TLC Developing Chambers

Solvent systems in whose phase diagram there is in any danger of a miscibility gap are also critical. Even with small changes in temperature, these can lead to emulsion formation, i.e. separation of the mixture (example the DAB solvent system for the sugars fructose, glucose, lactose and sucrose). 

In the early days of TLC, before the advent of HPLC, researchers experimented in their laboratories with developing chambers of glass, sometimes V4A steel or, for less aggressive solvent systems, plastics. Various chambers were used for the following purposes  

After some years, two of these development methods are still used, but new techniques of performing them have come along (see Chapter 11 Special Methods in TLC ). Ascending development is referred to in the present book as the classical method, as in the author s opinion it offers a wider spectrum of possibilities than horizontal development. Lively discussions continue in TLC expert circles on the subject of which of these two methods of development is the better . But what does better mean Every user must find this out for himself or herself at his or her workplace, often doing this afresh for each task. 

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If they are used correctly, all the TLC developing chambers described after this point in the book fulfill the requirements for identity testing, purity determinations and assays. 

All the equipment is extremely expensive (see also Section 4.2 TLC Developing Chambers ). 

Place the plate in a TLC developing chamber, making sure that the developer level stays below the hne along which samples are spotted. The developer is 1 A/ LiCl2 in 1 M acetic acid. 

Prepare five micropipettes to spot the plate. The preparation of these pipettes is described and illustrated in Technique 20, Section 20.4. Prepare a TLC development chamber with methylene chloride (see Technique 20, Section 20.5). A beaker covered with aluminum foil or a wide-mouth, screw-cap bottle is a suitable container to use (see Technique 20, Figure 20.4). The backing on the TLC plates is thin, so if it touches the filter paper liner of the development chamber at any point, solvent will begin to diffuse onto the absorbent surface at that point. To avoid this, be sure that the filter paper liner does not go completely around the inside of the container. A space about 2.5 inches wide must be provided. Note This development chamber will also be used for Experiments 6C and 6D.)... 

Your instructor will assign you a pair of compounds to run on TLC, or you will select your own pair. You will need to obtain about 05 mL of three solutions one solution of each of the two individual compoimds and a solution containing both compoimds. Prepare three thin-layer plates in the same way as you did in Experiment 5A, except that each plate should be 10 cm X 3.3 cm. When you mark them with a pencil for spotting, make three marks 1 cm apart. Prepare three micropipettes to spot the plates. Prepare three TLC development chambers as you did in Experiment 5A, with each chamber containing one of the three solvents suggested for your pair of compounds. 

Before running the column, assemble the following glassware and liquids. Obtain four dry test tubes (16 x 100 mm) and number them 1 through 4.Prepare two dry Pasteur pipettes with bulbs attached. Place 9.0 mL of hexane, 2.0 mL of acetone, and 2.0 mL of a solution of 70% hexane-30% acetone (by volume) into three Erlenmeyer flasks. Clearly label and stopper each flask. Place 0.3 mL of a solution containing fluorene and fluorenone into a small test tube. Stopper the test tube. Prepare one 10 cm x 3.3 cm TLC plate with four marks for spotting. Use the same TLC development chamber with methylene chloride that you used in Part A. Prepare four micropipettes to spot the plates. 

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