Even though the copper and iron complexes with diethylacetic acid are extracted in solvents such as ethers, esters, alcohols, benzene, and halogenated hydrocarbons, diethylacetic acid was selected as the best solvent for this determination, since it absorbs below 390 mp and the excess reagent is extracted by the other solvents. This method of andysis is accurate and rapid for the determination of iron. I t is quite convenient since no prelim-
inary separations are necessary. The method was tested by analyzing h’ational Bureau of Standards Samples. For the 157a sample, the relative error of the average of the values obtained is 1.2701,. The 671 No. 1 sample is in complete agreement with the NBS recommended value. The sensitivity, defined as the concentration of iron in diethylacetic acid needed to produce a change in absorbance of 0.005, is 0.15 pg. per ml.
LITE~ATURE CITE^
(1) Am. Soc. Testing Materials, Phila-
delphia, “ASTM Methods for Chemical Analysis of Metals.” pp. 239-40, 1950. ( 2 ) Kraus, K. A., Nelson, F., “Geneva International Conference on Peaceful Uses of Atomic Energy,” Vol. 7 , Paper 837, United Sations, N. Y., 1955. (3) Ralph, W. D., Jr., Sweet, T. R., Mencis, I., ANAL.CHEM.34, 92 (1962). ( 4 ) Sporek, K. F., Ibzd., 33, 764 (1961). RECEIVED for review March 19, 1963. Accepted August 16, 1963.
Determinaition of Hydrogen in Sodium by Isotopic Dilution with Tritium CLAYTON EVANS and JOHN HERRINGTON United Kingdom Atomic Energy Authority, Aldermaston, England
b Isotopic dilution with tritium i s an efficient method for determining hydrogen in sodium. Satisfactory recoveries were obtained using hydrogen spikes of 16 to 90 PI., corresponding to 140 to 4000 p.p.m. of hydrogen in sodium. The recovery has been shown to b e independent of concentration. Equilibrium between the added tritiated-hydi*ogen and the hydrogen in the snmple was established b y heating in a sealed borosilicate glass t h e a t 420” C. for 10 minutes. The’ activity of the tritiated hydrogen scimples was determined b y Geiger counting.
E
with the liquid metalssodium and sodi Im-potassium alloy-as coolants in reactors has shown that strict control of impurities is essential. Hydrogen is one of the most troublesome, since it not only causes embrittlement of thr fuel element cans, but also precipitates as alkali hydrides, thereby causing plugging of the cooling circuits. A satisfactory method for the determination of hydrogen in these metals is therefore necessary. Ilolt (4) has discussed various methods of analysis and reported an isotopic dilution technique with deuterium employing mass spectrometry for the analysis of hydrogen-deuterium mixtures. We have shown that deuterium and mass spectrometry can be replaced successfully by tritium and Geiger counting. By using “break-seals ’ instead of taps, it was possible to imrrerse the ampoule completely in the furn:tce while carrying out the equilibration. This design prevented the sodium from distilling out of the heated zone and recombining with the hydrogen on condmsing on the unheated portion of the apparatus as deXPERIENCE
scribed by Holt (4). The equilibration ampoules mere inexpensive and were discarded after the experiment. EXPERIMENTAL
Apparatus and Procedure. The apparatus is shown in Figures 1 to 5 . The ampoule used in these experiments is shown in Figure 1. It was made from 10-mm. diameter borosilicate glass tubing, the effective length of which was 17 to 18 cni. After degreasing, cleaning, and removing the stopcock, i t was baked a t 180-200” C. for ‘ / a hour. While still warm, the greased stopcock key was replaced and the tube closed with a stopcock and B14 cone covered with a Teflon sleeve. The ampoule was evacuated and weighed on a balance having a sensitivity of 0.2 mg. It mas filled with dry argon via the 3-mm. tap, then with the gas flowing through the ampoule and the dispenser, the ampoule was attached to the dispenser and the system evacuated. Khen Ioading samples from a large stock of commercial metal in an argon-filled glove box, a modified ampoule was used. The boat and pusher were discarded and the l314 socket sealed to the end instead of the side as in these experiments.
The dispenser was loaded either with commercial grade or hydrogen-free sodium and filled with dry argon. When using commercial grade metal, the descaled lumps were inserted through the U19 socket while a stream of dry argon flowed through the apparatus. The E19 cone and tap were replaced, the argon flow stopped, and the tap closed. The metal was melted and by manipulating the taps to the argon supply and vacuum pumps the liquid metal was filtered through the sintered glass disk. When hydrogenfree metal was needed, the B19 socket was removed and a subsidiary, allglass, multiple-stage distillation system sealed to the top of the dispenser. The metal was vacuum distilled into the dispenser and filtered through the glass disk. The distillation system was then sealed off and removed. Samples of sodium were dispensed into the boat by melting the stock of sodium, and lifting the ball-bearing with a magnet. The sample was allowed to cool and then the boat was transferred to the break-seal end by means of the magnetically-operated pusher, the pusher then being returned to its original position. The ampoule was sealed off a t A (Figure 11, and the remainder of the original ampoule was
-814
SOCKET
-
PUSHER
BOROSILICATE BOAT
Figure 1. Sodium sample tube - a m
s 10
BORE
H V TAP
CONE
VOL. 35, NO. 12, NOVEMBER 1963
1907
P
3
0 I ? CONE 4ND SOCKET
SINTERED GLASS FILTER DISC
SODIUM
,DIAMETER STEEL 0Aii
B 14 EXTEKDED CONE
Figure 2.
preset a t 420' C., raised until the ampoule waa completely immersed, and a cover plate fit,ted. The 100-ml. sampling bulb was connected via the two-way 4-mm. bore stopcock 2 to the ampoule and the system isolated from the vacuum pumps. The ampoule was heated for the requisite period; then, without removing the furnace the glass seal was broken and the gas phase expanded into the 100-ml. bulb (which was isolated) without delay by closing 2. The sample of diluted tritiated hydrogen thus obtained was transferred from the bulb into the small gas sample tube and this was sealed off a t Y (Figure 4) and attached to the counting apparatus (Figure 5). The gas was purified by diffusion through a palladium tube a t 600" C. before the specific activity was determined. The diffusion was assisted by a diffusion pump, which was later used to circulate the sample to overcome any fractionation which may have occurred during the passage through the palladium. The procedure for determining the specific activities of the stock and diluted tritiated hydrogen has been described (1).
Sodium dispenser
TPJTIATED HYDROGEN
HYDROGEN
PU 3
STANDARD VOLUME
Figure 3.
MACLEOD GAUGE
Gas dispensing apparatus
DISCUSSION
removed from the dispenser. The grease was removed from the B14 socket and the small tap and Tefloncovered B14 cone replaced. This section was evacuated and reweighed together with the section containing the sodium. The section containing the sodium was attached to the gas pipet (Figure 3) via the B10 cone. By means of the gas pipet (Figure 3) tritiated hydrogen and, when needed, natural hydrogen was measured into the ampoule. The natural hydrogen was stored on pyrophoric uranium (PU 3) from which it was liberated by heating. The stock of tritiated hydrogen was interchangeable between this apparatus and that used for counting (Figure 5). The main stock of tritiated hydrogen was stored on pyrophoric uranium (PU 1) and a subsidiary calibrated stock (2 X lo6d.p.m. per ml.) in the 250-ml. bulb, which had a heated side-arm; by this means the stock could be thoroughly mixed to overcome any fractionation which occurred on releasing it from the pyrophoric uranium (6). The pressure of the gas in the bulb of known volume was measured by the MacLeod gauge. After the gases had been transferred to the ampoule by raising the mercury in the pipet to the constriction near B, it was sealed off a t B (Figure 3). The ampoule thus loaded with sodium, tritiated hydrogen, and, when needed, natural hydrogen gas, was sealed on to the equilibration apparatus (Figure 4) a t X . The ampoule and cold trap were attached to the rest of the apparatus (Figure 4) via a B14 cone and socket. The section between X and the B14 joint was used repeatedly; a new ampoule was needed for each experiment. The apparatus was thoroughly degassed and the furnace, 1908
ANALYTICAL CHEMISTRY
Holt (4),when checking his technique, used either calcium oxalate monohydrate or sodium bicarbonate as a source of hydrogen for spiking the sodium. Hydrogen in sodium may be present in any or all of the following forms: dissolved hydrogen, or held as NaH, HCOB-, or HzO (mainly on the surface but partly dissolved or dispersed). However, a t 400' C. in the presence of excess sodium, the following reactions occur:
+ HZ 3000 c 2 Na + NaOH 4 NazO + NaH (6) 2 Na
+ 2H20 -+
2NaOH
The equilibrium pressure of hydrogen in the reaction 2Na
+ Ht s 2 NaH
is one atmosphere a t 420' C. (3). Therefore, since the equilibration between the added tritiated hydrogen and the hydrogen in the sample is carried out a t 420' C., hydrogen in any of the above forms is suitable as spiking material. Since hydrogen gas is the easiest to handle and measure accurately, it was used in these experiments. To check the accuracy of a method, it is normal practice either to compare results with those obtained by an established technique or to carry out recovery experiments on known additions. In the first case, a satisfactory technique was not available, so the alternative route was adopted. Incorrect results
for recovery experiments by the isotopic dilution procedure will be obtained only if isotopic fractionation occurs between the phases. This could occur if the solubilities of hydrogen and tritium or the stabilities of their sodium compounds were sufficiently different a t the equilibration temperature. When using this technique for the determination of hydrogen in metals, it is first necessary to determine the time a t a suitable temperature needed to establish equilibrium between the added isotope and the one to be determined. The work of Holt (4) demonstrated that a heating period of 5 minutes a t 460' C. was needed to establish equilibrium. Since we proposed to use a different handling technique, and to replace deuterium by tritium, these conditions had to be checked. In these experiments the equilibrium was carried out in sealed tubes, and consequently it was not possible to sample the gas phase at intervals while the reaction proceeded, as had been done when using solid samples (1). Therefore, to follow the exchange reaction it was necessary to repeat the experiment several times, using approximately equal amounts of sodium from one stock of metal, and to vary the heating period. However, before results of these experiments could be calculated it was necessary t o determine the apparatus blank. Determination of Apparatus Blank. For the experiments performed t o determine the equilibration time, only an approximate value of the apparatus blank was needed. Since hydrogen-
n
T O YACUUM
TRITIATED HYDROOEN
c
Figure 4. Hydrogen determination and counting apparatus
Figure 5. Equilibration sampling apparatus
and
gas
Table 1. Blank with Sodium (Commercial Grade) Present
free sodium was not available a t that time, i t was thoughl, that this could be obtained by using varying amounts of commercial sodium, determining the total hydrogen using a heating period of 10 minutes, and hack-extrapolating to zero weight of sod um. Working in an argon-filled glove box, the crust was removed from a lump of commercialgrade sodium and samples of varying size removed with a cork borer and scalpel. These samples were loaded into the equilibrium t u b s The results obtained are given in Table I. A large scatter in the values resulted and it was impossible to fit them graphically to a straight line. A niimerical analysis using the method of least squares gave a value for the blank of 0.02 ml. of Hz. The scatter of the values show that it is impossible to use small samples and that great care must be taken to remove completely the oui,er crust when analyzing commerc: al-grade metal. However, using this approximate value for the blank, we were able to proceed to the determination of the equilibrium time. When hydrogen-free sodium became available the blank determinations were repeated, and the results are given in Table 11. In the range 0.07 to 0.322 gram of Ne, the hydrogen found (0.020 ml. and a standard deviation of iO.006) was independent of the weight of metal used, and this was taken as the blank value. Contrary to the findings of Holt (4, the blanks obtained were significantly higher than those obtained in some experiments F erformed without sodium present (0.014 ml. and a standard deviation of i0.008:, indicating that hydrogen is liberate1 by the attack of sodium on the glass. The discrepancy between the results obtained by Holt (4)
and ourselves may be due to the difference in the pretreatment of the glass ampoules used for the equilibration. I n the present work, a high vacuum stopcock was attached, and, as it was not considered advisable to bake them a t a temperature approaching the softening point, a temperature of 180" to 200" C. was used instead of the 500' C. used by Holt. Determination of Equilibration Time. For these experiments a stock of metal was required in which all the possible hydrogen-containing impurities were present and uniformly distributed. Commercial-grade metal contains all these impurities but not uniformly distributed. Consequently this material was used, the blocks were melted on the sintered glass disk in the dispenser (Figure 2), and held at the melting point for a few minutes to allow the dissolved impurities to become uniformly distributed. The liquid phase was filtered into the lower section leaving the dross on the disk. Approximately 0.3 gram from this stock was used in each of the equilibration experiments. After adding a
Equilibration carried out at 420" C. for 10 minutea Sodium, gram HI found, ml. 0.032 0.018
0.006 0.020 0.022 0.080 0.107 0.160 0.289 0.346
0.014
0.020 0.028 0.014 0.040 0.033
Table 11. Repeat Blank Using Hydrogen-Free Sodium
Sodium, gram
Hr found, ml.
0.074 0.082 0.110 0.322
0.022 0.013 0.028 0.018
Mean blank and standard deviation =
0.020 =t0.006 ml./gram.
measured quantity of tritiated hydrogen, the samples were heated at 420" C. for periods varying from 3 to 15 minutes. The hydrogen determined after the various heating periods was calculated after applying a blank correction of 0.02 ml. of Hz. This blank correction (0.02 ml.) corresponded to a heating
bration curve
VOL 35, NO. 12, NOVEMBER 1963
1909
RESULTS
Table 111.
Recovery of Hydrogen Spikes
Hydrogen, ml. (S.T.P.) ReSodium, Total covery, % gram Added founda 0.294 0.465 0.463 100 0.129 0.302 0.316 105 0.121 0.389 0.401 103 0.170 0 550 0.536 97 0.109 0.565 0.603 107 0.340 97 0.056 0.349 0.021 0.177 0.1iO 96 0.020 0.492 0.496 101 0.254 100 0.010 0.254 0.020 0.649 0.653 101 0.027 1.020 1.031 101 0.793 99 0.021 0.799 Corrected for blank of 0.020 ml. 5
period of 10 minutes, and for periods less than this it may have been an overcorrection. However, by neglecting the blank completely, it was possible to show that equilibrium was not attained a t 3 minutes and that not less than 5 minutes heating at 420’ C. was needed to establish equilibrium. Consequently a heating period of 10 minutes at 420’ C. was adapted for all further experiments.
The results of the recovery experiments are given in Table 111. The volume of hydrogen in the sample was calculated from the usual formula: V = Vo(al/ai - 1) - b where V , VO,and b are the volumes of hydrogen in sample, tritiated hydrogen introduced into the ampoule, and apparatus bIank, respectiveIy; al and a2 are the initial and final specific activities of the tritiated hydrogen, The satisfactory agreement between the volumes of hydrogen recovered as determined by this technique with those initially added show that little, if any, isotopic fractionation occurs during the equilibration and gas phase sampling processes. The mean and standard deviation of the recovery experiments was 101 =t 3%. From Table I1 it is seen that the blank was 0.020 ml. and the standard deviation of a single determination was +0.006 ml. Consequently, it is possible to determine 0.040 nil. of hydrogen with a relative error of 1591,. Therefore, if sufficient care is taken when sampling the metal it is possible, using 2-gram samples, to determine the hydrogen in
metal down to the Bp.p.m. level with a relative error of approximately 15%. The experiments on the determination of the equilibration time showed that the temperature could be reduced from the 460’ C., recommended by Holt, to 420’ C. without exceeding the heating period of 4 to 12 minutes, which he found to be satisfactory. The possibility of using an even lower equilibration temperature and possibly reducing the apparatus blank without significantly increasing the time was not investigated. LITERATURE CITED
(1) Evans, C. Herrington, J., Proceedings of Internadional Atomic Energy Conference on the Use of Radioisotopes in the Physical Sciences and Industry, Copenhagen, Paper R.I.C.C. 39, September 1960. (2) “Handbook of Chemistry and Physica,” Chemical Rubber Publishing Co., Cleveland, Ohio, 1958-59. (3) Herold, A., Compt. Rend. 228, 686-8 (1949). (4) Holt, B. D., ANAL. CHEM.31, 51 (19.59).
(51 Wilhams, D. D. et al., U. S. National Research Lab. Memo No. 424 (1955). (6) Wilson, E. J., Evans, C.,U. K. A.E.A. Harwell Report I/M 31, 1954.
RECEIVED for review December 12, 1062. Accepted July 18, 1963.
Fluorometric Determination of Tungsten with FIavanoI RUDOLPH
S. BOTTEI
and
B.
AMBROSE TRUSK’
Department of Chemistry and the Radiation laboratory, University o f Nofre Dame, Notre Dame, Ind.
b Flavonol produces a blue fluorescence with tungstate ion in the p H range 2.5 to 5.5. The curve of fluorescence intensity vs. tungstate concentration is linear between the limits of 6 to 42 pg. of W in 100 mi. of solution. Vanadium, iron, and chrcmium interfere, even in small concentrations, while larger amounts of nickel, cobalt, manganese, and copper can b e tolerated. Other variables have been studied and are reported. A procedure is presented for the analysis of Ni-W alloys. Results b y this method are in excellent agreement with those b y other existing methods.
T
standard method for the quantitative determination of tungsten is a tedious, gravimetric procedure which has not been changed appreciably since 1895 (3, 6). Dams and Hoste (4) have shown that a t least 0.1% of the tungsten is lost in this method. Various volumetric, colorimetric, solvent extraction, and precipita1 Brother I. Ambrose Trusk, F.S.C. HE ACCEPTED
1910
ANALYTICAL CHEMISTRY
tion methods, as Fell as various combinations of these, have been proposed. The authors found no record to date of any fluorometric procedure for the quantitative determination of tungsten. In their fluorometric study of the zirconium-flavanol system, Alford, Shapiro, and White ( I ) observed that while zirconium and several other metals gave a fluorescence in acid solution with flavanol, only tungsten, of the 53 ions studied, gave a fluorescence in neutral solution. This paper concerns a study of the fluorescence of the tungstate-Aavanol system and the application of that fluorescence t o the analysis of Xi-147 alloys. EXPERIMENTAL
Apparatus. Fluorescence intensity measurements were made with a Turner manual fluorometer, Model 110. A Corning filter, CS 7-60, was used as a primary filter and a combination of a Wratten CS 2A and a Corning CS 5-61 as secondary filter. The fluorescence spectra were obtained with a Beckman Model DC
spectrophotometer equipped with a Beckman 73500 fluorescence attachment. Reagents. STANDARD TUNGSTATE SOLUTION. A standard solution was prepared by dissolving 2.6779 grams of Na2WOd.2H20 (Baker Chemical, Lot 1532, assayed a t 99.8%) in 1 liter of water. Gravimetric analyses (6) confirmed the concentration to be 0.008100M, or 1.4893 grams of W per liter. This was diluted, 10 ml. to 1 liter, to prepare a solution of intermediate strength which, in turn, was diluted 100 ml. to 1 liter to prepare a working standard solution containing 1.4893 pg, of Rr per ml. FLAVANOL SOLUTION. Eastman Kodak 3-hydroxyflavone (flavanol), lot KO. 6585, was dissolved in Eastman Kodak p-dioxane. The dioxane was purified by distillation after refluxing with sodium for 24 hours. A 0.01% solution was prepared by dissolving 0.1000 gram of flavanol in 1 liter of dioxane. The solution contains about 0.43 pmoles of flavanol per ml. STOCK BUFFERSOLUTIOS.The diluting solution contains 10.0 grams of potassium biphthalate and 8.0 grams of KaC1 per liter.
