J. N. BeMiller Southern
Illinois University Carbondole
In January 1963, three articles1-"ere published describing rapid demonstrations of thinlayer chromatography. Predating these articles is another describing TLC in test tubes.& I have used this latter technique with success in a simple, iuexpensive, and rapid laboratory exercise. The original article4 described coating test tubes with silicic acid in chloroform as follows: Test tubes, 13.5-15 mm id X 150 mm, are cleaned with chromic acid solution. A homogeneous suspension consisting of 1 part of silicic acid6 and 2.5 parts of chloroform (w/v) is poured into the tube. The test tuhe is allowed to stand about 5 sec in a vertical position. The coutents are then slowly poured out of the tube in one continuous and slow tilting motion. It is helpful to rest the open end of the tube on the lip of the receiving vessel during this part of the procedure. After most of the slurry has been discharged, the tube is held in an inverted position until almost all draining has stopped (abont 3 sec). The contents of the test tube should not be allowed to drain too long since this can result in a cracking of the thin layer deposit. The tube is then slowly tilted, without rotation, to a horizontal position and placed on a level surface until most of the solvent has evaporated. After the coated tube has air dried in the horizontal position, the top side is marked for future reference since it is the linear surface a t this part of the circumference which is employed for chromatography. An additional coating of silicic acid is deposited a t the lip of the test tube. The open end of the coated tube is immersed a t a 45' angle to a depth of about 5 inm in the chloroform silicic acid suspension. I n this position it is rotated slowly through one revolution to put an additional thin layer of silicic acid on
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Journal of Chemical Educofion
Test Tube TLC both sides of the glass. The coated tubes are then heated at llO°C for 15-60 min. I have found that an alternative method works equally well: A homogeneous suspension consisting of 1 part of silica gel6 and 2 parts of water is poured into the test tuhe. After 5 sec, the contents are poured out of the tube by tilting the tube rather rapidly. After most of the slurry has been discharged, the tube is held in an inverted position until almost all draining has stopped (about 5 sec). In this case, the bottom surface is the one to be used for chromatography and is marked. An additional coating of silica gel is deposited a t the lip of the test tube as described above. The tube is then placed in a horizontal position 15-ith the surface to be used up and heated a t 110-115°C for 1-2 hr. Pigment solutions can be prepared in several simple ~ a y s . 5 The ~ concentrated solution is applied with a capillary tube to the surface to be used, about 2 cm from the lip of the test tube. After 15-30-sec drying, the tube is inverted in a beaker containing the developing irrigant (about 1 cm deep). A number of irrigants can be used; benzene-acetone (7:3 v/v) works well. The inverted tube makes its own chromatographic chamber and gives excellent separation of components in abont 15 min. ANWAR, M. H., J. CHEM. EDUC., 40,29 (1963). E., OTT, D. G., AND PERRINGS, J. D., J. CHEM. HANSBURY, EDU,., 40,31(1963). ROLLINS. C., J. CAEM.EDUC., 40,32 (1963). 'LIE, K. B., AND NYC,J. F., J . Chromalog., 8,75 (1962). "ie and Nyc used reagent grade silieic acid (J. T. Baker Chemical co,) which passed through a 140- mesh Silica Gel G for thin layer chromatography from Brinkmann Instruments Inc.
