grams of adsorbent on 8- x 8-inch plates with a thickness of 1000 to 1100 microns could he readily prepared by the spray method. In preparing thick plates three consecutive coatings are sprayed on the plate and each layer is allowed to dry for approximately 2 minutes before application of the next. Figure 1 shows a silicacoated plate prepared with the spray procedure, and Figure 2 shows one prepared with a commercial applicator. Both plates were activated a t 130' C. for 11/*hours. A test mixture (Brinkmann Instrument Co., Great Neck, L. I.), consisting of 3 dyes (4-dimethylamino-azobenzene, indophenol, and Sudan Red G.), was applied to the plates and developed with benzene as solvent. Both plates required 40minutes to develop. Afourth spot a t the origin of application is ascribed to an impurity in the test mixture. ACKNOWLEDGMENT
The author is indebted to B. L. Van Duuren for suggestions and encouragement in this work. LITERATURE CITED
Figure 2. Thin layer chrornotogram of test mixture on silica gel plate prepared b y applicator technique
ber of plates can be prepared by varying the amount of slurry. Also, the ratio of adsorbent to r a t e r is not critical as i t is in the applicator technique. The spray bottle is held 7 to 9 inches from the snrface of the plate during
spraying. The nozzle should not be held too close to the surface of the plate; when this happens, irregularities or craters appear on the surface of the layer. Thick plates containing up to 20
Work was SuDDorted bv erant number C5946 from thk DepahGent of Health, Education and Welfare, U. S. Public Health Sekoe, National Cancer Institute.
Diethylamine-Ninhydrin a s a Color Test Aid in Identification of Amino Acids on Paper Chromatograms Richard Circo and Bob A. Freeman, Department of Microbiology, University of Chicago, Chicago 37, 111.
different color tests have M been published for the identification of amino acids on paper chroANY
matograms. While there is a t least one specific reagent for the color identification of each individual amino acid, relatively few universal reagents exist, which are capable of giving specific colors with a variety of amino acids and m
