was not attainable with a reasonable electrode spacing (Table V). Table VI shows that under optimum operating conditions the quantitative deposition of plutonium was reached in 15 minutes. The table also illustrates the substantial effect of a small quantity of iron upon the deposition rate.
Table VI. Electrodeposition Rate of Plutonium and Effect of Iron upon Rate (Current, 2.5 amp.; 0.4M NHIC1; electrode spacing 0.4 mm.; 0.75N HCI)
Plutonium Recovered, % Iron 0.5-mg. abaent iron
Time, Minutes
RESULTS AND DISCUSSION
The recovery of plutonium from urine by this procedure for ten determinations was 91.3 i 5.001, (Table VII). The analysis time was 5 to 6 hours and six samples were handled simultaneously with ease. The extent to which other alpha emitters follow the procedure was determined. The nuclides studied were J Pa231, and Np23’ and these Th232> UZ38 elements were carried through the procedure to the extent of 0.5, 2.3, 24.1, and 85.2%, respectively. Should an interfering alpha-emitter be present, the accurate quantitative assay of plutonium is still possible since the electrodeposited element is free of weighable residue and, therefore, amenable to alpha-ray pulse height analysis. Information concerning the chemical state of urinary-excreted plutonium is unavailable. The possibility existed that plutonium was organically bound and consequently unable to cocrystallize with rhodizonate. Therefore, it was essential to validate the initial separation step with authentically metabolized pliitonium.
20 Table VII.
94.3
were substituted for the cocrystallization step, (Ten determinations of plutonium added to 500-ml. volumes of control urine gave an average recovery of 93.7 f 5.0% by this modified method.) Plutonium assay of the urine from the exposed individual was 7.2 + 0.4 d.p.m. per liter by both methods. Clearly, metabolized plutonium combined with rhodizonate; therefore, the method is valid for the determination of this element in urine.
Recovery of Plutonium-239 from Urine
Number Plutonium Plytoof Recovered Urine nium Deter- and Standard Volume, Added, mina- Deviation, M1. D.P.M. tions %
In this regard urine obtained from an individual with known exposure to plutonium was analyzed by the procedure described as well as by a modified method which was designed to remove organic matter prior to plutonium isolation. The modified method was essentially the same as the one detailed except that evaporation of the urine to dryness and removal of the organic residue by asking a t 500” C.
LITERATURE CITED
(1) “Maximum Permissible Amounts of
Radioisotopes in the Human Body and Maximum Permissible Concentrations in Air and Water,” Handbook 52, U. S. Department of Commerce, Nat’l. Bur. Standards. 1953. (2) Mitchell, R. ’F., ANAL. CHEM. 32, 326 (1960). (3) Nelson, F., Rush, R., Kraus, K. h., 131st Meeting, - ACS, Miami, Fla., April 1957. (4) Sanders, S. hl., E. I. du Pont de Nemours & Co., Inc., Rept. DP-146 (March 1956). (5) Schwendiman, L. C., Healy, J. R., Reid, D. L., U. S. Atomic Energy Comm.. Rept. HW 22680 (November 1951). ‘ (6) Weiss, H. V., h i , M. G., ANAL. CHEM.32,475 (1960). (7) Wish, L., Zbid., 31,326 (1959). (8) Wish, L., Nucleonics 14, 102 (1956). (9) Wish, L., Rowell, M., U. S. Naval
Radiological Defense Laboratory, Rept. USNRDL-TR-117 (October 1956).
RECEIVEDfor review August 8, 1960. Accepted October 24, 1960.
Radiochemical Determination of Radium in Urine HERBERT V. WEISS and MlNG G. LA1 Chemicol Technology Division, U. S. Naval Radiological Defense laboratory, San Francisco, Calif.
b By experimentation with radium223 a rapid and accurate procedure was developed for the determination of minute quantities of radium in urine. The method depends upon the cocrystallization of radium from urine with potassium rhodizonate and the purification of this extract by ion exchange. Radium is isolated in an essentially residue-free form and its recovery from urine is 94.9 f 3.3%.
procedure is, therefore, below this limit. Several procedures with adequate sensitivity have been reported (3, 6). The method described here is comparably sensitive and has the advantages of carrier-free isolation, simple laboratory manipulations, and economy of operator time. EXPERIMENTAL
Potassium rhodizonate (Paul B. Elder Co., Bryan, Ohio). Tetrasodium (ethylenedinitri1o)tetraacetate (EDTA) (Bersworth Chemical Co., Framingham, Mass.). Ammonium chloride, reagent grade; solution prepared to contain 0.2 gram per milliliter. All other chemicals were either of reagent grade or c. P. quality. Reagents.
T
HE
RECOMMENDED
RADIOLOGICAL
safety control practice for monitoring exposure to radium is urinary assay. Hursh (4) calculated that an upper level of 2 X curie of radium per 24-hour urine sample is not to be consistently exceeded. The sensitivity requirement for a practical analytical
Radioactivities and Their MeasureRadium-223 was used in the ment.
experimental phase of this study because i t affords the convenience of gamma photon counting without interference from daughter products. This radionuclide was separated from actinium-227 by a solvent extraction procedure ( 2 ) . The purity of separation was established by decay measurements. Measurements were made in a well-type gamma scintillation counter. A radium-226 standard solution was obtained from the National Bureau of Standards. This solution was diluted as required, and used in the final proof of the procedure. Measurements were made in a gas flow alpha proportional counter a minimum of 4 hours after the deposition of radium on a platinum disk. Correction for growth of the alpha-emitting daughters was applied by the following formula which was VOL 33, NO. 1, JANUARY 1961
39
Table I. Recovery of Ra-223 from 1 % Solution of Potassium Rhodizonate in Urine Using Ammonium Chloride as Crystallizing Agent
Ammonium Chloride, Ml. 0.05 0.35 0.75
e
Ra-223 Recovery,
%"
81.6
96.3 98.2 98.2 1.00 99.3 1.50 2.00 98.9 98.1 3.0 95.4 6.0 Statistical error of counting was 1%.
Table II. Cocrystallization of Radium with Potassium Rhodizonate from Urine of Different pH
Radium Recovered, PH
%"
4.0
0 99.0 loo.1
5.1 5.8
5
99.0 6.5 99.7 7.1 Statistical error of counting was 1%.
Table 111. Desorption of Radium from Column of AG 50-X8 Using Solutions of 0.7570 EDTA-1% Citric Acid at Different pH
Effluent Fraction Radium in Fraction, yo (40 vi./ Fraction) pH 5.1 pH 6.0 pH 6.5 1 n n 0 0 0 0 0
2 3 4
5
0 0.2 0.3 0.5
0.2
0.2 2.6 9.1
Table IV. Desorption of Calcium from Column of AG 50-X8 Using Solutions of 0.75% EDTA-1% Citric Acid at Different pH
Effluent Fraction (20 M1.j Fraction)
Calcium4 pH 4.5 pH 5.1
4 5 6 a
+
+
7
absent.
Calcium
- calcium
present,
derived empirically and determined to be consistent with that computed from the Bateman equation: N = 0.25
+ 0.75 (1 -
e-0.00891)
where N is the fraction of the equi40
ANALYTICAL CHEMISTRY
librium value and t is the time in hours after deposition. Then Radium-226 d.p.m. = measured c.p.m. 4 X N X counting efficiency Procedure. Based upon t h e experimental results, the following analytical procedure was developed : To a 24-hour urine collection or a suitable aliquot adjusted to p H 5 to 7, add solid potassium rhodizonate to make a final concentration of 1%. If necessary, warm the sample to solubilize the reagent. Cool to room temperature. Add slowly and u-ith stirring the equivalent of 15 ml. of the ammonium chloride reagent per 100 ml. of sample. Let stand 5 minutes and separate the crystals by filtration. Dissolve crystallized rhodizonate in 20 ml. of 4N nitric acid and dilute to 200 ml. Pass this solution through the column. [The resin bed consists of a cation exchange resin of 50- to 100-mesh AG 50-X8 (Bio-Rad Laboratories, Berkeley, Calif.) in the H + form in a glass column 10 em. long and 0.6 cm. in inside diameter. The flow rate is 2 to 4 ml. per minute.] Wash with 50 nil. of mater followed by 100 ml. of an EDTA-citric acid solution, p H 5.1. (To 100 ml. of 7.5% EDTA, add 10.93 grams of citric acid monohydrate, dilute to 1 liter with distilled water, and adjust the p H to 5.1 with 6 N sodium hydroxide.) Wash the column with 100 ml. of 0.2N nitric acid and elute the radium with 100 ml. of 4 N nitric acid. Evaporate the eluate to dryness and ash the residue over a flame. Wash the walls of the ashing vessel with about 5 ml. of concentrated nitric acid and reduce the volume to about 1ml. Transfer the solution to a platinum disk (2.1-em. diameter) and dry on a hot plate. Flame the dried disk for 30 seconds. Count a minimum of 4 hours after flaming and correct the counting data for daughter growth. Cocrystallization of Radium from Urine with Potassium Rhodizonate. Radium cocrystallizes quantitatively with potassium rhodizonate from aqueous solution (6). The recovery of radium upon crystallization of rhodizonate from urine was studied. T o 10 ml. of urine with radium-223 tracer mas added 100 mg. of solid potassium rhodizonate. After complete solubilization, ammonium chloride solution was added slowly with vigorous stirring t o crystallize the rhodizonate. Vpon standing for 5 minutes, the crystals were separated by filtration, dissolved in nitric acid t o a definite volume, and gamma counted. The recovery of radium was determined by comparison with a standard diluted t o the same volume. The relation of radium recovery t o the quantity of crystallizing agent used is shown in Table I. When 0.75 t o 3.0 ml. of ammonium chloride solution are added the recovery of radium is essentially quantitative. As previously observed (6),with the use of
greater than optimum amounts of crystallizing agent, the recovery is diminished. Under optimum crystallizing conditions, the effect of acid concentration upon the recovery of radium from urine is shown in Table 11. Rhodizonate is uncrystallizable from urine adjusted to p H 4.0 and lower. From pH 5 to 7 the recovery of radium is quantitative. More alkaline conditions were not studied since under such conditions substantial quantities of substances nhich interfere with subsequent operations precipitate from urine. Purification of Radium Cocrystallized from Urine. Calcium, a normal constituent of urine (about 200 mg. per liter), also cocrystallizes with rhodizonate. The presence of this element interferes with the measuiement of radium by virtue of its mass, alpha particles being readily absorbed and scattered by solid matter. This source of interference n as eliminated by an ion exchange separation. I n a solution of EDTA-citric acid a t controlled pH, calcium may be preferentially chelated over strontium and barium ( 1 ) . Presumablj this difference in chelatability also extends to radium. This property serves as a basis for the separation of these elements, since under appropriate conditions the alkaline earth elements adsorb on cationic exchange resins n hile their chelated counterparts are nonadsorbable. Column conditions which permit the separation of radium from calcium were studied. A bed of cation exchange resin 50- to 100-mesh, AG 50-X8 in the H + form was prepared in a glass column 10 em. long and 0.6 em. in inside diameter. The flow rate for all solutions was 2 to 4 ml. per minute. An experiment v a s designed to determine the minimum pH a t \T hich radium u-as firmly adsorbed to the cation exchange resin in a buffer solution of 0.75% EDTA-l% citric acid. Radium tracer contained in 1 nil. of the buffer solution of p H 5.1, 6.0, or 6.5 was placed on a column previously washed with a solution of the same pH. The column was then washed with 200 ml. of the buffer solution and measurements for radium activity were taken for each 40ml. fraction of effluent. At p H 5.1 radium was not detected in the effluent while 1.0 and 12.1% of the radium were eluted from the columns washed with p H 6.0 and 6.5 buffer, respectively (Table 111) The desorption of calcium from the resin column was also determined with EDTA-citric acid solutions of different pH. Five milliliters of a neutral solution which contained 11 mg. of calcium per milliliter were placed on the column. The column was then washed with 140 ml. of a buffer solution of p H 4.5 or 5.1. The presence of calcium in each 20 ml. of effluent was qualitatively determined by precipitation with oxalic acid. With the EDTA-citric acid solution of p H I
4.5, calcium did not appear in tlic effluent until more than 120 ml. passed through the column (Table IV). At p H 5.1 calcium ITas completely eluted with the 20- t o 100-ml. fraction of effluent. Following the separation of radium from calcium on the column the resin requires washing to remove residual EDTA and citric acid. The ability of 21% 0.' nitric acid to wash these agents from the column and the influence of this acid concentration upon radium desorption was examined. Radium tracer contained in EDTAcitric acid a t p H 5.1 was placed on a column. The column was washed with the dilute nitric acid and the radium and solid content were determined for each 40 ml. of effluent. Only O.lyoof the radium was lost after treatment of the column rr-ith 120 ml. of acid. Solids were not apparent in the evaporated effluent' be?-ond the first 40-mi. fraction. After washing the column free of interfering solids, radium is eluted. The volume of 4 X nitric acid required for complete elution was established a t a flow rate of 2 to 3 ml. per minute. One milliliter of radium tracer in dilute acid was fed onto a column previously washed with 0.2N nitric acid. Radium was completely desorbed from the column with 80 ml. of the elution solution (Table V).
Table V. Elution of Radium from Column of Ag 50-X8 Using 4N Nitric Acid
Fraction
of Eluate
72.8 24.0 3.2 1.0 0.0
6 X to 1.5 X curie of radium-226 were analyzed by this procedure. The results are shonn in
Table VI.
Recovery of Radium From Urine
Sum- Average ber Radium Average of ReDeviaRadium Added, Sam- covered, tion, Curie des 7% % 6 . 0 X lo-'*
3 . 0 x 10-11 3 . 0 x 10-10 1 . 5 x 10-9
RESULTS
Eleven samples of urine, 200 ml. in volume. to which were added from
Radium in Fraction, 70
(20 l\Il./Fraction)
0
2
3
2 4
93.9 92.1 95.0 97.1
Av. 9 4 . 0
2.3 1.5 0.4
3.0 3.3"
Standard deviation.
Table VI. The average recovery was 94,9y0 with a standard deviation of 3.3%. By tracing a i t h radium-223, the loss was determined to occur primarily in the evaporation steps. The final residue weight ranges from 0.2 to 0.5 mg. With residue weights of this magnitude, errors due to selfabsorption are negligible. Further if desired, this condition permits positive identification by pulse height analysis since the mass is insufficient for attenuation of the alpha particles. In this connection, examination of the extent to which other alpha-emitters follow the procedure indicated that uranium and plutonium were completely discriminated against while about 20% of both thorium and protactinium was recovered. LITERATURE CITED
S.Atomic Energy Comm.., Re& ORNL-1932 (September 1955). (2) Hagemann, F., J . Am. Ch,em. SOC. 72,768 (1950). (3) Harley, J. H., Foti, S., A'ucleonics 10, No. 2,45 (1952). (4) Hursh, J. B., University of Rochester, Rept. UR-522(A ril 1958). (5) Russell, E. R., Eesco, R. C., Schubert, J., Nycleonics 7;No. 1, 60 (1950). (6) Weiss, H. V., Lai, 51. G., ANAL. CHEM.32,475 (1960). (1) Farabee, L. B., U.
RECEIVEDfor review August 8, 1960. bccepted October 24, 1960.
X-Ray Rayleigh Scattering Method for Determination of Uranium in Solution J. C. McCUE, 1. L. BIRD, C. A. ZIEGLER, and J. J. O'CONNOR Tracerlab Inc., Waltham, Mass.
b A new x-ray technique has been applied for the quantitative determination o f a high Z material (uranium) in a low Z medium (dilute nitric acid). X-ray coherent, or Rayleigh, scattering i s employed to provide material specificity not obtainable with conventional x-ray analysis methods. This critical evaluation of the Rayleigh scattering technique for uranium determination supplements earlier limited experimenta tion.
T
measurement of high Z materials in a low Z medium by Rayleigh scattering techniques has been described ( 2 ) . A timely application is the quantitative determination of uranium in dilute nitric acid solution. Monochromatic absorptiometry has been HE
employed to perform much the same task ( I ) , but the sample requires substantially more premeasurement preparation to obtain equivalent accuracy. The detection of uranium in a low Z medium by Rayleigh scattering measurements is further enhanced by fluorescence of the uranium in the energy band yielding the Rayleigh signal increase (g, Figures 5 and 6). The composite phenomenon maintains detection specificity, and provides a considerable gain in net signal. Two solutions of dissolved reactor fuel elements n-ere analyzed in this work. One solution contained a n undetermined, but near-saturation, quantity of stainless steel compounds; the other was saturated with aluminum salts. Uranium was knomn t o exist in both solutions in small concentra-
tions, less than 1% by weight. The Z dependence of Rayleigh scattering permits measurement of the high Z component in concentrations small compared to low Z impurities-e.g.. aluminum, iron, nitrogen, oxygen, and hydrogen, Stringent accuracy requirements of less than il.Ogc v\-ere imposed. APPARATUS
Conventional x-ray generating equipment and detection instrumentation were utilized for these measurements. A schematic view of the apparatus used is shown in Figure 1 of (2). The only special equipment fabricated was an improved specimen holder incorporating irradiation and detection collimators in its design. This device, VOL. 33, NO. 1, JANUARY 1961
41
