David Jordan State University of New York College at potsdam Potsdam, 13676
1I
Cylindrical Thin-Layer Chromatography
Recent laboratory manuals of organic chemistry1 am1 THIS JOURNAL^ have described experiments employing thin-layer chromatography (tlc). These micro-scale experiments have employed as plates microscope slides coated with adsorbent either by dipping in slurry or by the spreading of slurry. I would like to describe a n alternative modification of the tlc technique reported earlier3 that has been used to advantage in our laboratory for the separation and identification of dye mixtures. The adsorbent has been placed on vials (90 mm X 30mm diameter) by dipping the vials into suitable slurries. Inserting a vial into the neck of a small bottle of slurry by holding the lip of the vial has proven t o be much easier and neater than the dipping of slides. The resultant cylindrical tlc "plate" has a larger coated area (circumference 95 mm; height 85 mm) than that obtained on a slide plate (25 mm X 70 mm). On a slide plate, two samples spaced 10-12 mm apart might be analyzed simultaneously; on our cylindrical plate with the same sample spacing 7 or 8 samples might be analyzed concurrently and with possible better separation due to the greater distance of travel of the solvent front. This capacity for an increased number of samples permits analysis of an "unknown" by directly
510 / Journol of Chemicol Education
comparing it with as many as 6 to 7 standards. Aside from the increased adsorbent area of such cylindrical tlc plates and the ease of preparation and handling they may offer improved analytical precision. I n the development of a cylindrical plate the vial is placed a t the center of a beaker or jar containing solvent t o a depth of several millimeters. I n this concentric arrangement all points about a circumference of the plate are in contact 11-ith the same solvent atmosphere. Also, in that the cylinder has no vertical edge, "edge effect^"^ are eliminated and, therefore, all samples experience identical conditions. Variation of the vial size or the use of test tubes or bottles as cylinders permits the employment of cylindrical tlc on a variety of scales.
' (a) BALDWIN,JOHN,"Experimental Organic Chemistry," Ma~~onr~ McGraw-Hill, New York, 1965, p. 62. (b) CASERIO, C., "Experimental Organic Chemistry," W. A. Benjamin, New York. 1967. o. 1. ' fi ~vls,'i~~cHaE~, J. CHEM. EDUC., 45, 192 (1968). (b) HERZ, JOSEFE., J. CHEM. E D U C . ,599 ~ ~(1966). , =IICAN, R., A N D RAPAPORT, ELIEZER, J. CHEM. EDUC., 44, 296 i,A"". l O R 7 1,. ST.~HI.,EGON,"Thin-Layer Chromatography," Academic Press Inc., New York, 1965, p. 13.
