tritium samples for this purpose are easily prepared by the method of Wilzbach (2, 9).
part of it was introduced from the end of the combustion tube in a manner somewhat similar t o that used with many Dumas nitrogen combustion lines ( 7 ) .
DRY COMBUSTION OF ORGANIC COMPOUNDS
A T-stopcock is now provided a t the exit end of the absorption tube of the oxygen purification system, with ball joints on each of the exit arms of the stopcock (Figure 1). A 1l4-inch copper tube with brass ball joints is used to connect one of these exit arms to the side arm of the combustion tube, and a similar copper tube is led to the end of the combustion tube. Instead of a cap, the combustion tube is provided with a n adapter to permit it to be joined to the second copper tube. After introduction of the sample, oxygen is allowed to back-flush through the adapter for about 30 seconds; then the ball joint on the adapter is joined to that on the copper tube (which moves easily on the ball joint at the T-stopcock). The flow of oxygen is immediately started by adjustment of the stopcock at the exit end of the combustion tube, and the movement of the sample into the main combustion furnace is started. During the entire combustion, oxygen flows both through the side arm and down the entire length of the tube, thus eliminating any possibility of vapor’s being trapped in a closed pocket of the combustion tube. KOsamples have exploded since this system n a s put into use.
While the combustion system used in this laboratory for isotopically labeled organic compounds has proved generally satisfactory (3, 4),a problem arose during the combustion of very volatile liquids. Specifically, during the combustion of several samples of pentane and one of benzene, the sample exploded with sufficient violence t o break the combustion tube after the closing of the cap a t the end of the tube, and before the start of the oxygen flow through the trapping system. Cooling of the portion of the tube around the sample with dry ice did not solve the problem. I t was concluded that this effect rvas probably due t o slight volatilization of the sample into the closed pocket between the end cap and the entrance of the side arm carrying oxygen into the tube, and that in this static system the leakage of some vapor from the sample toward the heated zone of the main combustion furnace allowed a flash back to occur. This was solved by splitting the incoming ouygen stream so that
ACKNOWLEDGMENT
The authors acknolwedge the help of Karl Walther and Casimir Kawrocki in the design and construction of the quartz and metal counters described. LITERATURE CITED
(1) Bernstein, W., Ballentine, R., Rev.Sci.
Instr. 21, 158 (1950).
(2) Christman, D. R., Chemist Analyst
46, 5 (1957). (3) Christman, D. R., Day, X. E., Hansell, P. R., Anderson, R. C., ANAL. CHEM.27, 1935 (1955). (4) Christman, D. R., Stuber, J. E., Bothner-By, A. A , , Ibid., 28, 1345 (1956). (5) Christman, D. R., Wolf, A. P., Ibid., 27, 1939 (1955). (6) Fergusson, G. I., lVucleonics 13, Xo. 1, 18 (1955). (7) Kirsten, W.,ANAL. CHEAI.22, 358 11950): 25. 74 11953). (Si Van’Slyke, 6. D.,’Steele, R., Plazin, J., J . Bid. Chem. 192,769 (1951). (9) Wilzbach, K. E., Kaplan, L., Brown, W. G., Science 118, 522 (1953). (10) Wolfgang, R., Mackay, C. F., Nucleonics 16, N o . 10, 69 (1958). DAVIDR. CHRISTMAN CATHERINE 31. PAUL Chemistry Department Brookhaven Kational Laboratory Upton, L. I., N.Y. RESEARCH performed under the auspices of the U. S. rltomic Energy Commission.
Stable Diazo Salts for Chromatographic Spray Reagents SIR: For a number of years investigators in the fields of mood and plant chemistry and related fields have employed diazotized amine spray reagents for locating phenolic materials on paper chromatograms. Commonly used spray reagents include diazo reagents prepared from sulfanilic acid ( I ) , benzidine (S),and p-nitroaniline (2). I n all cases, diazo spray reagents, because of their instability, were prepared immediately prior to use by mixing a n acid solution of the aromatic amine with a solution of sodium nitrite. Even stock solutions of these amines are somewhat unstable, and fresh solutions must be prepared from time to time. I n the course of our work on the paper chromatography of wood lignins and extractives and their oxidation products we learned of the commercial production of stabilized diazo salts of many aromatic amines ( 4 ) . These dyestuff intermediates are water-soluble powders which are stable a t room temperature, even for years. One of the available salts was Fast Red Salt GG, a stabilized diazo salt of p-nitroaniline, one of the aromatic amines we employed
132
ANALYTICAL CHEMISTRY
in our chromatographic studies. Accordingly, chromatograms of 20 phenolic compounds related to wood chemistry were sprayed with a 0.057, solution of Fast Red Salt GG, and the colored spots produced upon spraying with sodium carbonate solution were compared with those produced from the same compounds sprayed with diazotized p-nitroaniline solution prepared in the usual manner ( 2 ) . Colors nere identical in all instances, but the normal background color (probably because of coupling of the diazo salt n ith some unchanged p-nitroaniline) obtained by the older method was absent. Thus, commercially produced stable diazo salts of a number of aromatic amines provide readily available spray reagents for locating and identifying phenolic compounds (and aromatic amines) on paper chromatograms. Furthermore, they obviate the necessity for mixing stock solutions immediately prior to spraying and for periodic preparation of fresh stock solutions. A complete paper with a table of colors obtained with 20 phenolic compounds
and 30 different commercial stabilized diazo salts together with spectrographic studies on the effect of concentration on the nature of the colored spots produced is in preparation and will be published shortly. ACKNOWLEDGMENT
The authors are indebted t o Antara Chemicals Division, General -4niline & Film Corp., for the sample of Fast Red Salt GG. LITERATURE CITED
(1) Bsldridge, R. L., Lewis, H. B., J . B i d . Chem. 202,169 (1953). ( 2 ) Brav. H. G., Thoroe. K.V.# Khite, ’ K., B”zochem.J . 46, $71 (1950). (3) Koch, J. E., Krieg, W.,Chem. Ztp. 62, 140 (1938). (4) Laughlin, E. R., Institute of Paper Chemistry, Appleton, K i s . , private communication. IRNIX -4.PURL PATRICI.~ F. McCoy
The Institute of Paper Chemistry Appleton, T’vis.
