Drying before development

Figure 41. Influence of adequate drying before developing...

Samples are usually applied as round spots. However, application in a thin line or band is best when especially high resolution is required. The starting spot or line must be as narrow as possible to obtain sharply separated zones. Wide initial zones can be concentrated by holding the paper in a trough of polar solvent such as acetone or methanol and allowing the front to travel up to the starting line. The paper then must be dried before development, which is carried out by placing the paper so that a few millimeters dip into the mobile phase but the dried sample does not. 

The influence of sedimentation process on the value of reduced thickness of various dry powder developers is carried out in our experiments. Fig 1 illustrates the pictures of real developer s layers before (a, c) and after (b, d) penetrant application. The pictures were... 

All glassware should be scrupulously clean and, for most purposes, dry before being employed in preparative work in the laboratory. It is well to develop the habit of cleaning all glass apparatus immediately after use the nature of the dirt will, in general, be known at the time, and, furthermore, the cleaning process becomes more difficult if the dirty apparatus is allowed to stand for any considerable period, particularly if volatile solvents have evaporated in the meantime. 

Repeated chromatography of the sample in the same direction with the chromatographic plate being dried before all re-developments. 

At every stage of the development process, the results of a reaction or process stage will be analysed in one of two ways. The reaction mixture itself will be sampled and analysed to yield information such as extent/completion of reaction, reaction yield or reaction purity. Alternatively, the reaction product will be isolated and dried before sampling and analysis. Typical analytical information in this case would include both chemical and physical characterisation, plus quantitative data to ensure conformance with some pre-defined specification or to provide batch data on which a suitable specification will ultimately be based. Note that however quickly the analytical data are provided, there is a disconnect from the reaction, which means that reaction control is impossible and that... 

To Fix and Finish tie Picture.—When the plate has been well washed after the development, by pouring water over it from a jug, the yellow iodide of silver should ho dissolved out by means of either a saturated solution of hyposulphite of soda, or a solution of cyanide of potassium—strength about five grains to the ounce of water. This should be poured over the plate, and should be allowed to run backwards and forwards over it until the whole of the yellow iodide of silver in the plato has disappeared aftor which it should bo thoroughly well washed, by pouring water over it from a jug, and sot up to drain and dry or it may be dried before a fire. It is then ready to bo varnished,... 

Dry-column flash chromatography. This technique has been developed from flash chromatography by L. M. Harwood.64 The principal feature is that suction is applied to the column packing, and eluting solvents are added in predetermined volumes with the column being allowed to run dry before the next fraction is added. Furthermore the apparatus is both simple and of easy operation. 

Prints to be toned should be darker and softer than normal prints. Use approximately 25% overexposure on the next softer grade of paper. Development of the print should be carried out in a standard developer, such as Kodak D-72, with particular attention given to avoid underdevelopment or forcing the print with overdevelopment. Prints should be fixed as usual, thoroughly washed, and completely dried before toning. 

Procedure Spot 0.1 mL of the Sample Solution in a line across a 20- x 20-cm glass plate coated with a 0.25-mm layer of Silica Gel G, approximately 3 cm from the bottom edge. Allow the plate to dry for about 20 min in the dark, then develop with the Solvent System in an unlined tank equilibrated for at least 20 min before the plate is inserted. Allow the solvent front to reach within about 3 cm of the top of the plate. Dry the developed plate in the dark. 

In TLC, the silica or alumina layer is dry before it is used and contacts the solvent only after it has been placed into the developing chamber. This is why, in DCC, the dry column is charged with the sample. Contrary to the normal CC, DCC is a nonelution tech-... 

B.S. Green and co-workers developed an improved preparation of the clathrate host compound tri-o-thymotide (TOT) and other trisalicylide derivatives. The synthesis began with the preparation of orfho-thymotic acid from thymol using the Kolbe-Schmitt reaction. The authors found that the yield of the product was dramatically increased when the reactants, solvents, and reagents were dried before use. Thus, thymol was dissolved in dry xylene, sodium metal was added and the temperature was kept at 130 °C for 20h in a dry carbon dioxide atmosphere. The desired carboxylated product was isolated in good yield. Finally, cyclodehydration with POCI3 afforded TOT in almost quantitative yield. 

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