thereby making the method easily learned by a technician. One of the chief advantages of the method is the extreme versatility in handling samples of different sizes and yttrium concentration. Although the ion exchange procedure could be adapted to handle samples much larger than 1 gram, solvent extraction with thenoyltrifluoroacetone might be better for this purpose. It should also be possible to determine elements of the rare earth group by this method, but the author has done no work along these lines. ACKNOWLEDGMENT
The author is indebted to Hilbert
R. Siegler, Helenette Silver, and Laurance E. Webber for their cooperation in carrying out this study after the author had left the University of New Hampshire.
LITERATURE CITED
(1) Am. SOC. Testing Materials, Philadelphia, Pa., Photographic Photometry (E116-56T, 1956)in “Methods for Emission Suectrochemical Analysis.” Section 9, 1957. (2) Butler, J. R., Spectrochim. Acta 9, 332 (1957). (3)Edge, R. A., Brooks, R. R., Ahrens, L. H., Amdurer, S., Geochim. et Cosmochim. Acta 15, 337 (1959). (4) Fassel, V. A,, J . Opt. SOC.Am. 39, 187 (1949). (5) Fassel, V. A., Cook, H. D., Krotz, L. C., Kehres, P. W., Spectrochim. Acta 5,201 (1952). ( 6 ) Fassel, V. -4., Quinney, B. B., Krota, L., Lenta, C., ANAL. CHEM.27, 1010 (1955). ( 7 ) Fassel, V. A., Wilhelm, H. A., J . Opt. SOC.Am. 38.518 (1948). (8) Feldman, ‘C., Ellenburg, J. Y., ANAL. CHEM.30,418 (1958). (9) Hettel, H. J., Fassel, V. A., Ibid., 27, 1311 (1955). (10) Kinseley, R. N., Fassel, V. A., Tabeling, R. W., Hurd, B. G., Quinney, B. B., Spectrochim. Acta 13, 300 (1959). (11) MacDonald, N. S., Nusbaum, R. E., “
I
Alexander, G. V., Ezmirlian, F., Spain, P., Rounds, D. E., J . Biol. Chem. 195, 837 (1952). (12) Morris, J. M., Pink, F. X., “Symposium on Spectrochemical Analysis of Trace Elementa,” p. 39, Am. SOC. Testing Materials, Philadelphia, Pa., 1957. (13) Owens, E. B., Appl. Spectroscopy 13, 105 (1959). (14) Schubert, J., Russell, E. R., Farabee, L. B., Science 109,316 (1949). (15) Waring, C. L., Mela, H., ANAL. CHEY.25,432 (1953). RECEIVED for review February 15, 1960. Accepted December 2, 1960. Final report on one phase of Federal Aid to Wildlife Project FW-2-R, conducted cooperatively by the Research and Management Division of the New Hampshire Fish and Game Department, and the Engineering Experiment Station, University of Yew Hampshire. Twelfth annual Meeting-in-Miniature, Iiorth Jersey Section, ACS, February 1, 1960. Paper of the Journal Series, New Jersey Agricultural Experiment Station, Rutgers, the State University, Department of Soils, New Brunswick.
Spectrophotometric Determination of Technetium with Toluene-3,4-dithiol FRANCIS J. MILLER and PAUL F. THOMASON Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tenn.
b A method has been developed for the spectrophotometric determination of technetium in the microgram range by reaction with toluene-3,4-dithiol in an aqueous medium that is 2.5N in acid. The colored complex that is formed is extracted into carbon tetrachloride. The intensity of the color of the carbon tetrachloride solution is measured at 4 5 0 mp. The molar absorptivity is of the order of 15,000. The interference of many metallic cations necessitates the preliminary separation of the technetium. The results of a study of the various factors that influence the formation and extraction of the complex are presented.
T
presented herein is the outgrowth of work done previously on the colorimetric determination of technetium with thioglycolic acid (4). Although the thioglycolic acid method suffices for the rapid determination of technetium and is especially suitable for a ranging procedure, it lacks sensitivity. Also, a colorimetric reagent for use in a solution of low pH R-ould be advantageous. d short search of the literature disclosed the long-known colorimetric reagent, toluene-3,4-dithiol, or simply dithiol. Sandell (6) lists this reagent HE STCDY
404
ANALYTICAL CHEMISTRY
and discusses its use as a colorimetric reagent for the determination of tin, tungsten, and molybdenum. Clark (6) has demonstrated the applicability of toluene-3,4-dithiol to the determination of many other metals. Morrison and Freiser (5) discuss the extraction of the bidentate complex of molybdenum with toluene-3,4-dithiol into an organic solvent. Gilbert and Sandell have characterized the Mo-dithiol complex as a tridentate complex in a thorough investigation (3). The investigation described herein has shown that toluene-3,4dithiol is also suitable as a colorimetric reagent for the determination of technetium when it is present as pertechnetate ion. Many elements interfere. Adequate means of separating and isolating technetium from other elements are known and have been discussed by Boyd ( 1 ) . A review article by Clark and Neville (6)list the conditions under which toluene-3,4-dithiol reacts with various ions to produce colored species. EXPERIMENTAL
Standard Solution of Potassium Pertechnetate. This solution contained 0.423 mg. of potassium pertechnetate, KTcO.,, per ml. Spectrographic analysis showed no impurities present.
Toluene-3,4-dithiol Solution. This solution was prepared by dissolving 5 grams of toluene-3,4-dithiol, CH8C6H3(SH)2,and 12.5 grams of thioglycolic acid, HSCH2COOH, in l liter of a 2.5 w./v. ?& , ,- solution of sodium hydroxide. This method of preparation is taken from a previous report (7‘). If prepared in this manner and stored in a polyethylene bottle, the reagent should be stable for a Deriod of at least 2 weeks. The dithiol solution does oxidize slowly on standing and should be checked against a standard calibration curve before use. Purified Carbon Tetrachloride. The analytical reagent grade carbon tetrachloride was further purified by shaking it first with a solution of ceric sulfate, then with a solution of sodium carbonate, and finally with distilled water. Apparatus. A Cary Model 14PJI recording spectrophotometer, with cells of 1-cm. light path, was used t o obtain and to record all spectral data. Procedure. Ten milliliters of purified carbon tetrachloride was placed in a 30-ml. separatory funnel; the funnel was equipped with a Teflon stopcock to avoid the presence of stopcock grease in the carbon tetrachloride. Two milliliters of water was added. Two milliliters of the toluene-3,4-dithiol reagent solution was placed in the funnel, and a suitable aliquot of the standard solution of
‘3
Instrument, Cory model I4 PM C e l l , t Crr. Reference. corbon letrac?loride extract of blank Composition of solifions,
c
Table I.
Effect of Acids
(Vol. of aqueous phase 5 ml.; Tc present, 41.40 pg.; vol. of CCll phase, 10.0 ml.) Absorbance of CCl4 P h a s e Acid 450mfi 530mp HCl 0.665 0.365 HClOa 0.710 0.400 0.730 0.320 ”01 0.260 0.000 CH3COOH 0.245 0.105
-, -.
..rx
,
~
4-30
5000
-
LE\GT-I
55COA.
6322
I=”L
Figure 1. Effect of dithiol concentration on the absorption spectrum of the pertechnetate-dithiol complex
potassium pertechnetate added. One milliliter of concentrated hydrochloric acid was then added. The funnel was stoppered and JTas shaken a t intervals of 15 minutes for a period of 1 hour. The carbon tetrachloride layer was then drained off through a filter paper into a IO-ml. flask. The absorption spectrum of the carbon tetrachloride solution was recorded with a Gary Model 14PhI spectrophotometer; the reference solution mas the carbon tetrachloride extract of a reagent blank. A plot was made of the weight of technetium in the test aliquot of the standard solution of pertechnetate against the absorbance a t 450 mp. Test solutions of samples were treated in a similar manner. DISCUSSION
One of the first factors relative to the pertechnetate-dithiol reaction was the effect of the organic solvent in the extraction of the chelate from the aqueous phase. When the chelate was extracted with amyl acetate (City Chemical Co.), a single rather sharp absorption band of maximum a t 540 m p was observed in the spectrum. With Fisher Chemical Co.’s purified amyl acetate, the maximum was a t 530 mp, and the band had a very broad, trailing edge. If cyclohexane was used as the extractant, two absorption bands appeared, one of maximum a t 530 mp, and the other a t 450 mp. When the solvent was carbon tetrachloride, the 530-mp band almost disappeared, and the intensity of the 450-mp band was greatly increnced. The choice of the solvent is of considerable import in the formation of the chelate. Carbon tetrachloride n-as selected as the solvent because it suppresses the one band and intensifies the other band. Other solvents were studied, but they rhomed no advantage over carbon tetrachloride. A study of the effect of hydrochloric, perchloric, sulfuric, nitric, and acetic acids, each in a 2.5N concentration in the aqueous phase, was made. The results are given in Table I. The order of addition of the reagents was studied. If the aqueous sample and
the reagents n ere mixed and allon ed to stand, that species which shows maximum absorbance a t 530 mp tends to predominate. If the carbon tetrachloride is added first to the separatory funnel and then the aqueous reagents and test aliquot are added, that species which shows maximum absorbance a t 450 mp predominates. In either case, the color of the organic phase that contains the extracted chelate is stable; no change in the color occurs over a period of 12 hours. The effect of the acid concentration of the aqueous phase on the formation of the chelate species mas also studied. If the aqueous phase was less than 0.2N in acid, no color developed. At 0.2W acid concentration the golden color (450 mp) appears but is not intense. At 0.4.N acid the rose-colored species (530 mp) is favored. An increase in the acidity t o 0.6N produces conditions that again yield the golden-colored species. There are evidently ranges in acid concentration that favor one species over the other. Because the intensity of the color continues to increase until an acid concentration of 2.ON is reached, it is recommended that the acid concentration of the aqueous phase be kept above 2.0-1.
A crossover point in reagent concentration also exists where one species is favored over the other. The formation of the rose-colored species is favored a t the smaller concentrations of dithiol; the larger concentrations definitely favor the gold-colored species. A large excess of reagent is not detrimental. Although the reagent is precipitated in the aqueous phase, only the colored complex is extracted into carbon tetrachloride. No extraction of the dithiol reagent itself was observed under the stated conditions. The spectrum of the solvent showed no change when tested for the extraction of dithiol. The effect of reagent concentration on the absorption spectrum is shown in Figure 1. It became increasingly evident as the study of the pertechnetate-dithiol reaction progressed that a t least two
Table II. Beer‘s Law Data (Vol. of aqueous phase, 5 ml.; vol. of CCla. 10.0 ml.; acid concn., 2.5N HCl; cell length, 1 cm.j Tc in Aqueous Absorbance of Phase, pg. CCh Phase 6.21 0,092 12.42 0.180 16.56 0,245 20.70 0.332 41.40 0.670 82.80 1.310
species of the chelate complex can exist in solution. Efforts made to characterize the species present have been unsuccessful. In one study, the concentration of the pertechnetate ion was held constant, and the concentration of the reagent was varied over a wide range. Spectra were taken and were then analyzed mathematically to calculate the absorbance resulting from each species. It was not found possible, even by use of these data, to calculate equilibrium constants for the chelate species. I t is possible to maintain conditions that definitely favor the formation of one species and largely suppress the formation of the other. The conditions that favor the formation of the species that absorbs a t 450 rnp are: the choice of the proper organic solvent for extraction, saturation of the aqueous phase with carbon tetrachloride prior to the formation of the chelate, adjustment of the acid concentration of the aqueous phase to a minimum of 2.ON, and the use of a large excess of reagent. A plot of the data of Table I1 shows that a linear relationship exists between the concentration of technetium in the aqueous phase and the absorbance of the carbon tetrachloride extract over the concentration range from 1.5 to 16.5 pg. per ml. An average molar absorptivity of 15,000has been calculated. The over-all error does not exceed a relative standard deviation of +5y0. If the extraction is made by shaking the two phases together by means of a mechanical shaking apparatus, 15minutes shaking time a t room temperature is sufficient to attain equilibrium. There is no advantage to be gained by shaking the phases for a longer period. If the separatory funnels must be VOL. 33,
NO. 3, MARCH 1961
405
shaken by hand, it is better to shake them at intervals of 15 minutes for a period of 1 hour.
the ORNL Chemistry Division who kindly supplied the standard solution of potassium pertechnetate.
ACKNOWLEDGMENT
LITERATURE CITED
The authors are indebted to R. E. Biggers for the many machine calculations made in determining the aborbances of the various species and to J. M. Chilton for his help in attempting to estimate the equilibrium constants. The authors also thank Q. V. Larson of
Extraction in Analytical Chemistry,” pp. 22, 180, 219, 240, Wiley, h e w York, 1957. (6) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 2nd ed., pp. 130, 565, Interscience, New York, 1m.
(1) Boyd, G. E., J . Chem. Ed. 36, 39 ( 1959). (2) Clark, R. E. D., Keville, R. G., Zbid., 36, 390 (1959).
(3) Gilbert, T. W., Sandell, E. B., J . Am. Chem. SOC.82, 1087 (1960). (4) Miller, F. J., Thomason, P. F., ANAL.CHEM.32, 1429 (1960). (5) Morrison, G. H., Freiser, H., “Solvent
( 7 ) United
Kingdom Atomic Energy Authority, PG Rept. : 2 5 ( s ) , September 4, 1959.
RECEIVED for review July 27, 1960.
Accepted November 14, 19G0. Oak Ridge National Laboratory is operated b.y Union Carbide Gorp. for the C. S. Atomic Energy Commission.
Determination of Dissolved Radium A. S. GOLDIN’ Radiological Health Research Activities, Division of Radiological Health, Robert Cincinnafi, Ohio
b Radium carried on barium sulfate is determined by alpha counting. The radium is concentrated from solution by coprecipitation with mixed barium and lead sulfates. The lead and barium carriers are added to a solution containing alkaline citrate, which prevents precipitation until complete interchange has been accomplished. Sulfuric acid is then used to precipitate the carriers and the radium. The barium sulfate is purified by nitric acid washes and is reprecipitated from EDTA solution by treatment with acetic acid. The EDTA masking serves to purify from other naturally occurring alpha emitters and from the lead carrier. Decontamination from other alpha emitters is shown and the problems involved in specific determination of any of the radium isotopes are discussed. Isotopic nature of the radium is determined by measurement of ingrowth or decay. Growth and decay curves for radium-226, radium224, and radium-223 are presented.
T
HE DETERYIN.4TION
Of
radium-226
at levels of a few micromicrocuries (or picocuries) which is a unit of curie has become a matter of considerable public health interest. The occupational maximum permissible concentration (MPC) of this nuclide in drinking water is lo-’ pc. per ml. (6), or 100 picocuries (pc.) per liter, which is lower than that of any other radioisotope. For application to the general public, levels as low as 1 to 10% of this are of interest (7). Radium is present in uranium ores to an extent which varies somewhat, but is roughly comPresent address, New York University Medical Center, New York 16, N. Y .
406
ANALYTICAL CHEMISTRY
A. Tuff Sanitary Engineering Center,
parable to the equilibrium amount of 300 mc. per ton of uranium. Considering the extent of our uranium industry, the introduction of any appreciable fraction of this radium into public water supplies could be of great importance. For this reason, methods for the determination of radium which would be suitable for use by state and other public health agencies have been investigated. The method would have to be sufficiently sensitive to permit determination of radium at a level of 5% of the M P C or less-i.e., 5 X pc. per ml. ( 5 pc. per liter)-without interference from larger quantities of other natural alpha emitters. It should be applicable to radium in waters of a wide variety of mineral content, particularly those with a high sulfate content, and should be simple to permit analysis by technicians familiar with equipment commonly found in chemical laboratories and measurement by routine counting equipment. A method which did not require long periods for ingrowth or decay of radioactive materials would be preferable. Two methods are commonly used for radium determination-measurement of the gaseous radon daughter or coprecipitation with barium salts, especially sulfate. Determination through the radon daughter, although a method of choice under suitable conditions, was ruled out because a rather long waiting period is required unless it is known that radioactive equilibrium has been attained. I n addition, specialized equipment is required for handling the counting radon gas. Several problems must be considered in the determination of radium on barium sulfate. Naturally occurring sulfate ion may cause premature pre-
cipitation and thus prevent interchange of the radium and barium. Although radium can be adsorbed on barium sulfate, this adsorption is hindered by substances which might be present in many waters (6). Unless the barium carrier is restricted to a very small quantity, excessive self-absorption losses in alpha counting will occur. Finally, since very small quantities of radium may have to be determined in the presence of much larger quantities of other alflha emitters, very good decontamination is required. REAGENTS
Ba(NOq).. 0.10N Pb(N0jj;j 1N Citric Acid, H3C~H607,1J1 (should contain 0.1% phenol to prevent biological growth). PROCEDURE
Add about 5 ml. of citric acid to the sample and make it alkaline with ammonium hydroxide. Add 2 ml. of lead carrier and 1 ml. of barium carrier. Heat t o boiling and add sufficient sulfuric acid (1 to 1 by volume) to precipitate substantially all the lead (This may be done by adjusting to pH 1 with a meter, by adding about 0.25 ml. in excess after neutralizing to methyl orange or methyl red, or simply visually by the amount of precipitate.) Collect the precipitate; wash it twice with concentrated nitric acid. Dissolve the precipitate in alkaline EDTA (disodium salt, 0.25111) and reprecipitate the barium sulfate by dropwise addition of glacial acetic acid in excess. When necessary, repurify the barium sulfate by a second solution in alkaline EDTA and reprecipitation with acetic acid. In this case, add a little ammonium sulfate to the EDTA solution to ensure complete precipitation. Wash the barium sulfate precipitate and transfer to a planchet for counting.
