Table II.
Tube Oxygen, Lot number p.p.ri. B
Table 111.
Relation of Oxygen Pickup to Time
7
88O
93, 9Sb 89
Lot Ba
Sample weight, grams 0.66 0 . 6 6 , 1.29 0.79
a
Relation of Oxygen Pickup to Pressure
Tube number
Oxygen, p.p.m.
Sample weight, g
Pressure, torr
8
194, 209 127, 117
0.59, 0.60 0.74, 0.77
2 4
x x
10-3 10-4
Same lot as in Tables I and 11, 90 p.p.m. oxygen.
Procedure as in Table I. Triple distilled mercury, 24 hours hold. c Oxifier reclaimed mercury, 24 hours hold. a
b
closed, and approximately 15 ml. of mercury is admitted to the extraction system and the magnetic bar manipulation is repeated. The wash mercury is removed as before. A total of five similar washes is made to remove completely the potassium amalgrtm; approximately 700 to 900 grams of mercury are used in all. The glass extraction portion of the system is brought to atmospheric pressure and the extraztion system and amalgam receiving flask are removed. U p to this point, the total time for the operation is approxirr ately 1 hour. The potassium is extracted from the amalgam using boiled distilled water and titrated with standard sulfuric acid to determine the weight of alkali sample used. The potassium oxide is washed out of the extraction chamb:r using boiled distilled water and titrated with standard 0.005.Y sulfuric acid using a microburet. Methyl red is used ,is an indicator in both titrations. The following vdues for oxygen content, Table I, clearly indicate a good degree of reproducibility. Each set of analytical values represents replicate potassium samples extruded from the same sample tube. To establish whether the amalgam
-METAL EXTRUDER
HOT
WIRE CUT-OFF hECHANISM-.
-SAMPLE
-
WASTE TRAVF’
70 HERCURV
RESERVOI
-
CONTAINER
TO VACUUM PUMP
ATE VALVE
TO VACUUM PUMP
-O-RING
JOINT
GLASS COVERED MAGNETIC BAR2
Figure 1 . apparatus
Alkali
TO VACUUM PUMP
metal
analytical
would react with the glass extraction system as a function of time, resulting in oxygen “pick-up,” three tests were performed. The alkali metal was extruded and amalgamated as usual. Then prior to extraction, the amalgam was retained in the extraction system for 24 hours. The oxygen values obtained, as shown in Table 11, indicated no dependence an residence time in the extraction system, up to 24 hours (the longest time studied). If our contention is correct, that a high vacuum analytical system is necessary for reproducible results, it follows that a poor vacuum would be a
source of positive error. Tests performed at 2 X l o + and 4 X 10-4 torr confirm this. The oxygen values obtained are given in Table 111. It has been long recognized that it is difficult to ascertain the accuracy of the amalgamation technique because of technical problems associated with adding known increments of oxygen to potassium metal. This problem still has not been overcome; however, the analytical results presented here demonstrate that good precision can be obtained if the amalgamation technique is used a t a pressure between 2 x 1 0 - ~ to 4 X lop6torr. After completion of our partial investigation, we received a translation of a Russian report (1) describing their amalgamation technique in a vacuum environment. LITERATURE CITED
i l i Malikova. Y . D.. Turovtseva > 7. M -Anakz Gazk V Metalakh Akad. S a d SSSR (Enqlash Transl.) FTD-TT-621338, 1962.(. 2.) PeDkowitz*L. P.. Judd. W. C.. ANAL. CHEM.22, 1283 (1950).
WILLIAMA. DUPRAUJUDSON W.GRAAB F. GAHN RANDALL Lewis Research Center National Aeronautics and Space Administration Cleveland, Ohio
Determination of the Deuterium Content of a Sample of Deuterium Oxide by Three Methods SIR: I n the hydrogen isotopic analysis of TzO in this laboratory, Tz resulting from the reduction of T20 by hot iron is analyzed on a mass spectrometer. Corrections must be made for small amounts of hydrogen introduced in the reduction, and the mass spectrometer must be carefully conditioned. This method was used in recent measurements of the densitv of liquid T2O (a), where accurate lrnowledge of the hydrogen-tritium :omposition is necessary. It was desirable to get an idea of the absolute accuracy of the particular technique by applying it to DzO where the isot ,pic composition can be independently determined by the
density and nuclear magnetic resonance (determination of protium) methods. A similar method using zinc ( 7 ) has been described in detail. Magnesium (9) has also been used as a reductant. The low volatility of iron is an advantage and it does not react with glass. =ilso, by partial oxidation of the iron, the same system can be used for interconversion of D? (T2) and DzO
(TzO). EXPERIMENTAL
R e duc t i on-M a s s S p e c t r o m e t e r Analysis. Transfers from the DzO supply t o analytical equipment were made in a d r y box; vessels and sy-
ringes were conditioned with D20. A 5-gram portion was attached to a vacuum system, brought to 20.0’ C. and a small fraction vaporized into a 500-ml. volume. T h e 10-ml., S T P vapor sample was isolated from t h e bulk of the sample with a mercury cut-off, condensed with liquid nitrogen into a reduction section (see Figure I), isolated with a mercury cut-off, and reduced with powdered Fe (0.5 gram) a t 500’ C. The resulting Dz gas was continuously removed through a palladium valve (500’ C.) with a Toepler pump into a storage bulb, without contact with stopcock grease (a necessary precaution with TzO). Following complete decomposition, the DP gas was compressed into a sampling bulb VOL. 36, NO. 2, FEBRUARY 1964
431
FURNACE PALLADIUM T H I M B L E IR" 0 . 0 . x 3" 0.010" WALL
PALLADIUM WELD KOVAR
GLASS-QUARTZ GRADE0 SEALS
OUIRTZ FRITS I MM X 10 HM
0.5 GH IRON-IRON OXIDE
HI-CUTOFF FROM 500 ML VAPOR BULB
QUART*d I I BOROSILICATE GLASS
Figure 1. paratus
Iron
decomposition
ap-
for immediate mass spectrometer analysis. The 0.5 gram of 250- to 325-mesh carbonyl iron (partly oxidized for our purposes; see blank correction below) was retained between quartz frits sealed into a vertical quartz tube (Figure 1). A temperature of 500' C. is roughly optimum for reduction rate. At toohigh temperatures the rate drops due to sintering. The 2-hour reduction time might be lowered by relaxing the condition of continuing until no further Dz is formed (to eliminate the effect of isotopic differences in rate). The upper frit might also be removed, more palladium surface provided, and the pressure of the system increased with a mercury piston, especially toward the end of the reaction. Only a few minutes are needed for analysis on a suitably conditioned mass spectrometer. The success of the method depends on careful conditioning of the decomposition system and the mass spectrometer. Conditioning of the system was accomplished by repeated exposure under operating conditions to high purity DzO and D B until the correction for introduced protium became constant. This correction for increase of the hydrogen atom fraction of the sample, A N H , was based on experiments using 99.5y0 Dz gas. Contributions to AXH were determined separately for the following steps: (1) passage of gas through the palladium valve and collection system; ( 2 ) reaction with the iron; and (3) contact of the vapor with the glass of the apportionment and storage sections of the system. To measure item ( l ) , 10 ml. of DZ gas was transferred by a Toepler pump into the cold iron reactor, passed through the palladium valve and reanalyzed; ANE amounted to 0.0001. Item (2) was measured by oxidizing 10 ml. of analyzed Dz gas to DzO (with the iron oxide present with the iron), then decomposing the DzO, collecting and again analyzing the D2. The oxidation of Dz was made complete by condensing the D 2 0 with liquid nitrogen. The increase in S H (0.0011) minus 0.0001 due to collection (item I.) was halved 432
ANALYTICAL CHEMISTRY
(since hydrogen is picked up both in making and decomposing DzO), giving 0.0005 for item (2). The third source of degradation was found to be zero as follows: 10 ml. of analyzed Dz,gas was converted to DzO with the iron oxide, the DzO was sublimed to a storage vessel, allowed to stand for a short time, vaporized essentially completely into the 500-ml. volume, and processed as in (2). AA'E was 0.0011 so that item (3) is zero. Thus for a standard 10-ml. vapor sample of DzO the total A.%'H correction was 0.0006 + 0.0002 [standard deviation based on several determinations of items ( l ) , (Z), (3)]. Item (2) was run before and after an analysis of DzO. The total ANH for TzO was 0.0009. The Consolidated-Nier Model 201 mass spectrometer was thoroughly baked and conditioned with DZ to get results which did not change with further conditioning. When a second mass spectrometer of the same model was used, the deuterium content was 0.06% lower. The second inrtrumrnt responded less satisfactorily to conditioning than the first. The same behavior with the second spectrometer was observed in the analysis of TZgas. Results from the second instrument were ignored. The mass spectrometric analysis of the DZ gas was increased by 0.0006 ( A N H ) to get the deuterium atom fraction, .V\, of the vapor in equilibrium with the original liquid. The desired deuterium atom fraction of the liquid, SI, was obtained (10) by means of the relation NI/(l - NI) =
''*
[ - V L / ( ~- ~ Y S )[ ]P a H ~ O / P o D ~ O I
(1)
P o ~ z ~ / f 'iso 1.154 ~ z ~ at 20.0' C. (6). For N , , = 0.9981. N r is 0.9982 a t 20.0' C. The cornposition of the 5 grams of DzO was unaffected by the removal of the vapor samples. DzO Analysis by Density. Density measurements were made a t 25.00' C. with a 10-ml. quartz dilatometer which had been calibrated with conductivity water. The precautions of Bauer ( I ) were followed. The solids content of the DzO was less than 1 part in 106. Oxygen isotope analyses by the COZ exchange method (8) gave 0.374 i O . O O l ~ c 0 ' 8 for the DzO and 0.199 + O . O O l ~ c 0 1 8 for the conductivity water. The calculation of the isotopic composition of DzO from the density and isotopic oxygen determinations was made as suggested by Kirshusing his values for the enbaum (4, densities of HzO and 100% DzO a t 25.00' C. DzO Analysis by Nuclear Magnetic Resonance, T h e N M R analysis of Table 1.
Results of D20 Analyses
Atom %D
Method Iron decompositionmass spectrometer 99 82 99 84 Density 99 84 NMR
Std. dev. atom
7 0 f-0 02 +0.02 f-0 01
the DzO was made with a Varian A-60 instrument. The procedure is similar to that of Goldman (3). Three successive additions of known amounts of HzO were made to the DzO. A plot of the integrated XMR signal us. added HzO was extrapolated to zero XMR signal to obtain the protium content of the original sample. RESULTS A N D DISCUSSION
Four runs each were made for the iron decomposition and density methods. One sample was analyzed by NhlR. The results are summarized in Table I. The accuracy of the iron decomposition - mass spectrometer method, when carried out with sufficient care, is thus confirmed by the agreement with other methods. An uncertainty of O.OOlyc in the density of pure DzO results in an uncertainty of 0.01% in the deuterium content. Densities reported (If) for 100% DzO show variations which could result in an uncertainty of 0.05 to 0.10% in a deuterium content based on density measurements. The NMR method for the measurement of small amounts of protium in deuterium oxide permits the deuterium content to be known to *O.Ol% in the present case, The excellent agreement with the density method substantiates the value of the density of 100% DyO used ( b ) , 1.10451 grams per ml. at 25.00' C. ACKNOWLEDGMENT
We thank D . P. Hollis of T'arian Associates for the NRIR analysis of the D20. LITERATURE CITED
(1) Bauer,
Weissberger, ed., "Physical Methods of Organic Chemistry," Chap. VI Interscience, ?Jew York, 1949. (2) Goldblatt, M., Los Alamos Scientific Laboratory, University of California, Los Alamos, 1;. M., unpublished data, 1962. ( 3 ) Goldman, M., Arch. Scz. (Geneva) 10, 247 (1957). ( 4 ) Kirshenbaum, I., "Physical Properties of Heavy Water," pp. 10-16, McGrawHill, Kew York, 1951. (5) Ibzd., p. 12. ( 6 ) Ibzd., p. 25. (7) Ibzd., p. 199. ( 8 ) Ibzd., p. 244. (9) Knowlton, J. W., Rossini, F. D., J . Res. S a i l . Bur. Std. 19, 605 (1937). (10) Lewis, G. K.>Cornish, R. E., J:,4m. Chem. SOC.5 5 , 2616 (1933). (11) Shatenshtein, A. I., et al., "Isotopic Water Analysis," A . E . C.-tr-4136, 1960; 2nd ed., 1957, p. 65. Available from the Office of Technical Services, Department of Commerce, Washington 25, D. C. MAXWELL GOLDBLATT W. M. JONES S . , A.
Los Alamos Scientific Laboratory of the
University of California
Los Alamos, N. M.
Work performed under the auspices of the U. S. Atomic Energy Commission.
