Determination of Dissolved Polonium-210 in Water by Coprecipitation with Tellurium by Stannous Chloride D. E. RUSHING Colorado River Basin Water Quality Control Project, U. S. Department of Health, Education, and Welfare, 7 750 South Redwood Road, Salt lake City, Utah 8 4 704 The efficient coprecipitation of polonium-2 10 with tellurium by stannous chloride as precipitant is applied to the determination of polonium-2 10 in water. The doubly precipitated tellurium-polonium-2 l 0 precipitates are alpha counted on 0.22-micron membrane filters. A short-cut single-precipitation method is also given. Methods were tested a t six levels of polonium-2 10 activity (0.06 to 1636 pc. per liter); in this range, the weighted average recovery was 98.8% for both methods. Radiochemical specificity is very good; there are no interferences from stable substances in samples whose compositions approach drinking water standards. The methods have sufficient sensitivity to permit their use in the determination of lead-2 10 in water by polonium-2 10 ingrowth.
I
K STUDIES of
the radioactive pollution of the Colorado River Basin, it became necessary to determine 210Pb and ZlOPo concentrations in natural and polluted waters and in uranium mill efluents. The permissible concentrations for 2lOPo for such media are high as compared to those of zlOPb(4, 9 ) , but the accurate determination of low concentrations of 210Po is important since 2loPb can be determined by the ingrowth of Z1OPo. The 30-day ingrowth of 210Po from 210Pb is 10.9% if zlOBi is absent and 13.9% if the *lOPb to 210Biratio is 1: 1; therefore, sensitive 210Pomethods are needed for this approach to 210Pb determinations. From acid solutions, 210Podeposits to some extent by displacement on many metals-e.g., Ag, Xi, Fe, Au, P t , and Cu-and methods based on this principle are quite popular (1, 2 , 5-8, 12, I S ) . Although excellent results usually can be obtained by the methods on chemically simple samples, the methods require the control of a large number of variables and may require preliminary separation of the z10Po from a chemically complicated mixture. Broadly speaking, organic matter, oxidants, and elements which also deposit on the metal tend to interfere. Some of these interferences can be masked or eliminated by valance 900
0
ANALYTICAL CHEMISTRY
changes; other interferences require preliminary separations or treatments. I n the writer’s experience, recoveries of 210Poon silver foil have varied from 85 to 100% without obvious reason for the lower recoveries. “This ease of deposition. . . .has probably hindered the development of procedures based on newer methods. . . .” (6). The writer agrees. Frisch and Feldman inferred from limited data that the deposition on silver is highly dependent upon temperature and that the bath temperature must be 97” C. or higher ( 8 ) . This temperature is not reached by boiling water in many mountainous locations. Bismuth-210 and 21nPbare deposited on some of the baser metals used in some methods ( 3 ) . While these radionuclides are beta-emitters, they decay to alpha-emitting products. For this reason, the deposited 210Po must be alpha-counted immediately after its isolation if 210Pb and *IoBiare present in significant amounts. The writer has observed unidentified alpha growth on silver foil used to deposit 210Po. Both T e and Se, when precipitated with SnC12, can carry 210Poquantitatively. Under some conditions, the writer has observed that Se does not carry 210Po; this behavior seems to be associated with the prevailing digestion conditions. Such failures have not been observed with Te. Both elements seem to carry some Sn with them physically or in chemical combination. Rundo coprecipitated 210Powith T e using NaH2P02as the precipitant, but completed the analysis by plating the 2lOPo. Recoveries of 210Pofrom biological samples averaged about 85% (10). I n 1954, the writer observed that 21OPo was coprecipitated essentially quantitatively with Te if SnC12was the precipitant. A limited study on urine samples showed promise, but was given up for the lack of a suitable mounting technique. Further limited work has been reported (11). Lindner recovered about 98.8% of the 206Pocoprecipitated with several mg. of T e from 0.3AVto 3.05 HC1, using SnClz as the precipitant (6). Since he centrifuged, i t is likely that some of the loss was mechanical. The aims of this investigation nere to develop a method for zloPoin water
which would be applicable to other more complex media and to check the sensitivity, accuracy, and precision of the method with the idea of using it for *l0Pbdeterminations also. EXPERIMENTAL
The experimental work consisted principally of the following: (a) tests of various mounting techniques; (b) analyses of water samples containing added 210Po by the recommended procedure and of doubly precipitated standards: (c) analyses of 1-liter water samples containing added zlOPousing a single cold precipitation of the Te-Po; (d) tests to determine 210Polosses into filtrates and on glassware; (e) tests to determine the effects of various substances on the solubility of 210Po; and (f) .periodic recounting of Te-Po precipitates to establish the specificity of the method. Apparatus. Nuclear Neasurements Corp. Model PC-3B internal proportional counters were used for CYcounting. The counters were new, had a hemispherical detector, and would accommodate a 21/4-inch planchet. Their efficiencies were checked with a National Bureau of Standards 210Po source; all counters agreed to within *O.3yGof the average of the four. Their geometries averaged 1.984 T . The counting gas was 90% argon107, methane. NRIC No. Sp-4 2-inch stainless steel planchets were used. Reagents. Particulate matter in distilled mater and reagents may find its \vay into the final precipitate. Care should be taken to see t h a t a significant amount of foreign material is not introduced in this way. DISTILLEDWATER. Distilled water must be free of zlOPo and 222Rn. If purification is necessary, redistill; discard the distillate collected during the first ten minutes. ACID ~ I I X T C R E Pour . 800 ml. of 1 : l H2S04into 400 ml. of HzO, cool, transfer to plastic bottle, and add 400 ml. of HF (48%) and 400 nil. of HN03. Store in polyethylene or Teflon bottle. LE.4D-BISnruTH-TELLvRICN CARRIER SOLUTION.Prepare a solution containing 1.00 mg. each of Pb, Bi, and Te(1V) in 3.00 ml. of 1:3 HC1 and no nitrate. LE&D-BISMUTHCARRIER. Prepare a solution containing 0.5 mg. each of P b and Bi per ml. in 1 : 3 HBr and no nitrate. STANNOUS CHLORIDE SOLUTION.Dissolve 10 grams of SnC12.2Hz0 in 1N
in steam bath. While solution is still HCl and dilute to 100 ml. with 1 N HC1. warm, pour it into a 400-ml. glass beaker Filter through a 0.22-micron membrane containing approximately 1 gram solid filter. Prepare every few days. Filter H3B03. Transfer to a hot plate and daily. fume gently (200' C.) to remove WASH SOLUTION. d d d 0.1 ml. of fluorides. While solution is fuming, 10% SnC12.2H20to 100 ml. of 1 N HC1. oxidize organic matter by adding small Prepare daily. HYDROCHLORIC ACID-BROMINE SOLU- amounts of Kh'Oa. Cool. Rinse Teflon beaker twice with HzO from a fineTION. Dissolve 5 ml. of bromine in a tipped wash bottle and add washings liter of 111'HC1. to the glass beaker. Mix and evapURE - S E N ~ I T I V EADHESIVE. orate to remove H20. Transfer to hot Icrylon pressure-sensitive adhesive S o . plate (200" C.) and fume gently to 1080. Spray into a 400-ml. beaker; cool. Dilute with about remove "03: add ethyl acetate to dissolve. The 5 ml. H20. While the evaporation in solution should contain about 10 mg. the glass beaker is proceeding, add 10 dry adhesive per ml. Place about ml. of 1 : 3 HBr to the Teflon beaker, 0.75 ml. on a 2-inch planchet with a cover, and warm in steam bath. When dropper, rotate planrhet to spread the HK03 has been evaporated, transsolution uniformly, air-dry, and dry fer the contents of the Teflon beaker to under lamp for 5 minutes to remove the glass beaker, mix, and evaporate on solvent. HYDROXYLAMINE HYDROCHLORIDEsteam bath to remove HBr. (This treatment reduces T e and removes SOLUTION. Dissolve 20 grams of traces of "Os.) Transfer to hot N H 2 0 H . H C 1 in 1 N HC1 and dilute to plate (200' C.) and fume gently. Cool. 100 ml. with same solution. (Used T o the beaker, add 67 ml. of 1: 3 HC1 in short-cut method only.) and warm to dissolve soluble salts. BORICACID SOLUTION. Dissolve 50 Dilute with 133 ml. of H 2 0 ; heat until gram. H3U03in a liter of distilled water. solution is complete. I n some samples (Used in short-cut method only.) CaS04 may remain undissolved. If POLONIUM-210SoLumoNs. If a reCaS04 persists, heat nearly to boiling, liable standard solution is not available, stir, and continue heating for about an prepare an active solution from aged hour. Once the &SO4 goes into solu21Tb solution using recommended protion, it does not precipitate on cooling. cedure and standardize. Prepare suitIf i t persists after the hour of heating, Nitric able dilutions in 6 S "03. add additional 1 N HCl and repeat heatacid must be removed before precipitaing process until solution is effected. tion step. While solution is very hot (incipient Procedures. STANDARDIZATION OF boiling) and while stirring, add 5 ml. of I ~ o ~ o r ; 1 ~ ~ - 2SOLUTIONS. 10 Transfer SnClz solution in excess of that rea t least four small aliquots (about 50 pl.) quired to reduce any Fe present as of the strong 210Po solution to the centers of 2-inch stainless steel planchets judged by the color change. Cover beaker, digest on steam bath for one and evaporate to dryness at approxihour, and cool in water. Record date mately 100" C. Alpha-count long and time of this precipitation. enough to give the appropriate staFilter through a 25-mm. membrane tistical precision. Compare with a filter (0.22-micron). Rinse beaker and standard solution of zlOPo,if one is available. funnel once with 1N HC1-SnC12. D o not let filter run dry during filtration. Alternatively, the count rates of the No oxidizing fumes should be in room planchets are compared with a Naair. Remove funnel and filter to origtional Bureau of Standards 210Posource mounted on a 1-inch Monel disk. The inal precipitation beaker, cover, and set aside until all samples are filtered. author assumed a 27, correction for Discard filtrate unless 2loPb is to be backscattering. The results were 2.6% determined. Dissolve the Te-Po pretoo high as compared to an Intercipitate in 50 ml. of I N HC1-Br2 by national Atomic Energy Agency standard solution, which had a n estimated pouring the latter over the funnel. uncertainty of =t2%. Add 1 ml. of Pb-Bi carrier. Cover PRETREATMENT O F WATER SAMPLE. beaker, let stand a few minutes, swirl, heat nearly to boiling, and let stand Filter water sample through a 0.45for 15 minutes. Rinse and remove micron membrane filter as soon as cover, funnel, and membrane filter. possible after it is received. Add 2y0 by volume of concentrated HC1. Store Place beaker on steam bath and evapin a polyethylene container. Analyses orate contents until dry spot just apshould be started as soon after receipt pears in center of beaker. of sample as is practicable, because of Add 33 ml. of 1: 3 HCl, cover beaker, heat contents just to boiling, cool, add slow ingrowth of ZlOPo from zloPb and 210Bi. 67 ml. of HzO, while stirring add 5 ml. RECOMMENDED METHOD. Add, in of SnC12 solution, let stand one hour, increments if necessary, 1020 ml. of filter on a 47-mm. membrane filter (0.22the acidified water sample to a Teflon micron), and wash well as previously beaker (400 to 1000 ml.) and evaporate described. Do not scrub beaker. in a boiling steam bath. When all Using tweezers, transfer membrane the sample has been added and space filter to a 2-inch planchet which has is available in the beaker, add 50 ml. been coated previously with pressiireof the acid mixture and 3.0 ml. of sensitive adhesive. The filter will lie Pb-Bi-Te carrier solution and continue flat while moist. Use a blunt glass evaporation until essentially only the rod to press down the border of the filter H2S04 remains. Cool. Add 100 ml. at BO'-, go'-, and 45O-points. Finally, press down the entire periphery by of 1:9 "03 and evaporate overnight
running the glass rod around the edge of the filter. l l l o w to air-dry for about 2 minutes. Expose the planchet to gaseous K H 3 for 5 minutes in a desiccator containing 1 : 1 KH40H. Dry gently under a lamp for 5 minutes. A thermometer, in sample position, read 100' C. -1lpha-count in a low-background proportional counter on the following day or later. Correct count rate for background. Record date and time of counting. Calculate the 210Po concentration in the water sample. Decay correction beyond the first precipitation is complicated by possible presence of other radionuclides which produce 21OPo. Decay tables are given in the literature (11).
SHORT-CUTMETHOD. I d d 1000 ml. of water sample (or 1020 nil. of water acidified with 2% by volume of 12AV HC1) to a 1500-ml. beaker. Add sufficient HC1 to make the solution lAr. Add 3.0 ml. of Pb-Bi-Te carrier. Add 5 ml. of 20y0 N H 2 0 H . H C 1solution and let sample stand 10 minutes. Add 20 ml. of 5y0 H3B03 solution, add 1 ml. (20 drops) of 48y0 H F , and mix. d d d 25 ml. of 10% SnC12 solution and let stand for 1 hour. Filter on a 47-min. membrane filter (0.22-micron) and wash with I S HC1-SnC12 as described previously. Mount and count the filter as directed in the recommended procedure. If the activity is high enough to warrant positive identification, treat the filter as directed in the following paragraph. WET-A\SHIKG O F J I E h I B R A N E FILTERS. Noisten the filter on the planchet with CHCla and transfer it to a 250-ml. beaker; add 10 ml. of 1 : l HCl plus Br and 1.0 ml. of Pb-Ui carrier; evaporate to dryness on a steam bath; add 10 ml. of 1 : l "03; evaporate to dryness on a steam bath; add 10 ml. of 607, HC104, cover and heat on hot plate (200' C.) until acid just darkens; add "03 drop by drop (or K S 0 3 ) until the acid clears and the dark color disappears; digest on the hot plate for 1 hour; cool, remove cover, and rinse it and sides of beaker with a little H20; add 5 ml. of 1 : 3 HBr and evaporate on steam bath until the HC104 becomes decolorized and golden crystals appear. Add a few mls. of HzO and evaporate to HC1O4 on steam bath. Add 67 ml. 1 : 3 HC1, heat nearly to boiling, cool, add 133 ml. of H20,and reprecipitate the T e with 5 ml. of 10% SnC12 solution. Continue as in the previous paragraph. Polonium-210 will not volatilize under the conditions of the wet-ashing, but the result will be low by an average of 1.47, because the second loss on glassware is not compensated for by the standards. CONCENTRATIOK
OF
FILTRATES.
Sometimes it is desirable to reduce the volume of the filtrates b y rvaporation. This can be done if the Sn& is oxidized first with Br. Ordinarily, evaporatioh is not required except when zloPb is to be determined by 210Poingrowth. ~ E C O S T A h l I N A T I O N OF GLASSWARE. Compared to most other radionuclides, 210Pois difficult to remove from glassware. Chromic-sulfuric acid is suitVOL. 38, NO. 7, JUNE 1966
* 901
able for cleaning filter funnels between samples which do not vary in 210Po content by more than a factor of ten. Glassware and Teflon beakers are cleaned as follows: Arrange the items in a drainable position in a 4-liter
covered beaker; use two desiccator plates with feet as supports. Use perforated beakers for rods and other small items. Add concentrated "0s until its level is about 5 mm. below the bottom plate. Boil vigorously until
Table I. Variations in and Reproducibilities o f Mounting Techniques
Set no.
KO.of Source, treatment, and conditions replicates (Weightless) 4 I. 21oPo solution, weightless, evap. on planchets, well-centered. 4 11. 21oPo solution (50-X), weightless, evap. on planchets, well-centered. 4 111. Same treatment as 11. 4 IV. 2loPb zlOBi ZlOPo solution, weightless, evap. on planchets, well-centered. 4 V. 21oPo solution, weightless, evap. on planchets, not well-centered. (Ponderable: recommended method) 4 VI. ZlOPo separated from zloPb 210Bi ZlOPo solution by double precipitation, mounted as directed in procedure. 4 VII. 2laPo solution (standards), twice precipitated, mounted as directed in prbcedure. 4 VIII. Same treatment as S711. 4 IX. Same treatment as VII. (Ponderable: miscellaneous) 4 X. ZlOPo solution 1 mg. Te (in soln.) evap. on planchets, not wellcentered. 4 XI. *laPo solution, through entire procedure, filtered through fritted elass. Te dissolved and evap. on Elanihets, not well-centered-. 3 XII. Same treatment as XI, but used Se instead of Te, Se removed with HBr, not well-centered. u for an individual counting.
+
+
+
+
+
Average deviation from Range of Counting mean deviations
70
%
7c
1.0
0.5
0.4-0.6
0.3
1.0
0.2-1.8
0.3 0.4
2.6 2.1
2.0-3.3 0.5-4.2
1.0
8.6
7.5-9.6
0.3
0.9
0.1-1.6
1.o
1.6
0.6-3.1
0.2 0.07
0.3 0.8
0.2-0.5 0.2-1.7
1.0
2.6
2.0-3.2
1.2
5.3
1.6-9.0
1.1
1.1
0.8-1.7
ua
Recoveiy o f Polonium-210 from Standards and from W a t e r Samples b y Recommended and Short-Cut Methods
Table II.
Polonium-210 added pc./l.
Approx. u of counting %
0.000
10
0.056
20
0.186
6
1.86
2
18.6
0.6
163.6
0.2
1636
0.07
Recovery of polonium-210, % Water samples Precipitated Recommended Short-cut standards method method (0,050 pc./l.) (0.056 pc./l.) (0.132 pc./l.) (0.035 pc./l.) (0.033 pc./l.) (0.132 Pc./l.) 92.9 94.6 99.5 96.8 101.6 100.0 98.9 101.1 99.4 99.2 99.6 99.8
78.6 98.6 101.1 93.5 102,7 104.8 100.0 99.5 101.1 99.6
99.0 101.8 99.9 100.0
97.5 99.7
100.1" 98.8 Weighted av. n Standardization of solution included other solutions not shown here. b Boric and hydrofluoric acids not added.
902
ANALYTICAL CHEMISTRY
122.1 107.9 109.3 102,5 101.9 103.1 100.0 100.6 94.8 99.8 100.4b 99. 6b 97.4b 97. 97.2 95.4 101. 5b 100.3b 99.9b 98. 5b 98.8
the vapors condense freely on the items and the cover glass. Cool 15 to 20 minutes. Repeat twice. Remove and rinse items. TESTS, RESULTS, A N D DISCUSSION
M o u n t i n g and Counting. A number of mounting techniques were investigated. T h e techniques and results are outlined in Table I. Mounting the zloPowith T e on a membrane filter results in a reproducibility which compares favorably with the technique of evaporation of carrier-free 210Po solution. Although no information on selfabsorption is given in the table, this was a serious factor in Sets X, XI, and XII. Hence, despite the reproducibility indicated for Set XII, the technique was not considered to be as good as that used in the recommended method. The fractions of samples obtained in the experimental work can be placed in three categories: (a) the main T e precipitate containing the major portion of the 210Po;(b) the T e precipitate containing the 210Po recovered from filtrates; and (c) the T e precipitate containing the 210Porecovered from the glassware used in the final precipitation and filtration of the main Te precipitate. The main precipitates were counted a t least 24 hours no matter what their activities were; precipitates from the other two categories usually were counted 24 hours, but in some cases shorter counting periods were used. Repeated countings with the same planchet-counter combinations showed that other factors affected the high count rates much more than the counting statistics did. A t the higher activitie:, results have been roundkd to four digits; this procedure is justified by the statistics of counting but not by the absolute accuracy of the standardization of the 210Posolu'cions. Analyses of Samples Containing Added Polonium 210. Known
-
amounts of 210Powere added, as indicated in Table 11, to replicate aliquots of the water sample of the chemical composition shown in Table I11 and the resulting solutions were analyzed by the recommended and short-cut methods. Duplicate portions of the standard 210Posolutions were doubly precipitated, mounted, and counted. The water originally contained less than 0.02 pc. of 210Poper liter. As judged by the weighted averages, the recoveries from samples are 98.8y0 by both methods and are 1.3y0less than the average of the standards. To within the experimental error, the reproducibilities of the two methods and the standards are equal. Losses. Obviously, some self-absorption losses occur with samples and standards because of t h e mass of t h e counted precipitate. Comparison of t h e standards and samples in Table I1 indicates t h a t t h e average additional
self-absorption loss for samples is not more t h a n 1.3%. Standards containing 0, 1, and 10 mg. of Bi or Pb, or both, were carried through single and double precipitations to determine the effect of varying the amount of these carriers. The effect was very slight (I., April 1955. (6) Figgins, P. E . (Ed.), “The Radiochemistry of Polonium,” A’AS-‘YS Kept. 3037, OTS, Department of Commerce, Washington, I>. C., 1961. (7) Fink, It. M. (Ed.), “Biological Studies
with Polonium, Radium, and Plutonium,” 1Yh:ES VI-3, McGraw-Hill, New York, N. Y., 1950. (8) Frisch, & Feldman, I., I., “A Note on Precision Plating of Polonium,” Univ. of Rochester At. Energy Project Rept.
UR-426, Rochester, ?J. Y., February
1956. (9) National Bureau of Standards, “hlaximum Permissible Body Burdens and Maximum Permissible Concentrations of Radionuclides in Air and in FVater for Occupational Exposure,” Handbook 69, Washington, D. C., June 5, 1959. (10) Itundo, J., “The Analysis of Biological Samples for Polonium,” AERE HP/R-627, Harwell, England, 1950. (11) Rushing, D. E., Garcia, W. J., Clark, D: A., “The Analysis of Effluents and Environmental Samples from Uranium hIills and of Biological Samples for Radium, Polonium, and Uranium,” Radiological Health and Safety in hlining and Milling of Suclear hlaterials, Vol. 11, pp. 187-230, Intern.
-4t. Energy Agency, Vienna, Austria,
1964. (12) Scott, R. G., Stannard, J. N., “Modified Procedure for Analysis of Polonium-210 In Biological llaterial-,”
Cnav. of IZochester At. Energy Project Rept. UR-235, Rochester, N. Y., llarch
1953 (13) Smith, F. -4,Della Roha, R J., Casarett, L J , “Analytical and Autoradiographic Methods for Polonium210,” Unzv. o j Rochester At. Energy Project Rept. UR-305, Rochester, N. Y., November 1955. RECEIVEDfor review December 1, 1965. Accepted March 28, 1966. Mention of trade names is not to be construed as endorsement of the products by the Federal Water Pollution Control Administration.
Liquid-Liquid Extraction of Anionic Americium and Europium Complexes of Hyd roxyethy lethy1e ned ia minetriacetic Acid and Diethylenetriaminepentaacetic Acid SIR: A number of new liquid-liquid extraction systems ( 2 ) were recently described, based on the power of various high-molecular-weight ainines t o extract anionic chelate complexes of many metal ions from aqueous solutions of most organic acids. Several EDTAamine systems were among the more interesting ones considered to have great potential in separations chemistry. T h e writer now reports that the anionic chelate complexes of americium and europium with X-hydroxyethylethylericdiaminetriacetic acid (HEDTA) arid diethylenetriaminepentaacetic acid (IITPA) exhibit similar extractability. Interestingly, these very large anions w r e previously thought’ to be inext’actable. Unlike the E D T A complexes, the DTPA complexes do not sorb readily on anion exchange resins ( I ) ; no work has been reported for the anion resin behavior of the H E D T A complexes.
a quaternary ammonium chloride available from General Mills, Inc., Kankakee, Ill. The 20% (w./v.) Xliquat 336-S-C1xylene was prepared by dissolving 200 grams of Aliquat 336-S in 1 liter of reagent arade xvlene. It was then stored in glass bbttle. The 20% illiquat 336-S-DTPA-xylene was prepared by mixing 20y0 Aliquat 336-S-C1-xylene for 2 minutes with a n equal volume portion of O . 1 X NaSDTPX. The aqueous phase was discarded, and the treatment was repeated twice. The organic solution was centrifuged for several minutes and
a
Table I.
then decanted into a glass bottle for storage. T h e 20y0 Aliquat 336-S-HEDTAxylene was prepared by mixing 20y0 Aliquat 336-S-C1-xylene for 2 minutes with an equal volume portion of 0.3M NaSHEDTA. The aqueous phase was discarded and the treatment was repeated twice. The organic solution was centrifuged for several minutes and then decanted into a glass bottle for storage. Diethylenetriaminepentaacetic acid pentasodium salt (Sa5DTPA) and N hydroxyethylethylenediaminetr i a c e t ic acid trisodium salt(NasHEDT.l) are
Liquid-Liquid Extraction of the HEDTA Complexes of 241Amand 1 5 2 - 4 E ~ Tracers with 20% Aliquat 336-S-Xylene Solution
Aqueous phase pH‘
Solvent 20% Aliquat
Tracer extracted, % 241Am lb2-4Eu
