linearity at low concentrations of boric oxide with Procedure B. For the conditions specified, the intercept and slope of the calibration curve are about -0.38' and f0.0063' per mg. of boric oxide, respectively. For best results with Procedure B, the concentrations of sodium hydroxide and mannitol should be equal, on a molar basis. Then steady rotations are achieved within a few minutes after mixing, the calibration curve is linear, and relatively high sensitivity is realized. If the concentration of sodium hydroxide greatly exceeds that of mannitol, rotations change significantly with time of standing, the rate of change increasing as the hydroxide concentration increases. The observed changes in rotation are much larger than can be accounted for by extraction of boron from the container and must result from slow attainment of equilibrium. Even under the strongly alkaline conditions existing in Procedure B, borohydride hydrolyzes a t a significant rate. For the conditions specified, rotations increase a t the rate of about 0.001 to 0.002' per minute, and hence, should be measured promptly after mixing. The following results obtained in the analysis of sodium borohydride samples illustrate the applicability of the method. The analysis of duplicate samples of one lot of impure sodium borohydride weighing 3.144 and 3.071 grams gave values of 4.22 and 4.35% boric oxide, respectively. Two addi-
tional analyses of the same lot using samples weighing 1.524 and 1.936 grams, but with 90 and 45 mg. of added boric oxide, respectively, showed a total boric oxide content of 157 and 131 mg., respectively. After the weight of added boric oxide is subtracted, these values correspond to 4.39 and 4.44% boric oxide in the original sample. The average of the four determinations is 4.35% boric oxide with a standard deviation of *0.09%',. A sample of the purest sodium borohydride available to us was found to contain 0.23 mg.-atom of borate boron per gram by polarimetric analysis. Very careful determinations of total boron and of hydride hydrogen in this sample gave values of 26.16 and 103.3 mg.-atoms per gram, respectively. The value obtained for hydride hydrogen indicates that the sample contained 25.83 mg.-atoms of borohydride per gram, leaving 0.33 mg.-atom of boron presumably in the form of borate, which agrees well with the polarimetric measurement. A similar analysis on a less pure sample gave values of 23.69, 91.07, and 0.84 mg.atom per gram for total boron, hydride hydrogen, and borate, respectively. The concentration of borate calculated by difference from the total boron and hydride hydrogen determinations is 0.92 mg.-atom per gram, in good agreement with the value of 0.84 obtained by polarimetric determination. Although the methods described above are only about one fifth as sen-
sitive as the Rosenheim and Leyser method, they are more generally applicable and less subject to interferences than the latter. LITERATURE CITED
(1) Boeseken, J., "Advances in Carbohydrate Chemistry,,' Vol. 4, pp. 189210, W.W. Pigman and &I. L. Wolfram, eds., Academic Press, ?Jew York, 1949. (2) Isbell, H. S., Brewster, J. F., Holt,
N. B., Frush, H. L., J . Research Natl. Bur. Standards 40, 129 (1948). (3) Pecsok, R. L., J . Bm. Chern. Soc. 75, 2862 (1953).
Rosenheim. -4..Levser. F.. Z. anora. allgem. Chem: 119, ("1921). ' (5) Ryss, I. G., Slutskaya, h1. M., Zhur. Fiz. Khim. 21, 549 (1947). (6) Terechov, P., Collection Czechoslov. Chem. Communs. 1, 551 (1929). ( 7 ) Wamser, C. .4.. J . Am. Chem. Soc. 70, 1209 (1948) 14) \
-I
DOSALD D. DEFORD
ARTHUR S. BLONDER' ROBERTS.BRAN AN^
Department of Chemistry Northwestern University Evanston, Ill. RECEIVED for revieiv September 26, 1960. Accepted Decemher 21, 1960. Research supported by Callery Chemical Go. under a contract with the Bureau of k r o nautics, Department of the Xavy. 1 Present address, Department of Biochemistry, Northwestern University Medical School, Chicago, Ill. 2 Present address, Arniour Research Foundation, Chicago, 111.
Determination of Carbon, Oxygen, and Silicon in Solids by Activation Analysis with 15-M.e.v. Deuterons SIR: We have carried out experiments to test the possibility of determining small amounts of carbon in pure silicon dioxide by means of radioactivation with cyclotron deuterons of 15 m.e.v. The results show that it is feasible to determine as little as a few tenths per cent of C in Si02 by counting induced positron radioactivity in the bombarded sample without chemical processing. From the data the ratio of Si to 0 may also be estimated. The principal limit on the sensitivity for detecting C is the large amount of 0 present; for samples lower in 0 the sensitivity should be much better. In our experiments we used the stationary external target of the M.I.T. Cyclotron, a water-cooled A1 block upon which solid target materials approximately 10 cm. long and 1 em. aide can be placed. Five specimens Tere bombarded simultaneously in small A1 capsules machined from A1 rod to 0.33 mm. (89 mg./sq. cm.) wall thickness 472
ANALYTICAL CHEMISTRY
and held in place by covering with 0.0017-inch (11.6 mg./sq. em.) Dural foil. Specimens were 15 mg. of powdered material, and within each specimen the deuteron energy ranged from about 8 m.e.v. (reduced from an initial 15 m.e.v. by absorption in the covering foil and capsule wall) to 0 m.e.v. According to nuclear data summarized by Koch ( I ) , in this energy range the important nuclear reactions are C'*(dJn)NL3,016(d,n)F17J017(d,n)F18,0'8 (d,2n)F18,Si*g(d,n)P3*,and Si30(d,p)Si31. The ratio of C t o 0 is determined by analysis of a decay curve of annihilation positron activity induced by a short deuteron bombardment of the sample and comparison standards. The components 1.1-minute F1', 2.5-minute P30, 10.0-minute "3, and 112-minute F18, all pure positron emitters ( 2 ) , may be resolved, and the relative counting rates of 10.0-minute N13 and 112minute Fl* are a measure of the ratio of C to 0 in the sample. The ratio of
0 to Si is determined by counting the specimen simultaneously with y-scintillation and p-proportional detectors, mounted on opposite sides of the specimen position, for the relative activities of 112-minute F1s and 157-minute Si3I, a negatron emitter with virtually no y in its decay (g). Interference of the 0.65-m.e.v. p+ of FIB in the measurement of the 1.48-m.e.v. 8- of Si31 is eliminated by means of an A1 absorber of 250 mg./sq. em. Figure 1 is a plot of the counting rate ratio of N13 to PI8 for 5 specimens of SiO, nith varying content of C (as Sic). Bombardment was carried out for 1 minute, and the specimens were immediately transferred from the bombardment capsules to planchets for counting. A single channel scintillation spectrometer was centered on the 0.51-m.e.v. annihilation r-photopeak, and the measured activities were extrapolated to the time a t which bombardment ended. The resulting decay
species had decayed to negligible levels. The precision of the determination within each set of specimens bombarded simultaneously is a few per cent. It is believed that much of the scatter could be reduced if identical deuteron energies within each specimen were ensured by using bombardment capsules machined with high precision. In general, this technique can be extended to any nonvolatile matrix, and for many materials analyses may be performed by counting induced radioactivity without chemical processing. A detailed description of the present work is given by Winchester (3).
Table 1. Relative Counting Rates of 157-Minute Si3I to 112-Minute F1* /3* in Deuteron Bombarded S i 0 2
Bom-
1 2 3 4 5 6
0.93, 1.03, 1.03 1.03, 1.01, 1.02, 0.94, (0.69)” 1.09, 1.11,0.94, 1.00,0.85 1.03. 1.02, 1.02, 1.01. 0.92 0.98; 0.94; 1.06’ 0.99, 1 . 0 1
a Quartz sample from different source than the other four samples. Not included in average.
‘
F.
I30
/
-
LITERATURE CITED
curve, measured from 20 minutes to
4 hours after bombardment, shows only the 10.0-minute NI3 and 112-minute FIE components which are resolved graphically. Owing to the higher relative isotopic abundance of C12 over 0’’ and OlS, the XI3 component is prominent even for low carbon contentse.g., in the analysis of SiOz containing 0.2% C the counting rate of N1s exceeds that of F*8up to 1 hour after bombardment. The relation between the C/O and X13/F18 ratios is linear. These data also shon- a small activity of N13 where no S i c has been added; this may be due in part to impurity of C initially present in the SiOz and in part to failure to eliminate completely interference from the nuclear reaction 016(d,n~)X13. the threshold of which is 8.4 m.e.v.
SIR: Because of cross interference in analysis for nitrite (6) and 2-nitropropane (6) preliminary separation of the components in an appropriate solvent is required. In part this cross interference might be expected since the coupling of Znitroalkanes to form azo compounds is known (4). However, consideration of i t is not apparent in the determination of either nitrite formation by extracts of pea plants from 2nitropropane (6) or of nitrite formation for the determination of nitroethane oxidase actimty ( 3 ) . PROCEDURE
Aqueous solutions (1.5 ml.) containing nitrite and the 2-nitropropane were extracted with 1 to 5 ml. of heptane or benzene. Nitrite ion was determined on an appropriate aliquot (2.0 to 35.0
J ~.
~~
IC
3-
20
~
C Y
~
52
Corbo‘ &I
Figure 1. tures
3r)qen
lox
Analysis of S i O r S i C mix-
Table I gives the relative counting rates of p- from Si3I and 0.51-m.e.v. annihilation y from F18,induced by short deuteron bombardments in SiOZ, compared to the ratio Si/O and normalized to the average value. A thin A1 absorber was used to eliminate interference of Fl8 p + in the measurement of the more energetic 0- of Si31 by an endwindon proportional counter, and counting was performed a few hours after bombardment when shorter lived
mpmoles of nitrite) of the aqueous layer by the sulfanilamide method ( 5 ) . For the work reported here readings mere made in a Klett-Summerson colorimeter with the green (No. 54) filter, and sodium nitrite was used as a primary standard. For determination of 2-nitropropane, the hydrolysis method of Sweet et al. (6) was applied to the organic extract. Adaption of this method to the lower concentrations of nitro compounds required reduction of volume and modification of procedure. Thus: to an aliquot of the organic layer containing 2-nitropropane (0.2 to 22.0 pmoles), 5 ml. of water and 1.0 ml. of 6.3M NaOH were added. The well shaken mixture was allowed to stand for 10 minutes, after which 0.5 ml. of 30% hydrogen peroxide was added. The mixture was heated in a loosely stoppered tube for 1 to 1.5 hours in a
(1) Koch, R. C., “Activation Analysis Handbook,” Academic Press, New York, _ 1960. _ (2’1 Strominner. D.. Hollander. J. M.. Seaborg, 6. T., Rev. Mod. Phis. 30, 585 (1958). “Table of Isotopes.” (3) Winchester, J. W., “The Use of 15 \-I
h1.e.v. Deuterons for the Determination
of Carbon, Oxygen, and Silicon in
Solid Materials by Radioactivation Analysis,” Technical Rept., Dept. of Geology and Geophysics, M.I.T., Cambridge, Mass., October 26, 1960. JOHNW. WINCHESTER MICHAEL L. BOTTINO Department of Geology and Geophysics Massachusetts Institute of Technology Cambridge 39, Mass. RECEIVED for review November 17, 1960. Accepted January 3, 1961. Work supported in part by a contract with the AVCO Corp. and by a grant from the National Science Foundation.
water bath. After cooling, the sample was brought to 10 ml. and the nitrite ion formed mas determined as above on a 1.0- or 0.1-ml. aliquot for the range of 0.2 to 2.2, and 2.2 to 22.0 pmoles, respectively. For these concentrations the care in increasing the temperature of hydrolysis has not been as essential as the original method indicates. RESULTS
Indication that %nitropropane interferes with the sulfanilamide determination of nitrite is shown in Figure 1. For any one concentration of nitrite ion the amount of interference is not a function of Znitropropane concentration. Interference was also observed when the ratio of concentration of nitrite and 2nitropropane was 1:1 or 1000:1 as well as 1:1000 as shown in the figure. VOL. 33, NO. 3, MARCH 1961
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