Aluminum Plates for Thin layer Chromatography Fred Snyder, Oak Ridge Institute of Nuclear Studies, Medical Division, O a k Ridge, Tenn. HE SUBSTITCTIOX OF aluminum plates T f o r glass plates in thin layer chromatography (TLC) offers certain advantages x h e n one is interested in visualizing the components by HzS04 charring. Aluminum plates are heated directly on a hot plate where the rate of heating is controllable while the changes in color are easily and quickly visible. Obviously, Tyith aluminum, concern over breakage is unnecessary. This note provides information on the source and cost of aluminum, and the way in which the thin layer of silica should be applied. We have used alu-
minum sheet alloy 6061-T6 mill finish (4 mm. thick) obtained from the J. M. Tu11 Metal and Supply Co., Inc., Atlanta, Ga. The price of this aluminum is $2.21 per square foot. The aluminum plates are machine-cut in our instrument shop to the same size as the glass plates (20 x 20 em.) normally used for TLC. Aluminum of this type must be thoroughly polished with Brillo soap pads (Brillo Mfg. Co., Inc., Brooklyn, N. Y.) before routine washing and the application of silica layers. Twenty-five grams of Silica Gel G is mixed with 50 ml. of approximately 47y0
E T O H (1:1v./v. HzO:95y0ethanol) in a glass beaker, After mixing for about 30 seconds the slurry is poured into a thin layer applicator designed for the application of an approximately 250micron layer. The alcohol serves as a wetting agent, necessary for the uniform application of silica to aluminum. R e have also found it desirable t o use a Scotch tape strip on the bottom surface of the leading edge of the applicator, since it is othern-ise possible t o scratch the aluminum plates. UNDERContract with the U. S. Atomic Energy Commission.
Acidity Distributions in Cracking Catalysts Ralph J. Bertolacini, Research and Development Department, American Oil
cracking proB ceeds primarily by a carbonium ion mechanism t h a t is induced b y ECAUSE
CATALYTIC
acidic groups on the catalyst surface ('7'1, the determination of acid strength distributions in cracking catalysts has received considerable attention ( 1 , 2, 5 , 8). The usual techniyucl involves a series of titrations of the sample in nonaqueous medium n ith standard n-butylamine solution (1). The acid distribution is determined b y using Hammett indicators of varying pK, values (4). I n the titration with each indicator, the end point is reached by successive approximation using about seven catalyst samples. The sample-titrant system is stirred mechanically, and allowed to reach equilibrium over a time period of 4 to 24 hours. Although this method is reproducible. i t requires many titration
