Anal. Chem. 1981, 53, 243-245
243
Vibrating Probe Density Meter for Determination of Atom Percent Deuterium in Lithium Hydride-Lithium Deuteride Mixtures L. A. Green," T. 1.Adams, and J. H. Hamilton Oak Ridge Y-72 Plant, P.O. Box Y, Oak Ridge, Tennessee 37830
Atom percent deuterium in llthlum hydrlde-llthium deuteride (LiH/LiD) mixtures are determlned from the denslty of a water-heavy water mixture obtalned by the decompositlon and oxidatlon of samples. The denslty Is measured by using a vibrating tube density meter which requlres no LIH/LID standards, only pure water and alr or other denslty standards. The samples are decomposed In a Leco Induction furnace, converted to the corresponding oxides, and condensed In a speclally deslgned cold trap fabricated for efflcient entrapment without contact with atmospherlc water vapor. A vlbratlng probe denslty meter determines the density of the waterheavy water mixture; the denslty Is proportlonal to the atom percent deuterlum in the LiH/LID sample. At the 95% confidence level, the atom percent dueterlum Is determined with a precision of less than 0.2% (relative standard deviation) for a single determination. By use of two Leco Induction furnaces and one vibrational probe density meter, 18 samples per 8-h shift can be analyzed.
Determination of atom percent deuterium in LiH/LiD mixtures using a mass spectrometer has proved to be difficult and time consuming. For achievement of increased accuracy and precision with reduced analysis time, a vibrating probe six-place density meter has been evaluated. The density determination is based on measuring the change in the period of oscillation of a vibrating U-shaped tube when the tube is filled with the decomposed and oxidized hydrogen isotopes of the sample. The following relationship exists between the period of oscillation 2' and the density p (1): p = A ( P - B)
(1)
A and B are instrument constants which are determined through calibration with fluids of known density. The major problems encountered in applying the density method to LiH/LiD mixtures were achieving complete sample decomposition, complete oxidation of the liberated hydrogen-deuterium gas mixture, complete entrapment of the water-heavy water mixture, and prevention of carry-over contamination from subsequent samples. Three control batches of LiH/LiD were formulated and analyzed for atom percent deuterium by mass spectrometry, nuclear magnetic resonance, and density meter. By use of the method described in this report, the data showed that the density method compared favorably with the other techniques. See Table I (2).
EXPERIMENTAL SECTION The hydrogen-deuterium isotopic ratio can be determined in lithium hydride-lithium deuteride mixtures by converting the hydrogen and deuterium to their corresponding oxides and finding the density of the resulting solution. A simple calculation will convert the density to atom percent deuterium. Care must be taken not to expose the water product to atmospheric water. 0003-2700/81/0353-0243$01 .OO/O
Apparatus. A Wallace and Tiernan absolute pressure gauge, Model 61A-ID-0800,measured room pressure. Four-inch nickel or steel combustion boats held the sample inside the Leco induction furnace. The furnace was modified to accept boats in the horizontal position. The vibrating probe density meter, Model DMA60/DMA601, equipped with a Hotpack water bath, was purchased from Mettler Instrument Co. The copper oxide conversion tube is described in Figure 1. The water trap is described in Figure 2. A digital thermometer with a fast response thermocouple was purchased from Bailey Instruments, Model No. BAT 8, for reading the vibrating probe chamber temperature. The rubber septa which fit on the water trap were purchased from Preiser Scientific, catalog number 10-4798,EPP #02. The syringe used to transfer water from the water trap to the density meter was purchased from Becton-Dickinson, catalog number 5623, ICC TB. Reagents. The tin used as an accelerator in the induction furnace was purchased from Leco Corp., catalog number 501-076. Procedure. The density meter must be calibrated daily due to changes in atmospheric pressure and temperature. The density meter and water bath must reach thermal equilibrium and vary no more than 0.1 "C at 25 "C. The sample cell is cleaned by injecting with deionized water, injecting with acetone, and airdrying with the air pump. After thermal equilibrium is reached, the density meter temperature and absolute atmospheric pressure are recorded along with the period of oscillation. The sample cell is then carefully filled with deionized water, and the period of oscillation for water recorded after thermal equilibrium is achieved. The sample cell is recleaned and the period for air is rechecked. A 1.5-2.0-g portion of the lithium hydride-lithium deuteride sample is weighed into a nickel boat, between layers of tin metal, and covered with aluminum foil. The reaction boat is inserted into the modified Leco furnace and a water trap is connected to the 850 "C copper oxide conversion tube (4). Ample time, usually 3 min, is allowed to purge the system. After the purge is complete, the water trap is immersed in a liquid-nitrogen Dewar. The furnace is powered to 6.5 mA for 4.5 min; this power setting is adequate for the sample to reach the 700 "C necessary for rapid sample decomposition. The collection bulb is sealed and removed from the Dewar, and the decomposed sample is removed from the tube furnace. See Figures 1-3. After melting, the period of oscillation for the sample, now converted to a water-heavy water mixture, is obtained in a manner similar to that used for the water standard.
RESULTS AND DISCUSSION In order to ensure that all hydrogen and deuterium in the samples were being converted to the water-heavy water and trapped, the percent recovery of the theoretical water-heavy water mixture formed was determined for 19 control samples (see Table 11). For calculation of the percent recovery of water-heavy water formed, an arrangement was made to weigh the water trap before and after sample entrapment. The three control samples used were analyzed and found to have approximately 3% impurities which were taken into account in calculating the theoretical water-heavy water. The average recovery of the 19 controls was 96.47% with an absolute limit of error of *3.94% at the 95% confidence level. Carry-over contamination (memory effect from one sample to the next) was checked by analyzing several samples low in 0 1981 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 53, NO. 2, FEBRUARY 1981
244
Table I. Precision and Accuracy of Control Batches Based on Control Batch Analysis (3) control batch no. 1 2 3 a
atom %D
- 6550 85
no. of samples 12 12 12
Mettler density meter mean, RSD, a atom % % 49.76 64.95 85.91
0.12 0.05 0.08
mass spectrometry ( 2 ) mean, RSD,= atom % % 49.86 65.24 85.54
0.36 0.38 0.35
NMR ( 2 ) mean, RSD,“ atom % % 49.42 65.13 85.64
0.99 0.71 0.39
Calculated at 95% confidence level. Table 11. Percent Recovery of Theoretical Water/Heavy Water Formed %
material control no. control no. control no. control no. control no. control no. control no. control no. control no.
recovery 1 1 1
1 1 1 1
1 1
93.23 97.08 97.51 98.07 97.39 95.60 95.79 98.18 97.13
%
material control control control control control
recovery
no. 2 no. 2 no. 2 no. 2 no, 2
control no. control no. control no, control no.
control no. 3
98.33 99.08 95.53 96.81 99.79 96.02 96.77 90.00 95.45 94.35
D
Table 111. Memory Effect Study of Samples of Different Concentrations
4L 8 m m Figure 1. Copper oxide conversion furnace: (A) wirawound ceramic heater: (B) quartz tube; (C) copper oxide; (D) quartz wool.
rerun sample low in deuterium content (atom % D) 0.0478 0.0203 0.0438 av 0.0373
of sample
sample high in deuterium content (atom % D) 85.826“ 85.860 av 85.843
low in deuterium content (atom % D) 0.1888 0.0536 0.0380
a Note that the first result is only 0.084 atom % lower than the average shown in Table I1 for the 85% atom D control batch. Note that the third analysis after the high-level deuterium sample showed very little or no “memory effect”.
V e n t and Seal Positions
Figure 2. Water trap: (A) Teflon stopcock: (B) Inlet: (C) balance h w (D) random indentations; (E) septum stopper.
deuterium content, then several samples high in deuterium content, and finally several samples low in deuterium content again. The results are given in Table 111. The maximum error that can result from the “memory effect” is approximately 0.2% absolute atom percent deuterium. Samples should be divided into three levels of deuterium content which are 10 atom % deuterium or less, 10-90 atom % deuterium, and greater than 90 atom % deuterium. Each sample should be decomposed and converted to its oxide on a furnace that has been conditioned for that level. Table I11 shows that conditioning consists of running at least two samples through the furnace and over the hot cupric oxide. The density of protium water (deuterium-free water at 25 “C with natural abundance of ISO) was calculated by assuming a linear relationship between the molecular weight of isotopes of water and their respective densities. The formula for calculation of protium oxide density (D,) from molecular weights is
U
Figure 3. System schematic: (A) copper oxide conversion furnace: (B) water trap; (C) Dewar: (D) modified Leco furnace; (E) helium supply.
where 18.015 05 = Mp = molecular weight of protium water (5),20.027 604 = Md = molecular weight of deuterium water (5, 6), 18.01534 = M, = molecular weight of natural water
Anal. Chem. 1981, 5 3 , 245-248
(5),1.104456 g/cm3 at 25 "C = Dd = density of deuterium oxide (7), and 0.9970429 g/cm3 at 25 "C = D, = density of pure natural water (7).From the above equation, the density of protium oxide is 0.997 027 4 g/cm3. The instrument constant "k" is calculated from (3) where TI = the period reading for pure natural water, Tz= the period reading for air, D, = the density of water at 25 "C (g/cm3), and D, = the density of air at 25 "C and ambient pressure (g/cm3). If the density of air is not known, it can be calculated from 0.0012930 P D, = (4) 1 (0.00367 X t)%
+
where D, = the density of air (g/cm3), t = temperature ("C) and P = pressure (torr). The density of the unknown sample (d,) is calculated as
+
d, = k(T2 - TW2) D,
(5)
where k = the instrument constant (eq 3), T, = the instrument reading for the unknown sample, T, = the instrument reading for pure natural water, and D, = the density of water at 25 "C. The atom percent deuterium oxide (N) is calculated from (8)
N =
D, - D, Dp((Md/Mp) - 1) +'Ds(1 - (MdDp/Mpd))
x 100 (6)
where at 25 "C D, = density of sample, D, = density of protium oxide, Dd = density of deuterium oxide, Mp = molecular weight of protium oxide, and h f d = molecular weight of deuterium oxide. Constants as of April, 1980, are D, = 0.997 027 4 g/cm3, Dd = 1.104456 g/cm3 (5),Mp = 18.01505 g/mol (6), and Md = 20.027604 g/mol (6, 7). The determination of deuterium in lithium hydride-lithium deuteride mixtures using the vibrating probe density meter is a useful analytical
245
technique. Comparing results with other methods of analyses has shown that the electronic density determination is more precise and less time consuming than mass spectrometry and nuclear magnetic resonance. The vibrating probe is more accurate than the other methods of analyses on a broad range of concentrations because there is no dependency upon empirical calibration with a "known" deuterium standard. High-purity natural water was used to calibrate the electronic density meter, but any precisely known density standard could have been used.
ACKNOWLEDGMENT The authors are grateful to R.L. Jamison, Jr., and J. W. Charles, Jr., for their help in locating and calculating the most recent values for constanta in the equations and to the Nuclear Magnetic Resonance Laboratory and the Isotopic Laboratory for their analyses of the samples. Thanks is given to the Materials Testing Laboratory for modification of the Leco induction furnace.
LITERATURE CITED (I) Mettler Instrument Corp. "Operating Instructions for Mettler Density Instrument DMA 60/601";Mettler Instrument Corp: Hightstown, NJ, 1977. (2) Johnson, E. E., Union Carbide Corp.-Nuclear Division, Oak Ridge Y12 Plant, Oak Ridge, TN; personal communication to L. A. Stephens, Sr., March 20, 1978. (3) Kohlraush, "Praktische Physiks"; G. G. Toebner; Stuttgart, Germany, 1968: Val. 3. Sectlon ~22. ........... (4) Furman. N. Horwell In "Scott's Standard Methods of Chemical Analyses", 5th ed.; Van Nostrand: New York, 1948;p 389. (5) Table of Isotopes "CRC Handbook of Chemistry and Physics", 58th ed.; Chemical Rubber Publishing Co.: Cleveland, OH, 1978; p 8271. (6) Pure Appl. Cbern. 1974,37,600. (7) Jones, Frank, National Bureau of Standards, Washington, DC, personal communication, Feb 1978. (8) Kirschenbaum, Isidor "Physical Propertles and Analysis of Heavy Water", National Nuclear Energy Series; McGraw-Hill: New York, 1951;p 15.
RECEIVED for review May 27,1980. Accepted November 12, 1980. The Oak Ridge Y-12 Plant is operated by the Union Carbide Corporation's Nuclear Divison for the Department of Energy under U.S.Government Contract W-7405-eng-26.
Radiotracer Techniques for Evaluation of Selenium Hydride Generation Systems D. C. Reamer,* Claude Veillon, and P. T. Tokousballdes' Human Nutrition Research Cenfer, USDA, Building 307, Room 2 15, Beltsville, Maryland 20705
Several SeH, systems and materials of constructlon are evaluated by use of '%e as a radiotracer. Polypropylene, two types of Teflon, and both silanired and unsllanlzed glass are evaluated. Glass and polypropylene exhibit the greatest absorption of selenium and silanired glass the least. A quartz furnace atomic absorption system Is described havlng a detection llmlt of 3 ng.
The utilization of hydride generation/atomic absorption spectrometry (AAS)for the analysis of selenium is continually Present address: 22 Narcissou Street, Kiffissia, Athens, Greece.
increasing in popularity (1-12). Siemer and Koteel (8)compared different hydride generation/AAS techniques and mentioned methods of optimizing systems to obtain maximum sensitivity. However, little information is available on the adsorptive effects of various construction materials for hydride generators. McDaniel et al. (5) used radiotracers to evaluate a variety of existing procedures for SeHz generation. With their system, it was reported that the SeHz was being transferred from the solution to the atomization source with an efficiency approaching 90%. The present paper describes radiotracer studies designed to investigate the performance of different types of materials used in the construction of SeHz generators. The evolution and transport of SeHz from the acid medium can be affected by the type of material used in
Thls article not subject to US. Copyright. Published 1981 by the American Chemical Society
