shown in thermogram A and the boiling endotherm of n-propylamine shown in thermogram B are both absent from thermogram D. Instead, a complex thermospectrum appears, indicating a stepwise reaction with endothermic and exothermic effects overlapping. On the other hand, thermogram E of the mixture of dextrose and di-n-propylamine shows distinctively the boiling endotherm of the amine at 113’ C. and the melting endotherm of dextrose at 158’ C. as compared t o thermograms C and A , respectively. No reaction between these two is apparent. The use of differential thermal analysis t o study chemical reactions is not new (3, 4,6). Bollin and Kerr used a similar technique for pyrosynthesis of minerals from their constituents (1). Great potential exists in applying this
technique for the identification of an organic compound (including polymers), first b y its own thermogram, and then b y the thermogram of its reaction with a specific reagent. Compared with the classical method, the thermal dynamic approach is less time-consuming, uses only small amounts of sample and reagent, requires less analytical skill, and provides more characterizing features. In addition t o determining the melting point of the principal derivative, the new technique reveals products other than the derivative, and supplies information on the over-all reaction. LITERATURE CITED
(1) Bollin, E. &I., Kerr, P. F., Am. Mineralogist 46, 823 (1961). (2) “Handbook of Chemistry and
Physics,” 43rd ed., Chemical Rubber Publishing Co., Cleveland, Ohio, 1961. (3) Mackenzie, R. C., Utchell, B. D., Analyst 87, 420 (1962). (4) Murphy, c. B., h 4 L
. CHEM. 30, 867 (1958); 32, 168R (1960); 34, 29812 (1962). ( 5 ) Shriner, R. L., Fuson, R. C., Curtin, D. Y., “Systematic ,,Identification of Organic Compounds, 4th ed., Chap. 9 and 10, Wiley, Sew york, 1956. (6) Smothers, W. J., Chiang, Y., “Dif-
ferential Thermal ilnalysis. Theory and Practice,” Chemical Publishing Co.,
New York. 1958. ( 7 ) Stinlson,’ H. F., J . Res. at^ B U T . Stds. 65A, 139 (1961). (8) Vassallo, D. A., Harden. J. C., ASAL. CHEM.34; 132 (i962). ‘
J E NCHIU Plastics Department E. I. du Pont de Seniours & Co., Inc. Wilmington, Del. RECEIVEDfor review October 2 , 1962. Accepted October 22, 1962.
Radiometric Analysis of Metals Using Chelates Labeled with ~ a r b o n - 1 4and Liquid Scintillation Counting Procedures SIR: The liquid scintillation counting procedures by eliminating the problem of self-absorption make i t convenient to use C14 for radiometric analysis. The degradation of 2,3-diketogulonic acid by some animals yields COz and oxalic acid. T o follow the first reaction a method was developed in which the C1 labeled with CY4 of the diketo acid was collected on a paper impregnated with KOH and counted directly in a scintillation solvent (1). Furthermore, the count rate was not affected b y the size of the paper or the number of the spots in which the activity was applied on the paper. When the paper was dried, the efficiency increased and there was no problem of self-quenching or infinite thickness over a very large range. Labeled oxalic acid was detected b y precipitation with calcium, and the paper on which the precipitate was collected was counted directly in a scintillation solvent. This generated the idea of reversing the process t o detect calcium or other alkaline earth metals using oxalic acid labeled with (214. The counting of radioactive samples adsorbed on filter paper and wet in scintillation solvents was summarized before by Funt ( 2 ) .
Different amounts of calcium (40 t o 200 microns) were precipitated in acetate buffer p H 5 with 1 drop of 0.5N oxalic acid containing 2 mg. of labeled oxalic acid in 10 ml. of the stable acid. Then the precipitate was collected on a paper b y filtration under vacuum and washed with a mixture of ammonium oxalate and oxalic acid. The paper (4 cm. in diameter) was carefully transferred t o a vial and dried for 40 minutes at 65’ C. Then 20 ml. of
the following scintillation solvent was added: 4 grams of 2,5-diphenyloxazole and 0.1 gram of 1,4-bis-2-(5-phenyloxazoly1)benzene t o 1 liter of toluene and counted at -8’ C. The results demonstrate a linear relationship between the count rate and quantity of calcium present (Figure 1). Duplicate analyses agreed within 10% of each other, but this value could be improved b y sealing the paper with saran (3) or better with some plastic insoluble in toluene. The possibility of measuring the total calcium and C45 in the same sample using a 2-channel analyzer is under study. It was the idea of the endorser t o call attention t o the possibility of increasing the sensitivity of any radiometric analysis in which it is worthwhile to use a 8emitter and a liquid scintillation counter procedure. LITERATURE CITED
40
80
120
160
200
ygms. OF CALCIUM
Figure 1. Relationship between the amount of calcium vs. c.p.m. of C14 oxalate
(1) Chiriboga, J., Roy, D. N., Nature 193,4816 (1962). (2) Funt, B. L., Can. J . Chem. 39, 711 (1961). ( 3 ) Grimes, E. T., AXAL. CHEM.34, 9 (1962).
JORGE CHIRIBOGA University of Tennessee Atomic Energy Commission Agricultural Research Laboratory Oak Ridge, Tenn. VOL. 34,
NO. 13, DECEMBER 1962
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