mate a i d monochloroacetate buffers of p H 3.5 to 3.7, the current readings became constant in a fen- minutes, and increased linearly with increasing uranium(1V) concentration after one mole of uranium(1T’) had been added for every t m moles of fluoride present (Figure 6 and Table IV). For eight determinations, fluoride to uranium ratios of 1.8 to 2.1 were obtained, with an average of 1.93. Hence, the error may be as large as &lo%. I n formate buffers of pH 4.2, however, 10s- results uere obtained for the fluoride to uranium ratio, and it appears that on the addition of fluoride the uranium-formate complex changes appreciably. I n the acetate buffer, the results were qomewhat disturbing. At a pH of 4.1, fluoride to uranium ratios of 1.6 m-ere obtained. K h e n t h e pH was increased to 5.0, the ratio increased to 4 or even 5 and occasionally to 6. The current readings became constant after longer intervals and led to the rejection of the acetate buffer as a suitable supporting clectrolyte. The recommended procedure for determining fluoride is as follows.
from the solution because of the ease of uranium(1V) oxidation. Small amounts of chloride or sulfate will not interfere seriously by shifting the niercuric anodic wave to more negative potential values, but large amounts should be avoided. The main advantage of this method is that very few n-aves interfere with the uranium(1V) anodic TTave and a fluoride to uranium ratio of 2 is obtained. Otherwise. the method is not superior to existing amperometric methods for fluoride.
Twenty milliliters of formate buffer. 0.211.1 and p H 3.5 to 3.7, are pipetted
naissance de l’Uranium,” Cniversity of Paris, Imprimerie Mulhousienne, 1936. (8) Hume, D. X., Harris, IT. E., IND. ESG. CHEV., .%SAL. ED. 15,465 (1943). (9) Kern, D. 11. H., Orlemann, E. F., J . d r n Chem. SOC.71, 2102 (1949). (10) Kolthoff, I. RI., Lingane, J. J., “Polarography,” 2nd ed., pp. 462-7, Interscience, SeTv York, 1952. (11) Kraus, IC. .I.,Selson, F., J . Am. Chem. SOC.71, 2517 (1949). (12) Kritchevskr, E:. S.,Hindman, J. C., Ibid., 71, 2096 (1949). (13) McEn-en, D. J., De S-ries, Thomas, .%SAL. CHEW30, 1889 (1958). (14) Marshall. E. D., TJ.S.Atomic Energy Commission Document AECD 3289 fdeclassified Dec 21. 1951). f l 5 ) Meites, L., Meites, T.. ASAL CHEN. 20, 984 (1948). (16) Rodden, C. J., ed , “Lhalx-tical
into a polarographic cell. After deoxygenation of the solution b)- bubbling of nitrogen, the fluoride in the solution is titrated with uranium(1V) chloride or perchlorate. After each addition of reagent, the solution is stirred and :illowed to stand a few minutes until the current readings become constant. The diffusion current is measured a t about +0.10 to SO.15 volt (US. S.C.E.) and is corrected for residual current and for dilution of the polarographic solution by the titrant, Even though the oxygen wave does not interfere with the uranium(1V) anodic wave, oyygen must be removed
Table IV.
Concn. of Buffer,
Titration of Fluoride with Uranium(IV)
JI
riH
0 2
3 3 3 4 4
0 3
F--Idded, 1Ig.
Formate 5 0 6 0 7 0 2 0 2 0
46
27 46 34 51
F,V Ratio 2 1 2 1 1
0 8 1 3 4
LIonochloroacetate
LITERATURE CITED
(1) Day, R. a.,Wilhite, R . X., Hamilton, F. D., J . Am. Chem. SOC.77, 3180 (1955). (2) Flatt, R., Helu. Chim. Acta 20, 894 (1937); Angew. Chem. 50, 329 (1937). (3) Furman, N. H., ed., “Standard llethods of Chemical Analysis,” 5th ed., p. 405, Iran Sostrand, Sen- Tork, 1939. (4) Glasstone, S., “Electrochemistry of Solutions,” p. 210, hlethuen, London, 1930. (5) Harris, W.E., Kolthoff, I. 11 , J . d m . Chem. SOC.67, 1484 (1945). (6) Heal, H. G., Trans. Faradau SOC. 45, 1 (1949).(( (7) Hess, IT.> Contribution de la Con-
n 2
Ahetate 0.51 5.0 0.44 1.24 5.0 5.1 0.51
4.1 ~~
1.6
3.9 5.0 4.0
Chemistry of the Manhattan Project,” NSES, Div. VIII, p. 68, McGraw-Hill, New Tork, 1950. (17) Ibid., pp. 596-610. (18) Taylor, J. K., Smith, R . E., Cooter, I. L., J . Research A-atl. Bur. Standards 42, 387 (1949). (19) Tishkoff, G. H., “Physico-chemical Mechanisms of Uranium Transport in the Body,” Ph.D. thesis, University of Rochester, 1951. (20) Tishkoff, G. H., E.S. A4tomicEnergy Commission Document M 1719. (21) Voegtlin, C., Hodge, H. C . , eds., “Pharmacology and Toxicology of Uranium Compounds,” NSES, Div. 1-1, Vol. 1, pp. 102-46. PIIcGraw-Hill, NenYork. 1948. (22) Ibid., pp. 184-90. (23) Ibid., pp. 1124-38. (24) Vogel, K,, Silikat Tech. 4,483 (1953). RECEIVEDfor review October 27, 1958. .Iccepted April 20, 1959. Abstracted in part from the thesis submitted by D. J. McEn-en for the Ph.D. degree in chemistry, Purdue University, Lafayette, Ind.
Amperometric Titration of Barium H. E. ZITTEL, F. J. MILLER, and
P. F. THOMASON
Analytical Chemisfry Division, Oak Ridge Nafional Iaborafory, Oak Ridge, Tenn.
,An amperometric titration of barium in a medium of tetraethylammonium bromide in an ethyl alcohol-water solution is described. Lithium sulfate is the titrant and the dropping mercury electrode is the indicator electrode. The method is similar to that first described by Heyrovski and Berezicky but differs in the medium and supporting electrolyte. Because of these modifications, the sensitivity of the method is greatly increased. It was possible to titrate solutions that were 5 X 10-5M in bar-
ium with reasonable accuracy. The accuracy varies from less than 1% error in the concentrated samples-i.e., >2.5 X 10-3M-to less than 10% error in the more dilute samples-i.e.,
x
I., J . -4m. Chem. Soc. 66, 1431 (1941).
HECEII-EDfor review Decemlwr 8, 1958 AIccepted. \ p i 1 16, 1050.
Photometric Titration of Thorium and the Rare Ea rt hs with (Et hy Ie ned init riI0)tetra a cet ic Ac id KAZlMlERZ Y. BRIL, SONJA HOLZER, and BELA RETHY Research laboratory, Orquima S.A., Suo Paulo, Brazil
b Thorium and the rare earths are titrated with (ethylenedinitri1o)tetraacetic acid using Alizarin Red S as indicator. Photometric end point d e tection increases the sensitivity o f the method. Determinations can b e made a t concentrations as low as 5.1O-'jM. In the case of the cerium group rarp earths, the method allows simultaneous determination of both thorium and the r a r e earths. As little as 0.1 o f thorium in the rare earths, o r 0.2y0of the r a r e earthsin thorium,can b e evaluated. The interference of cerium i s eliminated b y the addition of hydroxylamine hydrochloride. The method is applied to
yo
naturally occurring mixtures, after some conventional separations.
(E
THYLESEDIXITRILO)TETRAACETIC
ACID, EDTA, forms stable complexcs with the ions of the rare earths (R+3) and of thorium. Several complexonietric procedures using various color indicators Tvere developed for the titration of these ions (10, 16). iilizarin Red S has been used as indicator for both the complexoiiietric and spectrophotometric determination of thoriuni (S, 7 , 9, 19) or the rare earths (3, 4,l ? ) . Difficulties were encountered in the
titration of the yttrium group rare earths ( 4 ) . The literature reports no systematic study of the simultaneous complexometric determination of both thorium and the rare earths in mixtures. Using phot'ometric determination of the elid point, thorium and the rare earths can be titrated with EDT.4 iisiny .klizarin Red S,as indicator. down to a concentration range of 5 x 10-"M. S o difficulty was encountered in the determination of yttrium and erbium. In the case of the cerium group rare earths (up to europium), simultaneous determination of thorium and the rare earths was found possible. As little 21s 0.1% VOL. 31, NO. 8, AUGUST 1959
1353
