Table I. Analyses of Synthetic Uranium Samples Uranium, mg/g Dichromate Coulometric Sample type Known value titration titration U-Zr-A1 5.74 5.74 5.76, 5.76 25.26 25,26 U-Zr 25.28, 25.26 3.82 U-Th 3.82 3.81, 3.82 Table 11. Analyses of Actual Production Samples
Uranium, g/g Dichromate titration ( N = 2) Coulometric titration 0,8770 0.8769 (N = 7) 0.8768 0.8759(N = 3) 0.2674 0,2676, 0.2679 0.2716 0.2719, 0.2719 0.2674 0.2673(N = 3) 0.2716 0.2720(N = 4) 0.2682 0.2679 (N = 3) 0.7475 0.7473, 0.7478 ~
Sample type
uoz U-Zr-Ca U-Zr-Ca-Si Ore concentrate ~
~~
~
dichromate and vanadate systems, 590 mV GS. 570 mV, respectively, similarities in the interferences are expected. Therefore, the effects of vanadium and manganese in the proposed procedure were studied briefly. Vanadium, as expected, gives positive errors. In the determination of 100 mg of uranium, theerror from 15 mg is +0.29%; from 20 mg, + 2 . 2 z ; from 25 mg, +3.8%. As in the conventional titration, vanadium is apparently reduced to V(II1) by the Fe(II), and the V(II1) is not completely oxidized to V(IV) during the oxidation of the excess Fe(I1). Manganese gives negative errors: up to -0.4% with 15 to 30 mg of manganese. As with the conventional titration, the effect of manganese is erratic and often seems to be inde-
pendent of the exact manganese concentration. This interference, apparently caused by the oxidation of manganese during the oxidation step to a valence state that oxidizes U(IV) or V(III), will be studied in future work. Although the proposed procedure has little to offer over the manual dichromate titration, for an automatic titration it presents the distinct advantages common to coulometric titrations of dispensing with the buret and preparation of the standard titrant, and substitution of the simpler time read-out for the volume read-out. It also offers a way of carrying out V(V) titrations for which no good primary standard vanadium pentoxide is available (3). Analysis of Samples. Weighed aliquots of a standard uranium solution prepared from New Brunswick Laboratory (NBL) standard uranium dingot metal (99.972% U) were analyzed. A series of nine determinations with 80 to 120 mg of uranium showed a relative standard deviation of 0.062% and a relative difference of -0.023 =t0.048% (95% confidence limits). The platinum-gauze generating anode was used for these analyses. Table I gives the results of standard uranium mixtures. These samples were also analyzed by the NBL dichromate procedure (2) which has been shown to give both a precision and accuracy of within 0.1 % for these sample types. Table I1 summarizes the results of actual production samples of various types together with results obtained by the NBL dichromate procedure. ACKNOWLEDGLMENT
The authors gratefully acknowledge the assistance of Ralph J. Hemmer of the Analytical Instrumentation Section in the design and fabrication of the coulometer. RECEIVED for review August 5,1971. Accepted September 21, 1971.
Radiochemical Separations with Halogenated Resins M. Heurtebise’ and W. J. Ross2 Departamento de Tecnologia Nuclear, Instituto Venezolano de Investigaciones Cientificas, Apartado 1827, Caracas, Venezuela A CONTINUING EFFORT is being carried out in this laboratory to make the inherent high sensitivity of neutron activation analysis available for routine determination of trace elements. When such analysis cannot be achieved by nondestructive gamma ray spectrometry, a n effective and simple radiochemical separation is required. Ion exchange chromatography has been successfully adapted to rapid separation methods that are readily automated (/, 2). Our interest in the determination of iodine in body fluids led also to the development of a rapid separation of this element by means of an “iodinated” resin (3). It has been shown that a n anion exchange resin To whom correspondence is to be sent. On leave from Oak Ridge National Laboratory P.O. Box X, Oak Ridge, Tenn. 37830. 2
Comar and C. Le Poec, International Conference on Modern Trends in Activation Analysis, IAEA, College Station, Texas, 1965. (2) M. Heurtebise, J. Rndioaml. Chem., 7, 227 (1971). (3) M. Heurtebise and W. J. Ross, ANAL.CHEM., 43, 1438 (1971).
(1) D.
596
ANALYTICAL CHEMISTRY, VOL. 44, NO. 3, MARCH 1972
saturated by a concentrated solution of 1-/12/1; loses its ion exchange properties and exhibits highly selective retention of iodide from biological fluids. Similarly, bromine and its complexes are also retained very strongly on anion resins (4). The simplicity of the separation procedure obtained for the determination of iodine has led us to a more thorough investigation of this type of resin. This work presents the use of “brominated” and “iodinated” resins for the radiochemical separations of Br-, I-, Hgz+, and Au3+from interfering radioisotopes produced by neutron activation of various matrices. The separation of *OBr and Ig7Hg from activated urine samples is described as examples of the use of these resins. EXPERIMENTAL Preparation and Use of the “Halogenated” Resins. A resin bed approximately 1-cm high is prepared by packing 150 mg of dry Dowex 2 X 8 (200-400 mesh) in a polyethylene tube shaped like a medicine dropper. The resin bed is ap(4) M. Ziebler, Arrgerv. Clrern., 8, 283 (1959).
Element 38~1-
82Br1311-
3sS04a75Se04232P04s?eAs(V) z4Na+
ZK+
4
86Rb+ i a ~ +
Z?MgZ+ 45Ca2+ 87mSr 2+ l39Ba2+ 1 l0mAgi 56Mn2’ 80Co2+ 6SNi2+ 64CuZ+ 69mZn2+ 115CdZ+ 203HgZi 124sb(111) 108Au31
Table I. Retention of Ions on Halogenated Resins Brominated resin Iodinated resin Retained Number of 1-ml Retained Number of 1-ml on resin, z5 washings require@ on resin, washings requiredb 3 3c 20 3 99.5 ... 99.8 ... 6Y 20 -
4 3 3 4 3 3
95
...
-
-
98
-
99
59Fe3f
-
28.413’
-
6lCr3f
140La3+ 62V(V) 238u(v1)
-
4 3 3 3
4 3 3 3 3 3
4 4
86 -
-
...
97
...
98
3
3 4 4 3 3 3
-
Conditions
4 4 4 4 4 4 3 3 4 3 5
3
... 3 3 4 3 4 4
... 4
...
-
4
-
3 3 4 4 3
PH 5 PH 3
IHFI = 1 0 - 1 ~ AuHC14, HzO pH 2 . 5 pH 3 . 5 PH 5
PH 3 Absence indicates no measurable activity above background detected on the resin. Number of water washings required to obtain complete elution. Absence of value indicates washing does not affect the % retained on the resin. Per cent retained after 20 washings. a
proximately 1 cm high. The resin is washed slowly with a n iodine-iodide or a bromine-bromide solution until no difference can be observed between the color of the influent and effluent. An additional volume of 10 ml of reagent is passed through to ensure complete saturation. After preparation, the resins are stored in the proper halogen-halide solution. The iodine-iodide solution contains 25 grams of iodine in 1liter of 1 M K I and the bromine-bromide solution is prepared by dissolving 20 ml of bromine in 1 liter of 1 M NH4Br. Prior to use the resin colums were washed with 1 or 2 ml of water. Aqueous solutions containing 1 mg/ml of the selected elements that had been irradiated in the RV-1 reactor were passed through the resins at a flow rate of 1 to 4 ml/min. In certain cases, solutions which had been “spiked” with adequate radioactive tracers, were employed in place of activated elements. After complete passage of the samples, the columns were washed with successive 1-ml volumes of water. The degree of separation achieved with each element was determined by measuring the activity of each eluate and the residual activity in the resin column. Additional experiments were performed with solutions of Br-, I-, Hgz+, Au3+,and Ag+ to establish the effects of varying different concentration and pH, Procedure for Separationof *OBr or Ig7Hgin Irradiated Urines. In the case of bromine analyses 0.1 ml of urine that has been diluted with 0.9 ml of water, was encapsulated in a polyethylene tube and irradiated for 20 min a t a thermal neutron flux of -5 X 10l2n cm-2 sec-I. After irradiation the sample was transferred to a brominated resin column. The resin was subsequently washed with ten 1-ml portions of 5 NaCl solution. For mercury determinations, a sample of 2 ml of urine was encapsulated in a quartz tube and irradiated for seven hours in the same conditions. After a decay period of 12
z
hours, the sample was transferred to a n iodinated resin column. Then the resin was washed ten times with 2-ml portions of 10 NaBr solution. The resin was removed from the tube and placed inside of a plastic disposable beaker of 0.04-mm thickness and 20-mm diameter. The gamma activities of 17.6 min 80Br and 64.14 hr 197Hg were respectively determined by means of 3-in. X 3-in. and thin NaI(T1) detectors. The latter consists of a crystal 2 inches in diameter and ‘1s inch in thickness which is sandwiched between a 0.005inch beryllium window and a 2-inch diameter, ‘is-inch thick quartz light pipe. A 400 multichannel analyzer was used with both detectors. RESULTS AND DISCUSSION
Retention Studies. Table I shows the results of the separation achieved when solutions of 31 selected ions were passed through the halogenated resin columns. These ions were selected since they appear in a great number of matrices and are elements which usually present interferences in activation analysis. The total amount of each ion passed was 1 mg. It can be observed that on iodinated resins, I-, Hgz+, and Au3+are almost completely retained on the resin while Ag+ is retained up to 95 %. The remaining ions can be eluted with three to four 1-ml washings of water. Washing does not alter greatly the per cent retained of I-, Hg2+,Au3+,and Ag+. Brominated resins show a slightly different behavior. In this system Br-, Hg2+, and Au3+ are almost completely retained on the resin while about 1 4 z of Ag+ can be eluted. The retention of Ag+ is not reproducible on either type of resin and a precipitate of the silver halide is obtained in the effluent. ANALYTICAL CHEMISTRY, VOL. 44, NO. 3, MARCH 1972
597
0
40-
M
30-
b
Figure 1. Elution curve of iodide on brominated resin
2
2 1
L1
20-
IO-
'';;;45
c
I\
2b
4b
25 40 35 Number of I m i w c s h i n g
a
4'5
53
55
60
65
70
'"
0 51 I Mev(80Br) P,
Ib
O 6 F M e v (80Br)
Figure 2. ?-Ray spectrum of brominated resin after passage of irradiated urine sample Irradiation time, 20 min; decay time, 10 min; counting time, 1 min; flux = 5.9 X lo1*n ern+ sec-l
Energy, Mev It can also be observed that I- and C1- ions fixed on brominated resin can be eluted slowly by increasing the number of 1-ml washings. The per cent of I- contained in each 1-ml washing is shown in Figure 1. It is observed that the amount of I- eliminated by each wash decreases asymptotically. A similar curve is obtained for C1- ion and after passing twenty 1-ml washings, the per cent C1- retained is only 3%. These types of elution curves are different from those normally obtained in ion exchange and indicate that these halogen treated resins have a different exchange mechanism than those of untreated resins. The retention of I- on iodinated resins, Br- on brominated resins, and Hg2+, Au3+, and Ag+ o n both resins was studied as a function of p H in the range between 1 and 7. The amount of these ions retained on the resin is independent of pH. However, in the case of iodinated resins, when a 12 N HNO, solution containing 1 mg Hg2+jml is passed through, only 91 % of the Hg is retained and copious quantities of io598
ANALYTICAL CHEMISTRY, VOL. 44, NO. 3, M A R C H 1972
dine escape the resin. This liberation of iodine is due to the oxidation of the iodine complexes that are fixed on the resin and indicates that the resin is deteriorating. Brominated resins are not affected by strong H N 0 3 solutions. The resins cannot be used under basic conditions since at a pH 7.5 for bromide and 9.5 for iodine, the halogens decompose to form the unstable hypobromite and hypoiodite species, respectively. For this reason, I- is not quanlitatively fixed on an iodinated resin when the p H is higher than 9.5 (3). The use of reducing and oxidizing agents which can modify the halogen species of the resins can lead t o erroneous results. The retention of Br-, I-, Au3+, and Hg2+was also studied as a function of the concentration of these ions. The total amounts passed of these ions was varied between 200 ng and 2 mg and tracers were used. Carrier-free solutions of l3II were also used. The results revealed that the retention of these ions is independent of the concentration in this range. Thus il is not necessary to add carriers to such dilute samples.
197 Hg P *:‘ 68 KeV K-x ray t 77 K e V y r o y @
e
.$
Figure 3. Low energy -,-ray spectrum of iodinated resin after passage of irradiated urine sample Irradiation time, 7 hours; decay time, 28 hours; counting time, 20 min; flux = 5.9 X 10l2n c n r 2 sec-I P
%
Iu u
cuu
Channel number Reproducible retention of Ag’ can be achieved only when its concentration is less than 1 pgiml. Under this condition, retention of Ag- is 98 % and 94% on iodinated and brominated resins, respectively. Applications. The selective retention of these brominated resins can be applied to the determination of bromine in activated urine samples since 80Bris retained while the other radioactive constituents (primarily W I and *“a) pass through the column. Through the use of s2Br radiotracer it was observed that only 96% of the bromine in urine (usually 5-20 ppm) was retained if 0.1-ml samples were passed through the columns. However, the retention was decreased when larger volumes of urine were analyzed-for example only 91 % retention was achieved with 1-ml samples of urine. Increasing the resin quantity does not allow the use of larger urine volumes. This effect is not understood at present; however, a 0.1-ml sample is sufficient to achieve adequate sensitivity of bromine after a n irradiation of 20 min a t a flux of 5 X 10l2 n cm-* sec-l. Prior t o irradiation 0.9 ml of HzO is added to the 0.1-ml urine sample. The amount of 38Clretained by this resin, shown in Table I, can be reduced further and eluted more rapidly by using 5x NaCl as washing media instead of water. The improvement is probably due to the fact that the NaCl acts as an isotopic diluent for 38Cl. The NaCl has n o effect upon the retention of Br-. A spectrum obtained from a resin after irradiation and passage of a urine sample is shown in Figure 2 which indicates the 511 Kev annihilation and 620 Kev gamma transition which correspond t o 80Bras well as some W I contamination. Since iodinated resins retain Hg2+selectively, the use of this resin was investigated for isolating Hg from activated urines with the purpose of analyzing Hg. The irradiation and passage through the resin of 2 ml of urine revealed that traces of activated bromine, as 82Br, remain as contaminants o n the column and they are very difficult t o remove. However, washing the resins with 10% NaBr solutions decreases these traces of bromide ion to such a n extent that it allows accurate measurements of the 68-77 Kev peak of lg7Hgby using a thin NaI(T1) detector. When 203Hgwas used as a tracer, washing with 10% NaBr solutions does not elute the mercury. Figure
3 presents a spectrum of a n iodinated resin after fixation of 197Hgfrom 2 ml of irradiated urine which shows a peak a t 73 Kev as well as a peak at 30 Kev. The portion of the spectrum corresponding to the 73 Kev peak was compared with a pure sample of lg7Hg,and the two spectra were superimposable. The decay of this peak was also measured and it yielded a half life of 66.7 hours. These two experiments corroborate the presence of lg7Hgand that the 73 Kev peak is due t o the Ig7Hg. However, it can be seen from Table I that Ig8Aucan also be retained by the resin. 198Au produces an X-ray of 71 Kev which could overlap with the Ig7Hgpeak. With a 3-in. X 3-in. NaI(TI) detector, no peak appeared at 412 Kev, a fact which indicated the absence of lg8Au. The fixation of lg7Hgfrom irradiated urine permits the analysis of mercury in urine. CONCLUSIONS
Use of these halogenated resins permits simple and rapid separation of such ions as I-, Br-, Au3+, Hg2+, and Ag+ in neutron activation analysis. Since these resins require neither the presence of carriers nor constant flow rates, their use is amenable for routine applications. The resins can be reused if stored with the proper halogen reagent and if sufficient time is allowed for complete decay of the activated ions retained in the resin. Bromine and iodine can be determined even in the presence of Au, Hg, and Ag which are also selectively retained in the resin since it is possible t o select short irradiations and measure the short lived isotopes of Br and I. It has been calculated that lg7Hgcan be determined in the presence of Ig8Auif their relative concentrations are comparable. Ag interferes only if its concentration is 100 times greater than that of Hg or Au. ACKNOWLEDGMENT
The authors thank J. A. Lubkowitz for redacting the manuscript in English and for his critical comments. RECEIVED for review August 19, 1971. Accepted September 22,1971.
ANALYTICAL CHEMISTRY, VOL. 44, NO. 3, MARCH 1972
599
