V O L U M E 22, NO. 8, A U G U S T 1 9 5 0 Table I.
1003
Blank Analyses of Carbon Black Weight Taken, Gram KO rubber present 0.0390 0.0622
Carbon Black Philblack 0 ( R F ) Sterling 99 (FF)
Ca. 0.14 gram of GR-S present Spheron 6 (MPC) 0.0514 Philblack A (HMF) 0.0752
Weight Found, Gram 0.0379 0.0607 0.0501 0.0746
Table 11. Analyses of Vulcanized Rubber Stocks Type of Rubber Natural Neoprene Type G N Butyl GR-8
Amt. of Filler, % 2 2.6
Inorganic Filler Zinc oxide Magnesium oxide Zinc oxjde Zinc oxide Zinc oxide
3.8 3.1 1.9
Nominal Carbon Av. Carbon No. Found, Deviation Black, of % of Mean, % Detna. (Av.) % .4ba. 30.4 7 30.5 0.21 23.6 5 23.9 0.21 28.8 28.2
3 5
28.6 28.3
0.13 0.20
gram in weight, were run through the entire procedure. To two of the samples, sufficient GR-Swas added to make the combined weight approximately 0.2 gram. It appears from the results given in Table I that no correction factor is necessary. Four specimens of cured rubber stock were analyzed by this
procedure. The authors are indebted to G. D. Louth of Firestone Tire and Rubber Company, who furnished the certified stock with information on the kind and amount of inorganic filler. The results of the analyses are given in Table 11. The average deviation of a single determination never exceeded 0.6% absolute. The method appears sufficiently accurate to recommend it for control work on rubber-carbon black master batches. LITERATURE CITED (1) Am. Soc. Testing Materials, “1946 Standards,” Part IIIB, Specification D 2 9 7 4 3 T , p. 941, D 833-46T, p. 976. (2) Barnes, R. B., Williams, V. Z., Davis, A. R., and Giesecke, P., INDENQ.CHEM.,ANAL.ED.,1 6 , 9 (1944). (3) Bauminger, B. B., and Poulton, F. C. J., Analyst, 74, 351 (1949). (4) Decker, P., Chem. Teekblnd, 39, 624 (1942). (5) Galloway, P. D., and Wake, W. C., Analyst, 71,505 (1946). (6) Kolthoff, I. M., Lee, T. S., and Carr, C. W., J. Polymer Sci., 1, 429 (1948). (7) Louth, G. D., ANAL.CEEM.,20,717 (1948). (8) McCready, J. E., and Thompson, H. H., IND. ENO. CHEM., ANAL.ED.,18, 522 (1946). (9) Tyler, W. P., and Higuchi, T.. India Ruhber T o d d . 116, 635 (1947). RECEIVED February 6, 1950. Work carried out under sponsorship of the Office of Rubber Reserve. Reconstruction Finance Corporation, in connection with the synthetic rubber program of the United States Government.
Comparison of Calcium 45 Oxalate and Carbonate Precipitates for Radioactive Assays RAY L. SHIRLEY, RILEY DEAL OWENS, AND GEORGE K. DAVIS Florida Agricultural Experiment Station, Gainsville, Fla.
Oxalate and carbonate methods have been compared with respect to preparation of suitable precipitates for radioactivity assays of calcium 45. Interference of magnesium, phosphorus, and aluminum was studied in regard to weight of precipitate and influence on activity measurements. Because of the common presence of inerfering ions, the oxalate method is indicated to be more satisfactory than the carbonate procedure for the preparation of calcium precipitates for radioactivity assays, especially in biological materials.
f l ALCIUM is customarilv Drecioitated from a solution of the
ash of biological materiais &9 (he oxalate ( 1 ) and in this form it is generally collected by filtration for radioactive assay of calcium 45 (3,4,6). In this investigation the oxalate method compared with a carbonate procedure for the preparation of suitable calcium precipitates that might be used for routine analysis of radioactive calcium 45 in biological materials.
that supplied by Tracerlab, Inc. (7). This equipment provides a very reproducible means for re aring precipitaces for ridioactive assay. The surface area o f a f precipitates was 2.835 s cm. ~ l - , mica-window i~ (1.5 to 2.0 mg. per sq. cm,) ~~i er-i&eller tubes were used in conjunction with commercial scafers for the activity measurements.
.
RESULTS AND DISCUSSION
In Figure 1, self-absorption curves show the rate at which tJhe calcium carbonate and calcium oxalate precipitates were found The oxalate procedure (1) requires heating approximately 50 to absorb the beta-particles emitted by the calcium 45. The ml. of a solution of the sample to boiling temperatur;, adding CdCiUm oxalate precipitates absorbed a few more per cent Of the m], of mturated ammonium oxalate, and then ad’ustlng the pH radiations than the carbonate precipitates of corresponding to the intermediate color of methyl red indicator (approximatel pH 4.8). In making wet digestions of bio1oe;ical materials w i d weight. This difference became greater as the weight of the p r b The self-absorption curves for both com~~~~~~~~e~~~ ~~~~~~p~ ~ ~ ~ ~ ~ r , “ ” , $ ‘ cipitates ‘ ~ ~ ~ increased. ~ pounds show a nearly linear dependence upon sample weights in .neutralize an aliquot of the di est with sodium hydroxide, add sodium carbonate, stir, let stan8 a few hours, and then filter the the range investigated in this studv. Some writers (, 8,. 6) , have carbonate precipitate. ’ TOevaluate this procedure recipitates of pointed-out the &airability of preiaring precipitates of “infinite thickness” in which a negligible number of beta-particles reach the surface from the bottom of the sample. In such precipitates The Drecititates were collected on Whatman NO.42 filter DaDer by Gems’ of a suitable funnel, ring, and disk assembly, s i d a q the observed counting rate is proportional to the specific activity. EXPERIMENTAL
tgt
~~~~~~~f
~~~~~’~~~~~~~~~~~~~~~~~~~~~~
ANALYTICAL CHEMISTRY
1004
As indicated in the self-absorption curves in Figure 1, the specific activity ia approximately a linear function of the weight of the precipitate throughout the range investigated, and precipitates that weigh more than 80 mg. are diacult to filter and transfer by the technique used in this investigation. Therefore, it is believed by the authors that for practical routine analysis it is easier to make corrections for self-absorption by such curves as those presented in Figure 1 than to prepare and handle precipitates of “infinite thickness.”
The values obtained for per cent dose by the two procedures are nearly equivalent except sample 7, where 25.32% waa obtained by the oxalate method, compared to 18.41% by the carbonate method. The carbonate procedure showed a little more total calcium to be present in the aliquots analyzed than was found by the oxalate method, except in samples 3 and 7, which were slightly lower. Although these data suggest that either method will give equivalent results on such biological materials as poultry excrement, because of the slow rate at which the carbonate solution filters, compared with that of the oxalate precipitate, the latter method is much to be preferred. Slow filtration was not experienced in the carbonate method on standard calcium samples that contained no added phosphorus or aluminum; this indicated that the carbonate procedure should find application in nonbiological materials or substances which do not contain significant quantities of interfering elements. SUMMARY
f
\
SOL-
301
4 MG.
Ib
IL
20
25
-
3L
PREOFiTATE PER CM!
Figure 1. Beta-Particle sorption
I
’
35
Self-Ab-
Preparation of suitable precipitates for radioactivity assays of calcium 45 by the calcium oxalate and calcium carbonate methods was studied. The oxalate precipitate was found to have greater capacity to absorb beta-particles than the carbonate precipitate. This was expected because of the difference between the average atomic numbers of the two substances. The difference in selfabsorption between the two types of precipitates is not great enough to affect size of samples required for routine analysis.
Curves obtained with radioactive calcium oxalate and caloium carbonate precipitate.
Table I. Interfering Elements. In biological materials the elements most likely to be present in sufficient quantities to interfere with either the carbonate or oxalate procedures are magnesium, aluminum, and phosphorus. Magnesium may be removed in the oxalate procedure by washing the precipitate with hot water (I). In the carbonate procedure 5 mg. of magnesium were found not to interfere in the weight of the precipitate, but caused a loss of approximately 25% of the radioactivity. The cause of this loss was not determined, but it may have been due to the magnesium altering the gross absorption coefficient so that the apparent activity was decreased by this amount. The oxalate method was not affected by 50 mg. of aluminum alone, but when this amount was present with 50 mg. of phosphorus, approximately twice the weight of precipitate was obtained as was expected from the amount of calcium present and there was a great decrease in the apparent specific activity of the precipitate. The increased weight of the precipitate waa probably due to precipitation of aluminum phosphate. However, samples containing up to 20 mg. of both phosphorus and aluminum were found to have no interference. In the case of the calcium carbonate precipitation, 5 mg. of aluminum were without appreciable effect,, but 50 mg. made filtration practically impossible. As little as 2 mg. of phosphorus caused interference in the carbonate method, particularly by increasing the time of filtration and decreasing the apparent specifioactivity of the precipitate. Analysis of Biological Materials. I n Table I data are presented that were obtained for (1)the per cent dose of calcium 45, and (2) the weight of total calcium found in equivalent aliquots of hen excrement by the oxalate and carbonate procedures. The metabolism studies made with the chickens using calcium 45 will be published elsewhere. The excrement samples were digested with concentrated nitric acid and made up to volume in volumetric flasks. Equivalent aliquots were taken for preparation of both the calcium oxalate and calcium carbonate precipitates. The values reported were calculated to represent the per cent of the administered calcium 45 excreted by the particular hen during the day that the excrement sample was collected. The hens had previously received single oral doses of the calcium 45 isotope.
Calcium 45 and Weight of Total Calcium Found in Equivalent Aliquots of Hen Excrement
sample
No; 1 2 3 4 6 6 7
Oxalate Prooedure Dose, % Ca, Mg. 0.23 0.15 0.17 0.51 0.64 0.87 25.32
Carbonate Procedure Dose, % Ca, Mg.
11.9 11.9 11.8 10.0 6,6
23.8 32.2
0.21 0.14 0.40 0.52 0.48 0.83 18.41
14.0 12.4 10.8 13.6 9.6 24.8 30.0
Interference of magnesium, phosphorus, and aluminum waa studied in regard to weight of precipitate and influence on activity measurements. Magnesium altered the gross absorption coefficient of the carbonate precipitate, but otherwise caused no interference. Both phosphorus and aluminum markedly interfered with the rate of filtration of the carbonate solution in the carbonate method. Phosphorus caused a decrease in the apparent specific activity of the carbonate precipitate. In the case of the oxalate procedure, aluminum and phosphorus caused no interference when present alone, but when present together in the range of 50 mg. each, large discrepancies in weight of precipitate and in apparent specific activity were observed. Because of the common presence of interfering ions, the oxalate method is indicated to be more satisfactory than the carbonate procedure for the preparation of calcium precipitates for radioactivity assays, especially in biological materials. LITERATURE CITED (1) Assoc. Offic. Agr. Chemists, “Official and Tentative Methodr of Analysis,” 6th ed., 1945. (2) Aten, A. H. W., Nucleonics, 6, 68 (1950).
(3) Bledsoe, R. W., Comar, C. L., and Harris, H. C., Science, 109,329 (1949). (4) Driggera, J. C., and Comar, C. L., Poultry Sci., 28, 420 (1949). (5) Schweitzer, G. K., and Whiteny, I. B.,“Radioactive Tracer Techniques,” New York, D. Van Nostrand Co., 1949. (6) Spinks, J. W. T., Berlie, M. R., and O’Neil, J. B., SCince, 110, 332 (1949). (7) Tracerlab, Inc., Boston 10, Mass., Tracerlog, 22, 9 (1949).
RECEIVED April 28, 1950, Publiahed with the permiasion of the director of the Florida Agricultural Experiment Station.
