Combined Ascending-Descending Paper Chromatography Thomas McCullough, CSC and Walter Rocabado St. Edward's University, Austin, TX 78704
The,following hrief paper describes a modification of paper chromotography that includes both ascending and descending flow using readily available equipment. Advantages of this technique: 1. The time for the run is reduced slightly. 2. Each spot with an Rf greater than 0.50 will have its own
channel and can he detected individually 3. Amuch longer flow distance is available.
blade. Their purpose is to prevent the flaps from touching the sides of the beaker and other parts of the paper. The Rf values from this combined ascending-descending procedure are not significantly different from those of ordinary ascending paper chromatograms. The dimensions indicated in the figure can he increased if longer runs are desired and larger containers are available. We thank the Welch Foundation for their financial support
Materials needed: 600-mL beaker 10 mL of developing solvent plastic covering and rubber band chromatogram paper (19- x 14-cm) solutions of knowns and unlmowns capillary spatter seven polyethylene tubing sections polyethylene clip
Procedure Using a soft pencil draw faint lines on the paper according to the figure. The dotted lines should he 2.0 cm apart and 2.0 cm from each paper edge. With clean scissors cut along the dotted lines to produce seven "flaps". Spot the paper with seven spots 2.0 cm apart so that they line up on the extended center line of each respective flap. Attach a polyethylene section to the free end of each flap. Fold the paper along the solid line and clip it to form a cylinder with the flaps hanging down on the outside of the cylinder. Place the cylinder, flaps and all, in the beaker and run the chromatogram. The polyethylene sections, about 1 cm long, can be cut from 5- or 6-mm tubing and slit lengthwise with a razor
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Diagram of layout for paper chromatogram.
Volume 69 Number 12 December 1992
995
