A CHROMATOGRAPHIC CHAMBER FOR THE STUDENT LABORATORY DONALD 8. WlGGANS University of Texas, Southwestern Medical School, Dallas, Texas
A VARIETY of methods have been proposed for the introduction of the technique of paper chromatography into student laboratory courses. It is desirable for a successful procedure to meet several criteria: The method should he suitable for large numbers of simultaneously developing chromatograms with a minimum amount of extra equipment and glassware; the filter paper support should be wide enough for several spots to ascend in parallel paths in order that direct comparison of R, values may be made on the same sheet; the chromatographic tank should be of sufficient height for hhe effective separation of components of applied solutions; the mechanism of the apparatus should be of minimum complexity in order that the emphasis of the experiment is placed upon chromatography and not upon complicated equipment. The construction of an effective chromatographic tank, which meets the listed criteria, can he accomplished by means of two beakers of the same size. A self supporting ascending paper chromatogram is prepared by conventional techniques of spot application and held in cylindrical form by means of staples. The vertical edges of the standing cylinder must not touch or overlap. After placing the developing solvent in the lower beaker, the paper cylinder is lowered into the beaker and centered so that no contact will occur with the walls of the heaker. The second beaker is inverted carefully over the cylinder and lowered until it rests upon the first beaker. A circumferential band of cellophane tape a t the junction of the tops of the beakers provides support for the glassware and seals the tank to maintain a constant atmosphere. It is advisable to use a series of short pieces of tape for ease of manipulation. A more
simple sealing process is possible hen the pourouts are not aligned. A modification of the procedure permits a saturated atmosphere to exist in the tank prior to the addition of the developing solvent. A small third beaker containing the desired liquid is first centered in the lower beaker. The cylindrical chromatogram is then placed around the small beaker in concentric fashion, and the tank is completed and sesled. After a suitable time for equilibration within the tank, a small piece of tape is removed in the area of the pourout of the lower beaker. The solvent is then introduced through this opening directly to the bottom of t,he tank by means of a drawnout capillary pipet. The size of the chromatogram is limited only by the size of the beakers. A 9- X 10-in sheet, with the vertical dimension of 10 in., can be accommodated in a tank prepared from 800-ml. beakers and will provide sufficient area for 8 or 9 different,spots to ascend a maximum of 9 in. from a base line which is 1 in. from the lower edge of the paper. Four chromatograms of this size can he cut conveniently from a sheet of Whatman No. 1 filter paper, 18'/4 X 2Z1/, in. Correspondingly larger or smaller chromatograms may be prepared in accordance with the size of available beakers, the rate of ascent of the solvent, and the duration of the experiment. Two-dimensional chromatograms can be conveniently handled in the chamber using square sheets of filter paper. If an experiment is chosen in which pigmented materials are being separated, visual observation of the developing chromatographic pattern is possible. The procedures as described have proved successful in the student laboratory.
JOURNAL OF CHEMICAL EDUCATION
