V O L U M E 2 6 , N O . 11, N O V E M B E R 1 9 5 4
1797
ville, Calif., \vlio reviejvcd the paper. Financial support j v : ~ ~ (12) Kooijman, P. L., and Ghijsen, W.L., Rec. Iran. ciii~n..66, 205 (1947). received from the Office of S a v a l Research under Contract No. (13) MacPievin, W. M.,and Urone, P.F., AX.IL. CHEM.,25, 1760 S5ori-07819, S R 092-008. (1953). (14) Reichert, J. S.,AIcSeight, S. A, and Rudel, H. W., IND ESG LITERATURE CITED CHEM.,ANAL.ED.,11, 194 (1939). (15) Rieche, A., and Meister, I t . , Rer., 66B,718 (1933). Boyd, AI. J., and Logan, AI. A , J . Biol. Chem., 146, 279 (1942). (16) Satterfield, C. S . , and Case, L., I d Eng. Chem , 46, 998 Bricker. C. E., and Johnson, H. R., IXD.EXG.CHEK, - 4 s . 4 ~ . (1954). ED., 17, 400 (1945). (17) Satterfield. C. 5 . . Wilson, R . E., Cooper, D. O., and Stein, Brochet, 4.,and Cambier, I t . , Conzpf. rend., 120, 449 (1SD5), T. W., Ibzd., 46, 1007 (1954). Bryant, W.11. D., and Sinith, D. AI,, J . Am. Chem. Soc., 57, 57 (18) Schultes, H., Angezi,. C h o n , 47, 258 (1934). (1935). (19) Stern, V., and Polak, S.,-4cta Ph~sicoehzm. C.R.S.S., 11, i 9 i DenigBs, G., Conipt. r e ~ i . 150, , 529 (1910). 11939). Dickey, F. H., Raleg-, J. H., Rust, F. F., Treseder. R. S.,and (20) Wagner, C. D., Cleyer, H. L., and Peters, E. D., A s . 4 ~ .CHEM., Vaughn. W.E., I d . Eng. Chem., 41, 1673 (1949). 19, 980 (1947). Dunica, B. L., Perrin, D . D., and Style, D. W.G., Trans. Fara(21) Wagner, C. D., Smith, 11. IT., and Peters, E. D . , Ibid., 19, 962 d a y Soc.. 47, 1210 (1951). (1947). Eegriwe, E., 2 . anal. Chem., 110, 22 (1937). (22) Ibid., p. 976. Egerton, A. C., Smith, F. L., Ubbelohde, A. R., T r a n s . Roy. SOC. (23) Walker, J. F., "Formaldehyde," 2nd ed., -1.C.S. Monograph 120, (Londonl, A234, 433 (1935). New York, Reinhold Publihhing Corp., 1953. Kingsett, C. T.. J . Citeni. Soc., 37, 792 (1880). (24) Walsh, A. D., Trans. Faraday Soc., 42, 271 (1916). Kokatnur, V. I t , , and Jelling, AI., J . A m . Chem. Soc., 63, 1432 RECEIVED for review April '27, 1il.3. Accepted ,July 16, 1954. (1941). ~I
lithium Isotope Determination by Neutron Activation LOUIS KAPLAN and K.
E. WILZBACH 111.
Chemistry Division, Argonne N a t i o n a l Laboratory, Lemont,
The large absorption cross section of lithium-6 for thermal neutrons, with the resultant production of tritium, is utilized for the isoLopic determination of lithium. Solutions of Itnow n lithium concentration are irradiated in a nuclear reartor. The tritium produced affords a direct measure of the relatibe lithium-6 content of the solutions. The only significant interference is from lithium impurity in the quartz irradiation tube. The precision of a lithium-6 determination is within 1%.
THE
Fotopic contents of lithium samples have been detcimined i- by means of optical spectroscopy (1, 1 0 ) as well as by mass spectroscopy (for recent references see 9). The present paper presents a method for the determination of lithium-6, which makes use of the nuclear reaction Lie(nla)H3. Comparison of the amount of tritium produced in the unknown with that from a standard permits the evaluation of the lithium6 content of the unknown. The tritium production should be directly proportional to the lithium-6 content, since the only other processes known to produce tritium under pile-irradiation conditions are the ( ?,a)-reaction on lithium-i ( 8 ) , the (n,?)-reaction on deuterium (61, and the reactions of fast neutrons with boron ( 2 ) and nitrogen (2, 3). The cross section of none of these reactions is large enough to cause any difficulty under ordinary conditions. Interference by other radionuclides which might be formed during the iriadiation is likewise not apt to be seiious, as hydrogen is readily separable from all other elements. [11 method utilizing the same nuclear reaction, but measuring the darkening of a photographic plate by the reaction products has recently been described (4).]
amount of each salt was niade up to volume with distilled water, and a further t,enfold dilution of each was made volumetrically. T h e concentrations of the solutions calculated from the weight of lithium sulfate (using for the enriched lithium an atomic weight of 6.065) were checked by flame-photometric analysis. hbout 0.5-ml. aliquots of each solution were weighed into quartz ampoules of 7-mm. outside diameter, which were then cooled in liquid nitrogen, evacuated, and sealed off. Blanks of distilled water and 0.1-V sulfuric acid were prepared similarly. T h e six ampoules were placed side by side in an aluminum container which was irradiated in a pile for 2 weeks a t a flux of about IO'? neutrons per sq. cm. per second. Each ampoule was then opened on the vacuum line, and the gas which was not condensed by liquid nitrogen was transferred by means of a Toepler pump to an ion chamber for tritium analysis (12). The water was distilled and 10-mg. aliquots were analyzed (11, 12) in triplicate hy conversion to hydrogen wit'h zinc in a sealed tube. RESULTS 4 N D DISCUSSION
Thc results are summarized in Table I. For esch lithium sample, t,he net amount of t'ritium produced, the total amount minus the blank, is seen to be directly proportional to the lit,hiuin concentration; the yield per lithium atom does n o t differ by mJre t h m 0.6% for a tenfold difference in concentration. The value calculated for the natural lithium sample, using the stated value of 95.2% lithium-6 for the enriched sample, is 7.49% lithium-6. This result may be compared with natural abundance values of .30 to 7.46% from recent' mass-spectrometric studies (Q), 7.62
-.
from the chemical atomic weight, and 7.98 from x-ray and densit!. measurements on lithium fluoride ( 5 ) . The loxver limit to the amount of lithium-6 vhich can be used
PROCEDURE
T w o samples of lithium sulfate were used. One, obtained from Oak Ridge, was stated to have t,he isotopic cornpositmion95.2 i: 0.1% Li6, 4.8 =tO.l%l, Li7. The other was prepared from shelf lithium carbonate (Merck). Both samples were fumed t,o constant weight with sulfuric acid. S p e c t,r o g r a p h i c analyses showed insignificant srnounts of m e t a l l i c i m p u r i t i e s . -4weighed
Table I. Concn., Solution
,V
HzO H2804 (enriched) LitSOa(natura1)
0.1 0.00941 0.000941 0.1105 0.01105
Lithium Isotope Determination Tritium Content, pc./Ml. Soin. Gas Liquid Total Set 0.08 0 16 1 0 . 0 2 0.24 0.11 0 133 1.0.003 0.24 17.8 278 0 1.0.4 295.8 295.6 1.21 28.73 1.0.06 29.94 29.70 16.2 258 6 i o4 274 8 274.6 1.30 26.22 5 0 05 27.52 27.28
T/Li, C . / G . Atom 31.41 31.56 2.485 2.469
1798
ANALYTICAL CHEMISTRY
for a detormination is set by the magnitude of the blank. The unexpectedly large value of this blank has heen shown t,o result from lithium impurity in the quartz tubing used in this investigation. The concentration of lithium found in the quartz by flame photometric analysis of the residue from hydrofluoric acid treatment was 5.9 p.p.m.; t h a t calculated from the tritium recovered by heating a n irradiated tube at 600" C. was 5.5 13.p.m. Fortunately, only a very small fraction of this tritium passes into the sample a t room temperature; the measured blank is equivalent to ahout 0.02 y of lithium-6. The large absorption ( T O S S section (about sq. cm.) of l i t h i u m 4 sets an upper limit. to the amount of sample that can he tolrratcd without the introduction of significant error h y "selfs1i:tdowing." For a mean path length of 0.5 cm., a solution 0.03.1.' in lithium-6 would cause a 1% attenuation in the neutron flus. T h a t this effect is not serious under the conditions of the esperiment for solutions less than 0.01S in lithium4 is demonstrittrd by the propxtionality between tritium production and lithium concentratbn. The irradiation exposure could be considerably lcss th:tn that used in these experiments. The more dilute solut,ioris listed in Table I yielded about 0.3 microcurie of tritium from :L IO-mg. aliquot; a hundredth of this quantity can be measured with :L precision within 1% ( 1 2 ) . Any method of determination of total lithium may I)c used i n conjunction with the tritium measurement in order to compare the isotopic content of lithium samples. The data in Table I are based on v-eighing ?he sulfate; satisfactory results have it130 I)ren obtained by flame photometry. For absolute determinations, separated lithium-6 of high isotopic purity, available from Oak Ridge, may be used as a standard.
In principle, the lit,hium-6 content of a saniplc can I)e culculated from the tritium production and the neutron exposure. T h e neutron flux is, however, seldom known with sufficient accuracy for this purpose. In fact, the production of tritium from lithium has been used to measure the neut,ron flus in determining the iieutro~i:tl~sorptioncross section of deuterium ( 6 , 7 ) . ACKNOWLEDGMENT
T h e authors are indebted to J. K. Rrodj. for the lithium sulfate standards, and to R. W, Bane, J . P. Fnria, and J. A. Goleb for lithium determinations. LITERATURE CITED
Hrody, J. K., Fred. >I.. and Tompkins, F. S., J . O p / . SOC.A m e r . , 42, 870(A) (1952) : paper presented at Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. >larch 1 to 5 , 1954. Cornog, R., and Libby, W. F..Piiys. Rei'., 59, 1046 (19411. Fireman, E. L., Ibid., 91, 922 (1933). Herr. W.,2. .Yaticrforsciz.. a8, 305 ( I 9 3 ) . Hutchiaon, D. A , . Phgs. Ret.. in press. Kaplaii. L., Ringo, G . R..and Wilzbnch. IICSally, J. It., Jr., J . O p t . SOC.Au7er., 42, 883 (1952). Wilzbach, K. E., Kaplan, L., and Brown. If'. G., Science. 118, 522 (1953). Wilabach, K. E., Van Dyken, -1.R., and Kaplan, I. .. AX.AL. CHEM., 26, 880 (1954). RECEIVED for rei l e x May 27, 19.54, .iccepted:.iugrist
20, 19d4.
Determination of Hypophosphite in the Presence of Phosphite D. N. BERNHART Research Laboratory, Victor Chemical
Works, Chicago Heights, 111.
Hypophosphite can be oxidized quantitatively to phosphite by cerium(1V) in sulfuric acid solution. The excess cerium(1V) is determined by titration with iron(I1) solution using ferroin as an indicator. The reaction is complete in 1.5 hours at room temperature or in 30 minutes at 60" C. Although the reaction as prescribed stops at the phosphite stage, further oxidation to phosphate is achieved by raising the temperature to 80" or 100" C. Either phosphite or hipophosphite is oxidized quantitatively to phosphate when boiled for 15 minutes in an excess of reagent. This new ceriometric method may therefore be used for the determination of hypophosphite ion in the presence of phosphite and phosphate, of phosphite ion in the presence of phosphate, or of both hypophosphite and phosphite if total lower valent phosphorus must be determined.
B
ECAUSE hypophosphites and hypophosphorus acid have become more and more useful for a number of commercial
applications and most commercial grades contain small amounts of phosphite, an analytical procedure is needed for ?he quantitative determination of hypophosphite in the presence of phosphite. Jones and Swift ( I ) have shown t h a t hypophosphite does not interfere in t h e quantitative determination of phosphite, which can be oxidized quantitatively with iodine under proper conditions. Such a titration must be carried out in neutral solution;
this requirement represents a disadvantage, as the calcium and barium phosphites, both commercially available at the present time, are insoluble. The iodometric procedure is rather specific for phosphite and is satisfactory if only small quantities of hypophosphite are present. The accuracy of the method falls off, however, when small amounts of phosphite are present, especially in compositions a h i c h consist essentially of hjpophosphite. Considering that the iodometric procedure, even under the best conditions, is more or less specific for phosphite, the purity of a sample of hypophosphite can then be determined only by difference Other osidizing agent leagents such as hot permanganate, mercuric chloride, and potassium bromate oxidize both phosphite and hypophosphite t o phosphate. Although these reagents can be used t o determine either or both constituents, indirect methods
Table I.
Determination of Hypophosphite by Procedure A RaPOz
HIPO1
Taken,
Mg
Taken, hlg.
61.10
1 .oo
81.10
3.00
HaPOz F o u n d , AIg 61 06 61.04 61,lO 61.03 61.08 61.05
61.10
5.00
61.06 61.09 61.09
