Polarographic Determination of Lead in Americium Dioxide with Hydroxylamine Hydrochloride as Supporting Electrolyte SIR: The purity of americium dioxide has been determined a t Rocky Flats mainly by spectrographic analysis ( 1 , 4 ) . The reported lead concentrations in the Am02 have varied from a few parts per million to more than 2y0. The spectrochemical methods used have been most successful in determining the lead concentrations a t levels less than 1000 p.p.m. To determine higher concentrations of lead, a polarographic procedure has been developed. EXPERIMENTAL
was dissolved in less than 5 ml. of 0.3M HC1. Sufficient 5 M NHzOH.HC1 and 0.2% gelatin were added to make their concentration in the final solution 0.5M and 0.0174, respectively. The solution was diluted to volume with water and a portion was transferred to the electrolysis cell. Oxygen was removed by bubbling purified nitrogen through the solution for 15 minutes. Calibration Procedure. A calibra tion curve for lead was prepared by pipetting the proper aliquot of a standard stock solution into a 50-ml. volumetric flask. These solutions were analyzed in the same manner as the samples discussed above. Lead solut’ions of fifteen different concentrations were prepared ; four polarograms were recorded of each concentration. A plot of the lead concentration (C) us. diffusion current ( i d ) is linear for the range of the lead concentration from 0.003 to 10.00mJf. The extrapolated curve passes through the origin, and the average relative standard deviation of the diffusion current quotient ( 2 ) (id/C) was 2.04yG. This curve can be used for solutions prepared from Am02 because americium does not interfere. A plot of E d . $ . us. the log ( i / i d - i) for the standard lead solutions produces a straight line with a slope equal to 0.031 volt. This experiment,al value is in good agreement with the theoretical value of 0.030 volt for the reduction of a divalent metal ion. The half-wave potentials were measured according to the method recommended by Sargent ( 5 ) and were corrected for the cell I R drop. The half-wave potential determined for the reduction of P b + 2 to PbO was -0.448 =t0.004 volt us. S.C.E. Warren (6) reported a halfwave potential of -0.46 volt us. S.C.E. for the reduction of divalent lead in 2M NHzOH. HC1.
Apparatus. All polarograms were obtained using a calibrated Sargent Model XV recording polarograph. For the analysis of solutions of low lead concentrations (0.003 to 0.100mM), a Sargent Micro Range Extender was used as a n accessory. The electrolysis cell was a two-piece H-form cell which contained a S.C.E. A Sargent constant head dropping mercury electrode assembly was used. None of the measurements were damped. Safety Precautions. Because of the toxicity of americium, extreme care must be exercised in its handling. ,111 work with XmOn was performed in a glove box. The solutions containing americium were analyzed polarographically in a well-ventilated hood. The glove box and t h e open hood were lined with lead to protect the analysts from gamma radiation. -1dditional shielding was placed in front of the electrolysis cell while the polarograms were being recorded. Reagents. A11 reagents were analytical grade. Sample Preparation. T h e AmOz samples (100 to 150 mg.) were weighed directly into a tared volumetric flask ( 2 5 or 50 ml.). About 10 ml. of 6 M HC1 were added, followed by about DISCUSSION A N D RESULTS 3 ml. of 8.V H S O s . This mixture \\as warmed on a hot plate to dissolve Init’ially, IIH20H.HCl, in the same the AmOz and was subsequently concentration as suggested by Warren taken almost to dryness. The residue (6), was used as t’he supporting electrolyte. When the concentration of lead was less than 0.100mM, however, interference developed. Some preTable I. Recovery of Lead from liminary work indicates that this interUnknown Standard Solutions ference is probably from mercury. By P b f 2 ,Mg. Recovery of lou-ering the IIHzOH .HCl concentraPresent Found Pb+2,70 tion from 2 to 0.5M, this interference 0 . 5 2 Too dilute .,. was eliminated. 2.61 2.57 98.5 The gamma radiation from the 5.24 5.03 96.0 americium caused deterioration of the 99 4 10 46 10 40 25 69 98 4 26 11 agar when the salt bridge was exposed 101 2 157 1 158 9 daily to americium solutions. This 266 8 102 0 261 6 deterioration required the changing of 103 2 523 2 539 9 the salt bridge at least once a week. 102 0 1308 0 1334 0 2700 0 103 2 2616 0 Solutions prepared from hmOz were stable and unaffected by radiolytic deAv. 100 4270 composition products for about’ a week.
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ANALYTICAL CHEMISTRY
After that, the diffusion currents became erratic even though the shape of the polarograms remained unaffected. The reliability of the method was determined as follows: lead “unknown” solutions were prepared and analyzed; expected impurities were checked; and lead was determined in solutions of .Im02 that were spiked with known amounts of lead. Ten unknown solutions of lead were prepared and 25 ml. of each were transferred to a 50-ml. volumetric flask. These solutions were analyzed polarographically according to the previously described method. The relative error for nine of the unknown solutions was 0.427, (Table I) and the relative standard deviation of the per cent recovery was *2,49%. The tenth solution v, as too dilute to be analyzed polarographically. Standard lead solutions (2.0mM) were spiked separately with each of the following 10 cations a t the concentrations (mM) indicated: Cd-2, 0.201; Ce+4, 1.109; C U + ~0.400; , Sit2,0.399; Kb+j, 0.887; T h f 4 , 0.216; UOz+2, 0.400; Y+3, 0.202; Zn+*, 0.401; and Zr -t4, 0.441. Subsequent polarographic analysis indicated that none of these cations interfered in the formation of the lead wave. The relative error of all of these was 1.977, and the relative standard deviation of the per cent recovery was =t0.58%. I t is likely that the reduction of Sn+2 (Ellz = -0.48 volt vs. S.C.E.) (6) and TI+ (Ellz = -0.51 volt US. S.C.E.) ( 6 ) TVOuld seriously interfere with the determina-
Table II. Results of Polarographic Determination of Lead in Americium Dioxide Samples Pb results, wt. 7% Av. result 0.0110 0.0112 0.0104 0.0109 0 128 0.130 0.124 0.127 1.31 1.30 1.30 1.30 1.77 1.75 1.77 1.76 1.78 1.78 1.79 1.78 2.06 2.08 2.08 2.07
tion of Pb+*. Thallium is not usually found in dmOz, however, and t h e concentration of tin is too low to cause significant interference. I t could be predicted from the reduction potentials of Am+3 (3) that americium will not interfere with the determination of Pb+2. This absence of interference was found to be true even when the americium concentration was 10,000 times greater than that of lead. A polarogram was recorded for each of 32 AmOz solutions that contained lead spikes within the concentration range from 0.012 to 1.38mM. These solutions mere analyzed according to the sample preparation procedure. The
relative error was -0.23% with a range from 94.5 t o 104.0% and the relative standard deviation of the per cent recovery was f1.59%. The method developed was used t o analyze six AmOz samples for lead. The lead concentration ranged from 0.01 to 2.07y0. The relative standard deviation of the results over this concentration range varied from 3.82 to 0.45%. The data are given in Table 11. LITERATURE CITED
(1) Barton, H. N., Rocky Flats Division,
The Dow Chemical Company, unpublished data, 1964. (2) Kolthoff, I. M., Lingane, J. J.,
“Polarography,” 2nd ed., p. 377, Interscience, New York, 1952. ( 3 ) Penneman, R. A,, Asprey, L. B., Proc. Intern. Conf. Peaceful Uses At. Energy, Geneva, 1965, 7, 355 (1956). (4) Sandberg, R. A., Rocky Flats Division, l h e Daw Chemical Company, unpublished data, 1964. (5) Sargent, E. H. and Co., “Manual of Instruction for Sargent Model XXI Visible Recording Polarograph,” p. 19, Chicago, Ill. (6) Warren, C. G., U . S. A t . Energy Comm. Rept. LA-1843 (1953). C. E . PLOCK Chemistry Research and Development Laboratories Rocky Flats Division The Dow Chemical Co. Golden, Colo.
14-M.E.V. Neutron Activation Analysis of Rare Earth Elements in Ores and Minerals SIR: Nondestructive activation analysis of certain specific elements in various matrices using 14-m.e.v. neutrons gained importance in recent years with the availability of small neutron generators. This type of analysis will be particularly ‘useful for elements which form short-lived products upon reaction with 14-m.e.v. neutrons. The rare earth elements have been determined in geological samples in the past by activation analysis technique, but the particles employed in most of these analyses have been thermal neutrons ( 2 ) . When conventional methods or thermal neutron activation analytical techniques were used, chemical separations have been performed which are time-consuming. I n the present work, we have used the 14-m.e.v. neutron activation technique for a nondestructive and rapid analysis of ores and minerals for a few selected lanthanides. With a flus of about 3.0 X lo7 n/sq. cm.-second, cerium, praseodymium, and yttrium were measured with sensitivities of 300 pg., 150 pg., and 5000 p g . , respectively. A total of 100 c.p.m. under the photopeak after the subtraction of background was chosen to define the sensitivities reported here. .i large number of minerals obtained from different sources were analyzed for cerium, praseodymium, and yttrium using these techniques. EXPERIMENTAL
Nuclear Reactions Used for Measurement. T h e reactions which were employed for t h e measurement of the above elements are GelM (n, 2n) Pr141 (n, 2n)Pri40, and Y89(n,n’)Y89m, respectively. The respective cross sections for these reactions are reported as (1.2 f 0.4) barns, (2.1 f 0.3) barns
and (0.15 barn, fission neutrons) (‘7, 10). The half lives of the active and YEgm,reproducts Ce139m,P?, ported elsewhere ( 5 ) were redetermined and found to be 58.0 f 2.0 seconds, 3.3 f 0.2 minutes, and 16.5 f 1.5 seconds, respectively. Cerium-139m and YESrn emit gamma rays with respective energies of 0.74 m.e.v. and 0.91 m.e.v., while PrlM emits positrons whose 0.51 1-m.e.v. annihilation radiation is detectable. Rocedure. All samples were prepared by weighing appropriate
Table 1.
amounts of t h e minerals and the standards into small polyethylene vials which are then sealed and enclosed in outer polystyrene vials. Both the standards and the samples are then activated under identical conditions using a pneumatic transfer system. A 150-kv. Cockcroft-Walton accelerator which generated 14-m.e.v. neutrons by the H2(H3, %)He4reaction was used for activating the samples. The activated samples were then counted in a dual crystal arrangement in which two 3-inch X 3-inch NaI(T1)
Analyses of Various Minerals for Cerium, Praseodymium, and Yttrium by 14-m.e.v. Neutron Activation
Catalog No. None None
Ce content, Pr content, Y content, Sample crg./mg. ,ug./mg. rg./mg. Monazitea 225 4~ 11 (3) 3 1 . 6 f 6 . 6 (3) Gadoliniteb 126 f 3 (2) 1 6 . 1 f 0 . 6 (2) (Baringer Hill), Buchanan, Texas None Gadoliniteb 2 6 . 2 f 0 . 4 (2) 6 . 4 f 0 . 8 (2) 194 f 10 (4) (Petnick quarry), Buchanan, Texas Samarskitec, 4 . 1 f 0 . 5 (3) 83147 56.4 f 3 . 6 (4) North Carolina Samarskitec, 89107 1 . 6 ==! 0 . 4 (3) 73.0 f 3 . 3 (4) India Samarskitec, 5 . 9 f 0 . 9 (4) 96115 ... 39.0 f 5 . 8 (5) New Mexico R13778 3 . 1 f 1 . 6 (3) .. Samarskitec, 5 8 . 5 f 3 . 8 (4) Brazil 103601 Allanitec, 103 f 14 ( 3 ) 1 1 . 8 f 1 . 3 (4) Texas Allanitec, 104353 99 f 10 (3) 8 . 1 f 0 . 8 (3) ... New York R7144 Euxenitec, 7 . 2 f 1 . 2 (3) , . . 114.8 f 9 . 2 (4) Norway R13768 Euxenitec, 4 . 4 f 0 . 4 (3) ... 20.8 f 3 . 9 (4) North Carolina R8192 Fergusonite: 1 . 5 f 0 . 2 (3) ... 23.2 f 3 . 2 (4) Montana Fergusonite: R11543 2 . 5 f 0 . 4 (2) ... 234 f 12 ( 5 ) Norway Supplied by H. R. Blank of Geology Dept., Texas A & M University. Supplied by R. E. Zartman, U. S. Geological Survey, N.B.S., Washington, D. C. Supplied by P. E. Uesautels, Associate Curator, Division of Mineralogy, Smithsonian Institution, Washington, D. C.
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