Quick Modification of a TLC Plate by Use of a Disposable Dipping Chamber Occasionally, one must modify a thin-layer chromatographic plate by dipping it into a solution of an appropriate reagent. Typically, a beaker or an expensive dipping chamber is used, but both of these containers usually require the preparation of a large excess of reagent solution. If this solution involves a rare or costly reagent, the procedure can he very wasteful. A very simple alternative to the usual containers is an inexpensive disposable polyethylene bag. By choosing the appropriate dimensions to match the TLC plate, dipping may be achieved with very little reagent solution. For example, a 5 X 20-cm Silica Gel G plate was treated with 10%silver nitrate in 50% aqueous ethanol with the aid of a 10 X 15-cm bag of 0.1 mm thickness. Ten milliliters ofthe reagent solution sufficed. The bag was charged with the solution and held against a flat vertical surface. The plate was inserted, and the solution then was forced uo and over the d a t e once bv. eentlv - . compressing the bag with a blank glass plate. The wet plate was quickly removed from the bag, then prepared for spotting and development by drying and activating a t 120' C. Later use of the treated plates to separate a cisltrans mixture showed the nlates to he hiehlv " < effective and uniform. Polyethylene is inert to most solvents and contains no potentially leachable plasticizers. Thiek-walled polyethylene bags are strong enough to withstand the plate's sharp corners and are available from lab supply houses in assorted dimensions a t a cost of about 2$ per beg.
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William N. Marmer Eastern Regional Research Center Agricultural Research Service
U.S. DepaRment of Agriculture PhiladelDhia, PA 19118
512
Journal of Chemical Education
