stationary liquid which is a primary alkanol, a reasonable generalization of the results leads to the conclusion that the separation will be achieved on a stationary liquid which is a secondary alkanol, though otherwise of similar molecular structure. The figures for the two tertiary alkanols indicate that there is probably a similar differentiation between secondary and tertiary alkanol solutes on the two stationary liquids, though, with results for only two tertiary alkanols, the experimental evidence is not conclusive.
The results of Table I imply that the free energy of interaction of a secondary hydroxyl group with another secondary hydroxyl group or with a tertiary hydroxyl group is less than the free energy of interaction of a primary hydroxyl group with a secondary or tertiary hydroxyl group. id^^^^ that the interaction between secondary hydroxyl groups or between tertiary hydroxyl groups is less strong than that between primary hydroxyl groups Can be found in other ways-e.g., from infrared spectra (4),or from nuclear magnetic resonance spectra (3).
LITERATURE CITED
(1) Littlewood, A. B., ANAL. CHEM.36,
1441 (1964). (2) Littlewood, A. B., Willmott, F. W., ANAL.CHEM.38,1031. (1966). (3) Martin, M., J . Chzm. PhYs. 59, 736 (1962). (4) Smith, F. A., Creita, E. C., J . Res. Natl. Bur. Standards 46,145 (1951). A. B. LITTLEWOOD F. W. WILLMOTT University of Newcastle upon Tyne School of Chemistry, The University, Newcastle upon T ~1, ~ ~ , England
Emission Spectrographic Determination of Plutonium, Thorium, and Rare Earths in Americium Following Anion Exchange Separation SIR: Americium is a by-product of plutonium processing since americium241 is formed by the beta decay of plutonium-241, During chemical processing of plutonium, the accumulated americium may be separated and purified. Plutonium is one of the major impurities in americium obtained from this source. The rare earths, because of their chemical similarity to americium, follow it through most chemical separations and are of particular interest. The spectrographic determination of these elements in americium is complicated by the spectral complexity of the actinides and lanthanides, the scarcity of high purity americium, and the radioactivity of americium. Carrier distillation methods, routinely used for the analysis of impurities in uranium (8),plutonium (5, 7 ) , and americium (I), are not applicable to the detection of elements such BS plutonium, thorium, and rare earths because the refractory oxides of these elements are not volatilized from the base material during arcing of the sample. Ion exchange appeared to offer the best opportunity for a simple and quantitative separation prior to spectrographic determination. Plutonium and thorium have been separated from americium by adsorption of their anionic nitrate complexes onto an anion exRare earths change resin (4, 6). may be separated from americium by cation exchange in citrate solution (2) or by anion exchange in thiocyanate solution ( S , $ ) , EXPERIMENTAL
Gloveboxes used for handling americium had a '/*-inch lead sheet shield for personnel radiation protection. A spectrograph having a plate factor of approximately 2.5 A./ mm. is recommended. Reagents. Dowex 1, X-2, 100 to 200 mesh, chloride form resin (BioApparatus.
Rad Laboratories, Richmond, Calif.) was converted to the nitrate form and prepared in a column 0.85 cm. in diameter and 5 cm. in height for the separation of plutonium and thorium from americium. Ion exchange columns 10 cm. in height were prepared by conversion to the thiocyanate form for the separation of rare earths from americium. A 5N N H S C K solution was purified by passage through both Dowex 1 and Dowex 50 ion exchange columns. Solutions were freshly prepared for each use as decomposition was observed after a few days. Standards. Thorium oxide and plutonium metal were used to prepare standard solutions in 0.3N HC1 containing the equivalent of 10, 20, 50, 100, 200, 500, and 1000 p.p.m. of plutonium and thorium in a 20-mg. sample. The standard solutions contained 40 mg./ml. of americium and 0.1 pg./ml. of lutetium internal standard. One-hundred-microliter aliquots were added to electrode pairs. Rare earth standard solutions of 0.3N HCl were prepared from high purity rare earth oxides (99.9+'%) to cover the range from 10 p.p.m. to 1%. Recommended Procedure. Dissolve 22.6 + 0.1 mg. of AmOz sample by heating t o dryness with 5 ml. of equal volumes of 6 N HCl and a soluand 0 . 1 . ~in H F . tion 8 N in "03 Repeat twice. Dissolve the residue with 1 mi. of 8N "03. Transfer to an ion exchange column conditioned with 8N HNOs. Wash the americium and rare earths from the column with Change containers 20 ml. of 8N "01. and elute the plutonium and thorium with 20 ml. of 0.3N Add 50 pl. of a 1 pg./ml. lutetium internal standard to the plutonium and thorium solution and evaporate to dryness. Dissolve the residue with 500 pl. of 0.3N HCl and pipet 100-gl. aliquots onto electrode pairs and dry. Evaporate the portion containing rare earths and americium to dryness and redissolve with 1 ml. of 5N NHSCN. Transfer this portion to the ion exchange column conditioned with
5N NH4SCN. Wash the rare earths from the column with 5N NH4SCN until the americium concentration of the effluent reaches 2 pg./ml. a t approximately 65 ml. Elute the americium with 0.3N HC1. Heat the NH,SCN solution a t 200' C. to remove the water and then to 600" C. to destroy the NH4SCN. Add 3 ml. of 6N HC1 and 3 ml. of 8N HNOa-O.lN H F and evaporate to dryness. Dissolve the residue with 500 pl. of 0.3N HC1, pipet 200 pl. aliquots onto electrode pairs and dry. Excite and record the spectra under conditions given in Table I. Measure with the microphotometer the plutonium 3401.0-A, thorium 3325.12-A, and lutetium 3397.07-A lines. Determine the background corrections for each line. Determine intensity ratios and read concentrations from analytical working curves. Determine the rare earth concentrations by visual comparison with standard spectra.
Table 1.
Spectrographic Conditions
Excitation Capacitance Inductance Resistance Current Discharges Analytical gap Entrance slit Spectral region Pu and Th Rare earths PhotograDhic r&oiding Pu and Th Rare earths Exposure Pu and Th Rare earths Stallwood Jet Electrodes
High voltage a.c. spark 0.015 pf. 100 ph. Residual 12 R.F. amperes 1080/second 3 mm. 30 microns 3200-3800 A 1st order 3200-4400 A 1st order Eastman Kodak 103-0 Eastman Kodak SA-1 10 seconds 30 seconds 13 cu. ft./hour of 80% argon-2O%oxygen ASTM C-3
VOL. 38, NO. 8, JULY 1966
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Table II. Analysis of Americium Containing Known Concentrations of Plutonium and Thorium
Plutonium, p.p.m. Added Found
Thorium, p.p.m. Added Found
190 174 210 96 105 90 460 510 500 Rel. error -2.9%
50 50 50 100 100 100 200 200 200
200 200 200 100 100 100 500 500 500
56 56
Fin 96 220 190 250 ,6.8%
+
RESULTS
The precision for plutonium and thorium was determined by 15 replicate analyses on each of two samples. A standard deviation of 26 p.p.m, at 168 p,p.m. and 22 p.p.m. a t 147 p.p.m. was obtained for plutonium. Similar values obtained for thorium were 8 p.p.m. a t 79 p.p.m. and 3 p.p.m. a t 49 p.p.m. Precision data for the rare earths were not determined since their concentrations were obtained by visual comparison. Americium samples to which known amounts of plutonium and thorium were added were analyzed. The americium was purified by ion exchange prior to its use. Results are shown in Table 11. Detection limits for rare earths in p.p.m. were: Y(10), La(lO), Ce(100), Pr(100), Nd(100), Sm(50), Eu(25), Gd(25), Tb(25), Dy(50), Ho(25), Er(l0) Tm(25), Y b ( l O ) , and Lu(l0). DISCUSSION
The determination of plutonium in an oxide sample is dependent upon complete dissolution of Pu02. The effectiveness of various acid mixtures in dissolving 1% PUOZin Laz03as a substitute for AmOz was studied with 6N 6N HCl, and 8N HCl and 8 N "03, HNOr0.005N HF, and 6N HC1 and g N HNOA.1N HF as outlined in the Table 111.
recommended procedure. Radiochemical analysis showed only the 6N HC1 and 8N HNOaO.lN H F effected quantitative dissolution under these conditions. Elution studies showed that the column size and elution volumes used provided adequate separations. Some loss of plutonium in the VI state may occur during washing of the column with 8N "0s. This would explain the low recoveries of Table 11. Peak plutonium and thorium elution was at 8 ml. of 0.3N HNOs wash with less than 0.3% remaining after 20 ml. The peak elution of lutetium, the last rare earth to be eluted, was at 32 ml. of 5N NH,SCN. Less than 0.4% was eluted after 65-ml. volume. No effect from varying the amount of americium (0, 5, 10, 20 mg.) was observed on the ion exchange behavior of 100 pg. of plutonium. Spectrographic parameters were selected primarily to give maximum sensitivity. Copper spark gave less sensitivity for most elements than did graphite. The Stallwood Jet with an 80% argon-20% oxygen atmosphere gave increased sensitivity in addition to eliminating cyanogen interference. Use of a rotating platform electrode increased sensitivity only slightly. Moving plate studies showed the emission of plutonium, thorium, and rare earths to be a t a maximum at less than 10 seconds and nearly complete a t 30 seconds. Recording the plutonium and thorium spectra on Eastman Kodak 103-0 plate to obtain maximum sensitivity required reduction of the exposure to 10 seconds to avoid excessive background. Effects of other impurity elements on the analysis for rare earths were of interest as most impurities are not separated from the rare earths by the procedure outlined. Effects of 0.005, 0.05, 0.5, and 5% Ca, K, Fe, Pb, and Ce on the analysis of 50 p.p.m. of yttrium, as determined by a photometric procedure, are shown in Figure 1. The effect of other impurities on the determination of plutonium and thorium was not studied as complete separation is achieved from other elements of concern.
Americium in Thiocyanate Anion Exchange Column Effluent
VOl. fraction, ml.
Am concn., Fg./ml.
Am in fraction, rg.
Cumulative Am, rg.
0-50 50-55 55-60 60-65 65-70 70-75 75-80
0.006 0.043 0.240 1.068 3.427 7.217 21.877
0.30 0.22 1.20 5.34 17.14 36.08 109.38
0.30 0.52 1.72 7.06 24.20 60.28 169.66
'K
* 2 16'
1 IO-' I IO Impurity Concentration, Par cent Figure 1. Effect of other impurities on determination of 50 p.p.m. of yttrium
ANALYTICAL CHEMISTRY
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Spectral interference for the determination of low level rare earth impurities becomes excessive when the americium on the electrodes exceeds 10 pg. Considering the aliquoting made, 25 pg. may be allowed in the column effluent. The americium concentration of the effluent as determined by radiochemical analysis is shown in Table 111. Termination of collection of the rare earth fraction when the americium concentration of the effluent reaches 2 pg./ml. ensures freedom from excessive americium interference. The recommended method has been used for the analysis of approximately 30 americium oxide samples. While sample preparation is lengthy for an emission spectrographic method, the separations achieved permit the detection of low concentrations of actinide and lanthanide impurities. LITERQTURE CITED
(1) Barton, H. N., unpublished data,
The Dow Chemical Co., Rocky Flats Division, Golden, Colo., 1964. (2) Campbell, D. O., U. S. At. Energy
Comm. Rept. ORNL-1855, 1956. (3) Coleman, J. S., et al., J. Inorg. Nucl. Chem. 3, 327 (1956). (4) Faris, J. P., Buchanan, R. F., U.S. At. Energy Comm. Rept. TID-7606,p. 185, 1960. (5) Johnson, A. J., Vejvoda, E., Zbid., RFP-143, 1959. ( 6 ) Kressin, I. K., Waterbury, G. R., ANAL.CHEM.34, 1598 (1962). (7) Metz, C. F., Ibid., 29, 1748 (1957). (8) Scribner, B. F., Mullin, H. R., J . Res. Natl. Bur. Stds. A 37, 379 (1946). (9) Strain, J. E., Leddicotte, G. W., U.S. At. Energy Comm. Rept. ORNL-3355, 1963. H. N. BARTON
The Dow Chemical Co. Rocky Flats Division Golden, Colo. WORK supported under U. S. Atomic Energy Commission Contract AT(29-1)1106.
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