform layers and can be often adjusted to various thicknesses from 250 pm (normal) up to 500 or 1000 pm for preparative separations. The preparation of plates with a typical applicator is shown in Fig.3.1. These applicators are available from a number of suppliers of TLC equipment including most of those mentioned in Table 3.2. After the slurry has been applied, the plates are dried in air overnight or in a warm oven at 80-90°C for ca. 30 min. The dry plates are stored in a dust-free cupboard for further use. Portable cabinets for plate storage are available from a number of suppliers. 

Figure 106 takes lithography as an example and presents in diagram form the variables affecting success at the stages of pre-press, preparation of plate, choice of substrate, water quality, ink, printing proper, and variables attributable to the operator. Similar diagrams could be compiled for each of the other techniques. 

In TLC a commercial spreading device is usually used to prepare the adsorbent bed [e.g.. Refs. (2,3)]. Many laboratories have dispensed with this aspect of separation, however, since commercially prepared plates are now available for the commonly used adsorbents. The preparation of plates with an adsorbent gradient (Section 2-5F) requires special equipment [e.g.. Ref. ( )]. 

C for 30 min. Plates made with volatile organic liquids may not need this further drying. It is important to standardise this part of the preparation of plates, because the activity of the adsorbent may depend rather critically on it. 

H. Lu, H. Sun, A. Mao, H. Yang, H. Wang and X. Hu, Preparation of Plate-like Nano a-AhOj Using Nano-Aluminum Seeds by Wet Chemical Methods, Mater. Sci. Eng. A 406, 19-23 (2005). 

Preparation of plates Reversed-phase TLC plates were developed (prior to application of the dansyl amino acids), in 0.3 M sodium acetate in 40% acetonitrile and 60% water, adjusted to pH 7 with acetic acid (buffer A). After fan drying, the plates were immersed in a solution of 8 mM N,N-di-n-propyl-L-alanine and 4 mM cupric acetate in 97.5% acetonitrile and 2.5% water for 1 h and left to dry in the air. The plates are stable and can be stored for further use. 

The same general considerations apply for the site erection of spheres, with an added emphasis on accurate preparation of plates and careful fit up of plate edges prior to welding. 

The cellulose derivatives contained all three —OH groups of each glucose unit replaced by carbamate bonds. For the preparation of plates, 300 mg of each derivative (particle size 10-100 /rm) and 300 mg of cellulose microcrystalline were mixed with 3 ml water and a small amount of ethanol, as wetting agent, to obtain a suspension that was stratified on 2.6 x 7.6 cm glass microslides. Plates were dried in an oven at 105 C for 5 min to obtain layers having a thickness of about 0.25 mm [36],... 

Preparation of Plates Impregnated with Chiral Selector.. 335... 

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