lect the metal on a tared filter paper (2cni. diameter), and \Tash nith hot water, 95% ethyl alcohol, and dicthyl ether. TVc4gh. mount, and count the isolated ruthcnium. RESULTS A N D DISCUSSION
Table I summarizes thc, rrsults of rutheniuni analyses of aqueous solutions of mixed fission products hy both thc, distillation method of Coryell and Sugarnian ( d ) and the mrthod described. The pi,ccision of the method is coniparable to that obtainc4 by the distillation method, + 3 to A%,. Tlic data in Table I illustrate the accuracy obtainable n-hen t,lie method described is carefully followed. The nietliocl is flexible, in that the rutlieniuni metal can easi]:. lie dissolved 11-ith potassium
periodate or sodium hypochlorite and a series of zirconium hydroxide scavenges can be made. Decontamination factors of the order of lo4 have been obtained froni the other major fission products and protactinium with the carrier yield about i&. The method describcd is suggested as another means of performing radiocheniical ruthenium analyses. even though the decontamination obtained and t,he analytical time required are not inigrovenients over the distillation t"hniquc. The method (n.ith modifications) has been routinel:. used to determine low concentrations of ruthenium activity in large water volunies. The oxidation of rutheniuni with potassiuni periodate in an alkaline niediuni and fixation n-ith sodium hypochlorite (8) are useful in decontaniination of glassware, and application as a lracliing agent for
fission ruthenium in sonie soils is being investigated. LITERATURE CITED
(1; Connick, R. E., Hurley, C. R., J . A m , Chem. SOC.74, 5012 (1952). ( 2 ) Coryell, C. L),>S u p m a n , S., ',Iiadiochemical Studies. i he Fission l'rodiicts," paper 260. 1). 1549, 1 I d ; r a w Hill, S e w York, 1951. ( 3 ) Gresky, A. T., L-, S. htoniic 1;iiergy Comm., Re;it. ORNL-614 (1950). ( 4 ) Hopkini, B. S., "Chapters i n the Chemistry of thc Less Yaniiliar Elements," 1-01.11, 11. 2;3! Stipe3 Pulilishing Co., Champaign, Ill.. 1939, ( 5 ) Marshall, E. D , , Itickard. It. R . , . % S A L . CHEM. 22, (1'350). ( 6 ) \lead, F. C., Jr., C . ti. .Itoiiiic Eriergy Comm., Rept. AECD-49 (1949). (T) [bid., MLM-30 (19491. ( 8 ) Stoner, G . -1.) .Is.LI, CHEII. 27, 1186 (1955).
RECEIVEDfor revien- J d y T , .iccepted October 9, 1958.
1038.
Determination of -Hydrogen in Alkali Metals by Isotope Dilution Method BEN D.
HOLT
Argonne National laboratory, lemont, 111
b The rapid exct,ange of hydrogen and deuterium in sodium or NaK affords a convenient method for hydrogen determination in these metals. Spikes equivalent to 5 to 250 p.p.m. of hydrogen have been recovered on 2gram samples with a standard deviation, from the quantity added, equivalent to * 2 p.p.m. An 8-inch borosilicate sampling tube serves as the reaction vessel and as the gas bulb for mass spectrometric analysis. With many such tubes on hand, samples can b e taken a t sites of industrial operations and transported to the laboratory for analysis. In the analysis of NaK it i s nec?ssary to apply a correction factor to compcnsatz for the effect of diffsrent rates of formation of the l-,ydrides and deutyrides in the cooler zon+s of the tub3 during equilibration. For sodium this e f f x t i s negligible and no correction i s necessary. The time required for analysis after the sample is taken is about 4 hour.
I
in liquid-metal-cooled reactors during the past decade has necessitated a good method for the determination of hydrogen in alkali metals and alloys. A few years ago Pepkowitz and Proud (6) reported a XTCREST
unique method by v, liich t,lie metal was heated to 700" (I. in a sealcd iron can and the resulting hj-drogen pressure surrounding the can in a Twuuiii system \vas taken as a measure of thc hydrogen content of the sample. Successful use of this niet,hod deniands conipl& liberat'ion of all the hj-drogrn from the sample into thc gaseous phase. Tests niadc a t this laboratorj- indicattd that liberation of hydrogen \I as not cwnplet,e. but n-as controlled by an apparrnt equilibrium bet w e n the liberated hjdrogc,n outside the can and thc heutcd sample inside the can. Willianis' study (8) of the sodium-hydrogen-ox>-gen sj-stem appears to lend support to this idea. The isotope dilution t,cchniquc ( I , 3: 4, 7 ) is not hindcred bj. such an equilibrium but is dependent upon it. Simpson and Kauh (6' p r o p o s d an isotopc dilution method in n.liich the metal was converted to osidcs by purified oxygen and equilibrat'cd ith dtwtoriuni oxide of Iinon.11 purity with rcspwt to hydrogen. By mass spectronietric analysis of the dcuterium oxidv distilled from the equilibrium solution, an rstimate could be madc of the hydrogrn contributed by the sample. Poor prccision was attributed to the very great difference in magnitude of the quantities of the two isotopes and to the accumulative contamination errms involved in the various
stcps of handling the deuteriuni osidc and the sample. A simplified iscitopc dilution nicthod for hydrogen in sodium and S a K is presented, which is similar to a teclinique used by Zaidei and Petrol. (9)for hydrogen in zinc. iron, and Xichrome. APPARATUS
Figure 1 s1ion.s the pi1)cttc.r used to delivcr a mcasi:rcd quantity of 99.5% pure deuteriuni into thc r;ampling tube. T o siniplif!~ calculations the same yiantity was taken for ever>- s a n i i ~ l (and ~ Iilank. The volunir of thc pipet' hulb was 21.39 cc.; the tcnipcrature was held constant by room air-conditioning; and the pressure W R S adjustc~don the open-well manonictcr. The 8-inch. borodicate sampling tube served as the equilibration vessel and as the gas 11~111~for niass spectrometric analysis. Its il(4ccator-type stopcock was fabricated from a 24, 25 standard taper joint. To Vac in Figure 1 refers to a vacuum line leading through a li !,uid nitrogen trap t,o a Duo-Seal mechanical pump. X tilting 11cLeod gage on this line was used to cheek the final pressurc in the sampling tubcls after evacuation. A 4-inch Hevi-Duty electric tube furnace was used to heat the tubes for ecuilibration of the isotopes. Set vertically on a firebrick base, and lined with brass pipe 1 inch in inside diameter, the furnace held the tube in an VOL. 31, NO. 1, JANUARY 1959
51
upright position at a suitably uniform temperature. The bottom support of the tube was such that the sample was located in the middle of the furnace, the temperature of which was indicated by a thermocouple. The mass spectrometer was Model 21-620 of Consolidated Engineering Gorp., Pasadena, Calif.
Deuterium Reservoir
Figure 1. Deuterium pipetter
24
SEY
RECOMMENDED PROCEDURE
A group of cleaned sample tubcs are disjointed and baked for 0.5 hour a t 520" C. in a muffle furnace to free them of adsorbed moisture. While still warm, each stopcock cap is replaced on its corresponding tube; and, with minimum exposure of the interior t o atmospheric moisture, the stopcock joint is greased and closed. One or two tubes of each group are selected to serve as blanks. After weighing on a triple-beam balance t o tvio decimal places, each tube is evacuated and transferred to the site of sampling. Tn-0-gram samples are placed in the tubes inside a gloved box filled with an inert gas that is free of water vapor and oxygen. These samples are taken directly from the system of interest at the operating temperature. They are allowed to cool quickly to room temperature to minimize possible loss of dissociating hydride hydrogen during sample cooling. The tubes are reweighed on the same triple-beam balance and the gain in weight is taken as the weight of the sample plus the difference in weights of air and the gas in the gloved box. Each tube is evacuated on the pipetting apparatus (Figure 1) and, with stopcock S T remaining open, Sz is rotated to evacuate the deuterium line. The index of the meter stick scale is adjusted to the top of the mercury column and the capillary C-tube is immersed in liquid nitrogen. SIis closed and S4 is opened enough to admit deuterium to the pipet bulb in slight excess of 200 mm. of mercury pressure. With S4 closed, the pressure is adjusted to the exactly 200 mm. by means of SI, plug of which is grooved to afford precise control. S p is rotated 180' so that the deuterium confined in the bulb a t the observed pressure, volume, and temperature is expanded into the sample tube. Barometric pressure is used to push the mercury from the reservoir below, up through the bulb to stopcock S T . K i t h all the deuterium confined to the sample tube, the latter is rotated to close S T . The mercury is returned to the reservoir and the sampling tube is removed. To equilibrate the deuterium with sample hydrogen, whether present as hydroxide, hydride, or dissolved hydrogen, each tube is heated in the tube furnace for 5 minutes. It is then removed; cooled to room temperature; and flamed a t its midsection for about 0.5 minute with a Fisher burner to decompose the hydrides and deuterides deposited during the brief equilibration period. After cooling again, i t is attached to the mass spectrometer and the outputs at mass numbers 2, 3, and 4 are recorded.
52
ANALYTICAL CHEMISTRY
M e t e r Stick
-
-
Open W e l l Monometer 1.5mm. C a p i l l a r y
Mercury Reservoirs
P.p.m. of H
=
Table 1.
Hydrogen in Liquid Sodium, 1 10" C., Analyzed by Prescribed Procedure Hydrogen, y Spike ReDevi-
Material
SaHCOa
Added
covered
ation
15 127 103
13 125 105
-2 -2 +2
123
+5
107 118
115 106
106
118 103
Std. dev.
-1
f 3 -3 f 3
The H/D ratio is calculated from the net outputs ( 2 ) , (3), and (4) and the , and respective sensitivities, S H ~SED, SD~ of , the three gases involved:
where (2) = (total output of 2-peak)(outputs attributed to Dz and HD patterns). From this ratio the hydrogen concentration in the sample, on a veight basis, may be calculated as follows: P.p.m. of H = I(H/D)a (d)a - (H/D)b(d)bI (1.008) grams of sample where the subscripts refer t o data for sample and blank, and d is the number of micromole atoms of deuterium introduced into the tube. Because this number is adjusted to the same value for both sample and blank, the calculation is simplified to:
EXPERIMENTAL RESULTS
Table I shows results obtained on hydrogen-spiked sodium samples b y the above procedure. The standard deviation from the quantity added was *3 y of hydrogen, which, on the basis of 2gram samples, corresponded to less than rt2 p.p.m. These samples m r e prepared by placing in the sampling tubes weighed amounts of spiking material before evacuation and sodium addition. The sodium, taken from a reservoir maintained at 110' C., was liquid and contained 4 f 2 p.p.m. of hydrogen, as determined b y this method on 12 unspiked samples. I n applying the method to NaK (22y0 Na, 78% K), the recovery of spikes was always incomplete. (The term "recovery" is used to compare quantities of hydrogen added with those measured by this method. It does not imply isolation of the element sought, for such is not involved in isotope dilution techniques.) This may have been caused b y a difference in reaction rates of the two isotopes with freshly condensed alkali metals in a zone of the tube where the temperature gradient was optimum for hydride and deuteride formation. This formation was evidenced b y a decline in sample tube pressure with heating time, and by the appearance of microscopic crustlike deposits on the shiny, freshly condensed metal globules.
I
20
I
I
I
I
I
-
01 0
I
I
I
I
10 20 30 40 M I N U T E S OF H E A T I N G
I
1
50
Figure 2. Sample tube pressure vs. time of heating for isotope equilibration
A plot of tube pressures us. heating time is shown in Figure 2. If the hydride had formed at a greater rate than the deuteride, the H D ratio of the remaining equilibrium mixture should have decreased with time also. This was found to be true, and to account for a decline of per cent recovery with increase of heating time on a group of spiked samples (curve B , Figure 3). When the cause of these lo^ recoveries became evident, and the tubes were flamed, most of the combined hydrogen and deuterium were returned to the gaseous mixture with a sudden increase in pressure and, to a lesser degree, a n increase in H/D ratio. This dehydriding treatment raised the recovery level from 85 to 92%. Table I1 shows some of these comparative results. Inasmuch as some hydrides and deuterides are doubtless reformed in adjacent cooler zones of the tubc even during the flame treatment, complete estimation of hydrogen in S a K n ithout a correction factor may be approached but perhaps not attained. I n the case of sodium, the corresponding effect )vas apparently too small to be of significance. Curve A , Figure 3, s h o m not only the improred recoveries of hydrogen in K a K due to the dehydriding treatment but also the lack of a decline with time as in
B. This indicates t h a t a n y heating period in the range of about 4 to 12 minutes may be selected for the equilibration. Longer periods are unnecessary and even objectionable when carbon compounds are present, such as sodium bicarbonate or calcium oxalate monohydrate used in this viork as hydrogen spikes. K h e n such compounds \yere present, the mass spectrum shelved increasing concentrations of the mixed methanes of hydrogen and deuterium as the heating time was prolonged. Analyses of these mixtures based on the spectra of a set of standard methanesCHI. CHsD, CH2D2,CHD8. and CDIrevealed t h a t the H / D ratio in the methanes was identical to that of the mixture of H2,H D , and D,. The H/D ratio of the latter mixture therefore could be taken as the uncorrected ratio of the entire system. However, after the hydrogen-rich hydride-deuteride mixture was decomposed, the H/D ratio taken from a n analysis of the H2, H D , and D2, neglecting the methanes, was higher than the true ratio of the entire system. The effect is demonstrated by the abnormally high value in curve A , Figure 3. It was concluded, therefore, that when such carbon compounds are present, it is better to terminate the heating period before significant amounts of methanes are produced. I n the temperature range between 450' and 530" C. no one value stood out as optimum for best recoveries; but inasmuch as the higher temperatures entailed somewhat higher tube blanks, the lower value of 460' m s adopted. One attempt was made to use solid sodium hydroxide as the spiking material in a set of seven sodium samples, but a suitable technique for weighing out the material on a microbalance without moisture contamination was not perfected. The results were high by about 50 y of hydrogen on spikes ranging from 94 to 924 y of added hydrogen. Hoivever, one specially prepared set of sodium bicarbonate-spiked samples was
Table II. Hydrogen Samples Equilibrated 15 Minutes at 520' C. No Dehydriding Treatment Spike Hydrogen, y material Added Recovered X 1/0.85 Deviation SaHCO3 97 8T 102 +5 141 125 14i +6 252 210 24T -5 309 252 296 - 13 594 506 595 +1 CnCzOi H,O
36 143 23 1
31 112 206
36 0 132 -11 242 +11 Std. dev. 1 8
IO0
. I d
A
> c
80
W
>
0
o
60
W K
5
40
w
0
E~
20
a -
0
0
IO 20 30 40 M I N U T E S OF H E A T I N G
50
Figure 3. Per cent recovery of hydrogen in NaK vs. heating time A. B.
With dehydriding treatment Without
considered to be a good substitute for sodium hydroxide because in this case the poTvder was weighed into small glass capsules which n-ere placed within the sample tubes in such a manner as to keep the bicarbonate out of contact with the alkali until the heating was begun. Presumably the sodium bicarbonate thermally decomposed, releasing water, which reacted with the metal to give the hydroxide and hydrogen. Recoveries on these were comparable to other sodium bicarbonate spikes unisolated by capsules. The blank, as urjed in the procedure, accounts for hydrogen impurity present in the deuterium before equilibration; and i t serves as a monitor of moisture contamination xhich would s h o x up in peaks 17, 18, 19, and 20. A more comprehensive blank v ould include the hydrogen which might be liberated by the chemical reactions of the alkali metal with absorbed moisture and with the glass of the sample tube. Such a blank was determined by an analysis of a series of sodium samples varying in weight from 1 to 6 grams. A plot of measured hydrogen us. sample weight gave a straight line. I n a n extrap-
Recovery in NaK
Samples Equilibrated 5 Minutes at 460" C. Flamed Tubes t o Decompose Condensed Hydrides Spike Hydrogen, y material Added Recovered X I /0.92 Deviation SaHC03 11 15 16 +5 31 31 34 +3 68 i4 -1 It3 88 84 91 +3 116 10; 116 0 225 208 226 +1 -5 403 366 398
--
1 3
Or 1 2 p.p.m. on 2-gram samples
VOL. 31, NO. 1, JANUARY 1959
53
olation to zero weight the intercept is the total blank, including the effect of the glass attack. This value was not significantlv higher than t'he blank referred t o abore; thus it !vas concluded that the effect the gla" att'ack "as nil. ACKNOWLEDGMENT
The author wishes to thank A. D. Kirshenbauni and D. D. Killiams for
their helpful suggestions in review of this paper. LITERATURE CITED
Goris~ p., DuffY, E., TirWY, F. H., ANAL.CHEJI.29, 1590 (195T). (2) Holt, €3. D., E.S. Atomic Energy Comm., Rept. ANL-4388 (1950). (3) Kirshenhaum, il. I)., Grosse, A. V., Ax.4~.CHEJI. 26, 1955 (1954). (4) Kirshenbaum, -1.D.: Grosse, A. \-,, d n a l . Chim. Acta 16, 225 (1957). (5) Peplrowitz, L. P., Proud, E. R., 1x11. ESG.CHEX., AX'AL. ED. 2 1 , 1000 (1949).
(6) Simpson, 0 . C., Rauh, E. G., C. S. Atomic Energy Comm., Rept. CF-3748 (1946). ( i ) Tilton, G. R., Aldrich, L. T., Inghiam, M. G., Asar,. CHEX 26, 894 (1951). (8) \Yiiliams, I). D., S a v a l Research Laboratory, Memorandum Rept. 33 (1952). (9) Zaidei, A , y , , Petrov, -1,A,! Zhur. Tekh. Fir. 2 5 , 2571 (1955).
RECEIVEDfor reviev April 28, 1958. Accepted September 18, 1958, Based on work performed under the auspices of the U.S.iltomic Energy Commission.
Radiometric Determination of Krypton-85 R. B. REGIER Atomic Energy Division, Phillips Petroleum Co., Idaho Falls, Idaho
,Apparatus and procedure for the determination of krypton-85 in gas samples are described. With a single dilution, samples ranging in specific microactivity from about 1 X curie to 10 millicuries per ml. have been analyzed. The method of determining the absolute disintegration rate of krypton-85 is outlined. In routine use, the procedure i s precise to 7.1y0 a t the 95% level of confidence. The accuracy has been estimated b y comparing the analyses of high activity samples with those obtained with a mass spectrometer. In the comparison of 1 1 such samples, the average of the radiometric to mass ratios was 1 .O 1 f 0.105 a t the 95% confidence level.
lop3
R
measurements of gaseous activity are frequentlj. made by introducing the sample directly into the smsitive volume of the counter, so t'hat it is an integral part of the counter filling gas ( 2 , 3 ) . This procedure is slon- becausr the plat,eau of the counter must be measured with each filling. components of the gaseous sample not compatible with a good filling gas must be removed prior to analysis, and the maximum activity that can be tolerated in a sample is fairly lo^. A method has been developed that obviates thew disadvantages, and is both rapid and accurate over a vide range of activities. -4DIOMETRIC
APPARATUS
Figure 1 depicts the vacuum line used t o make sample dilutions and to fill the cell which contains the gas for beta counting. Pressures were measured with a Todd Universal vacuum gage, A , a NcLeod-type gage, which has three 54
ANALYTICAL CHEMISTRY
pressure scales: 0 to 0.5, 0 to 5, and 0 t o 25 nini. of mercury. The counting cell filler, B , was connected to the vacuum line with an 1 8 j i spherical joint. This filler n-as made froni a pair of standard-taper 55, '50 joints, 15-ith a three-way, 3-mm. T-bore stopcock. A female standard-taper 5,'12 joint inside thc filler supported the gascounting cell. The gas-counting cell n'as machined from brass. It was 1 inch in diameter by '/4 inch deep (inside diniensions), and its wall thickness was ' j Sinch. A Mylar nindow 1.8 mg. per sq. em. was ceinent'ed to the top of the cell n-it'h Multi Lok adhesive (Sational Starch Products, Inc.). An int'cgral part of the cell was a ':,-inch long tube Ivhich extended beneath the cell, and into which a 7320 Corning microstopcock was cemented with Apieson W v-ax. The other arm of the stopcock was attached to a male standard-taper 5,"12 joint. The over-all length of the counting cells, 6.7 to 7.0 cm., permitted use under an end-nindow proportional bet'a counter. The hole in the base of the brass cell was 0.0625 inch in diameter, small enough so that
t,he gas in the stem of the cell contributed insignificantly to the counting rate. Sample gas was adiiiit'ted to the vacuum line through stopcock 7, rvhich had a three-way T-bore plug, permitting the sample line to communicate with both t,ube D and the rest of the Tube D, connected through sto \\-ith a' Irveling bulb containing mercur!-. was used to regulate the volume of sample admitted to the systriii. Initially, D had a volume of about 125 nil., so that by appropriate manipulation of the lcveling bulb and the stopcocks, saniples could be pumped from t'he sample container into bhe vacuum line. Subsequent,ly, this \vas found unnecessary, and a 20-mm. tube about 3 inches long was substituted. Tube C was a condenser ininiersed in liquid nitrogen during portions of the sample preparation. Stopcock 5 was conncctcd u i t h plastic tubing t o a cylinder of compressed et'hylene. The IT-tube manometer, E , was filled with mercury. Rubber tubing connections )yere used b e t m e n stopcocks 6 and 7 , and hrtneen stopcock 7 and the w n p l e
Figure 1. Vacuum line for preparing krypton-85 samples
