ent as impurity in the other stereoisomer.
V. Water-saturated collidine (2,4,6trimethylpyridine) (6).
G., “Paper Chromatography and Pa er ElectroDhoresis,” Academic Press, &w York, 1958. (3) Dum, M. 8. Murphy, E. A., ANAL. CHEM. 32,401 (1900). (4) Hamilton, P. B., Andereon, R. A,, J . B i d . C h q . 213,249 (1955). (5) McFarren, E. F., ANAL.CIiEM. 23, I
EXPERIMENTAL
Color Reagents. Isatin (9,p. 136) for proline impurity, isatin and pdimeth laminobenzaldehyde (S, p. 126) for hy&oxyproline impurit , 1-nitroso%naphthol (8, p. 139) &r tyrosine impurity in alanine and proline, and ninhydrin (7) for all other tests. Solvents. I. tert-Butyl alcoholformic acid-water, 70: 15: 15 (1). 11. Phenol-water, 78: 22 and then this mixture-concentrated ammonia, 94: 1 (7). 111. Phenol-buffer (pH 6.2), 78:22 (6). IV. Phenol-buffer (pH 9.0) 78:22.
Test Conditione. The details of the procedures employed in the chromatographic purity testa of the six amino acids summarized in Table I are given on the preceding page. ACKNOWLEDGMENT
The authors are indebted to Moichi Itami for technical assistance. LITERATURE CITED
(1) Block, R. J., ANAL.CHEM.22, 1327 (1950). (2) Block, R. J., Durrum, E. L., Zweig,
(0)108 Michi, (lg51k ., Birnbaum 8. M., Winits,
“Abstracts of bapers,” 130th z i e t i n ACS, Atlmtic City, N. J., Se temker 1959, p. 19C. (7) &ockland, L. B., Underwood, J. C., ANAL.CHEM. 26,1557 (1954). RECEIVED for review January 18 1961. Accepted April 27, 1961. Work supported by grants from the American Cancer Society, U. 5. Public. Health Service, and University of California.
Spectro p hoto metric Extracti0 n Method Specific for PI uto nium WILLIAM J. MAECK, MAXINE ELLIOTT KUSSY, GLENN L. BOOMAN, and JAMES E. REIN Atomic Energy Division, Phillips Petroleum Co., Idaho Falls, Idaho
b A spectrophotometric extraction method for milligram levels of plutonium is described. Following a silver (11) oxidation, plutonium(V1) as the tetrapropylammonium trinitrate complex is extracted quantitatively into methyl isobutyl ketone from an aciddeficient aluminum nitrate salting solution. Though uranium and neptunium are extracted also, their spectra are sufficiently discrete so that a direct absorbance measurement of the separated organic phase can b e made for plutonium in the presence of the other two actinides. The method is fast, gives excellent decontamination from fission product nuclides, and is virtually free of diverse ion interference. It is applicable to the range of 2.0 to 15 mg. of plutonium with a 0.3% standard deviation at the 12.3mg. level, comparing favorably with redox titrimetric and coulometric methods. A method for the simultaneous determination of plutonium and uranium is described.
P
in aqueous media, exhibits sharp band spectra typically charactoristic of inner transition elements. Each oxidation state, 111, IV, V, and VI, has a discrete spectra with maximum molar absorptivities of 50 to 280. The main application of these data in the past has been the establishment of oxidation-reduction rates and kinetics of reaction rather than serving as bases for analytical methods. In a review article on the analytical chemistry of plutonium, Mets (7) states that the molar absorptivities are deLUTONIUM,
998
0
ANALYTICAL CHEMISTRY
pendent on temperature, pB, anion species, and anion concentrhtion. This behavior is due to the effect of these variables on the formation constants of the various anionic complexes. In addition, any method based on direct m e a urement in aqueous media would be sensitive to diverse , ion interference, especially for the elements in the transition and inner transition groups. Formation of the tetrapropylammonium uranium(V1) trinitrate complex and its extraction into methyl isobutyl ketone from an acid-deficient salting media followed by a direct absorptiometric measurement of the organic phase has been shown to be a rapid, reliable method for the determination of milligram quantities of uranium (6). The of tetrabutylammonium spectrum plutonyl trinitrate in methyl isobutyl ketone, reported by Berkman and Kaplan (S),indicated that a similar system would be applicable for plutonium and that the spectra of the two trinitrate complexes would be sufficiently different to permit a simultaneous determination of the two elements. The spectrum of the neptunium homolog is presented. EXPERIMENTAL
Apparatus and Reagents. All spectrophotometric measurements were made with a Gary Model 14 recording spectrophotometer and 1-cm. Corex cells. The extraction apparatus has been described (4). The source of chemicals and the preparation of the salting solution have been described (6). Silver(I1) oxide was obtained from
Handy and Harman, 82 Fulton St., New York 38, N. Y. Procedure. Samples of 0.5 ml. or leas containing u p to 6 meq. of acid and as much as 15 mg. of plutonium can be extracted from a salting solution which is 0.025M in tetrapropylammonium nitrate and 2N acid-deficient. With the 0.025M tetrapropylammonium nitrate reagent, the sum of plutonium, uranium, and neptunium in the sample aliquot is limited to 15 mg. Larger sums require higher concentrations of tetrapropylammonium nitrate. The preparation of a 0.25M tetrapropylammonium nitrate reagent - has been described (6). PiDet a chloride-free samde of 0.5 ml. i r less, containing from-0.5 to 15 mg. of plutonium, into a 125 X 15 mm. test tube. Add 0.05 ml. of 15.7M nitric acid and heat to boiling. Cool; then add 50 mg. of silver(I1) oxide and 5 ml. of 2.8M aluminum nitrate, 2N aciddeficient, 0.025M tetrapropylammonium nitrate salting solution. Add 4.0 ml. of methyl isobutyl ketone, stopper with a polyethylene stopper, and extract for 4 minutes. If possible, centrifuge to facilitate phase separation; otherwise let stand until the organic phase is clear. Transfer the organic phase to a 1-cm. Corex cell and scan over the wave length region of interest os. methyl isobutyl ketone. (A significant reagent blank has not been observed.) If chloride is present, place the sample in a test tube and either fume twice with 0.5-ml. volumes of 15.7M nitric acid and dilute to 0.5 ml. with 2M nitric acid before the silver(I1) oxide addition, or reduce the volume to 0.1 ml., add 0.4 ml. of 0.1M potassium permanganate, and heat 3 minutes b y holding the test tube 4 inches away from
an infrared lnmp before the salting solution addition.
Table 1.
(12.3 mg. of plutonium taken for extraction in all experiments)
DISCUSSION AND RESULTS
Oxidation and Extraction. Plutonium(1V) forms a light green precipitate with tetrapropylammonium nitrate which distributes to the methyl isobutyl ketone phase as a sparingly soluble complex. The plutonium(V1) complex is soluble. Manganese(VII), potassium permanganate, has been used as the oxidant to obtain the seldvalent state of plutonium for the radiochemical determination of that element (6). Recently, silver(I1) oxide has been used for the oxidation (8). Both potassium permanganate and silver(I1) oxide were evaluated for the oxidation and extraction of milligram quantities of plutonium (Table I). The conditions for these experiments were essentially as given in the procedure. In the permanganate experiments, the extraction mixing time was fixed at 4 minutes and the reaction time indicated is the time of standing after addition of the potassium permanganate and before addition of the aluminum nitrate salting solution. The reaction time for the silver(I1) oxide experiments is the extraction mixing time; no prestanding time was used. The absorbance value of 0.752 (obtained for the silver oxide oxidation) corresponded to an extraction of greater than 99.5y0 of the plutonium established by alpha counting of aqueous phases after extraction. Both hot potassium permanganate with a 3-minute standing time and silver(I1) oxide a t room temperature with a 2- to 4-minute mixing time are satisfactory. The slightly low (but not statistically significant) recovery of the potassium permanganate experiments compared to the silver(I1) oxide data may be due to adsorption and carrying of plutonium on the Mn02 precipitate that forms. Silver(I1) oxide was selected for its advantages of room temperature oxidation, speed, and complete dissolution during the mixing. Chloride forms a precipitate on the surface of the silver(I1) oxide which prevents further oxidation of plutonium. To analyze samples containing chloride, a double nitric acid fuming followed by the silver oxide oxidation or use of potassium permanganate without pretreatment were satisfactory. Spectra. The spectra, for the wave length region of 400 to 1200 mp, of the three actinides individually carried through the procedure are presented in Figure 1. The added amounts of each actinide were 12.3 mg. of uranium, 11.4 mg. of neptunium, and 12.3 mg. of plutonium. The extraction of uranium is 99.8% (4), and since that of plutonium is greater than 99.5%, neptuninum extraction is considered
Effect of Oxidizing Conditions on Extraction of Plutonium
Reaction Time, Min.E
Oxidant
Absorbance at Pu No. of 502-M ETtracted,@ MultiPu Peab % plicates
Cod. of Vari-
ation
0.04 mmole KMnO4, no heat
1
0 725
90.0
4
2.0
0.04 mmole KMnO4, plus heating
0.5
0.692
92.0 98.3
1 1
...
0.743
3.0 4.0
0.748 0.748 0.748
99.0 99.0 99.0
4
0.45
1
0.5 2.0 4.0
0.676 0.750 0.752 0.752
90.0 >99.2 >99.5 >99.6
1 1 5 1
... ... ...
2 _. 0_
6.0
60 mg. AgO, no heat
6.0
I
1
...
...
0.40
...
Time of standing before adding salting solution in case of KMnO,; time of mixing the two h a w in cam of AgO. * fitwe line corrected. 0 Based on 0.752 absorbance as greater than 99.5% extraction.
LO1
WAVE LENGTH. mp
'"I8
WAVE LENGTH,
evaporation of methyl isobutyl ketone, no change in absorbance was detected for 1.5 hours. After a total elapeed time of 4 hours, the absorbance at the 502mp peak had decreaeed 1% for an original 12.3-mg. plutonium sample. Calculation of Plutonium Concentration. With a scanning spectrophotometer, highest reliability is obtained by careful adjustment of the b w line to zero absorbance over the wave length region of interest, with a blank carried through the procedure prior to scanning samples. Because this technique is time-consuming, it is seldom used for routine analytical work. Compensation for a vertical base line shift can be made by using the absorbance difTerence at two wave lengths usually one at the absorbance peak and the other at the lowest valley adjacent to the peak. Additional compensation for a change in
my
Figure 1. Spectra of tetrapropylammonium trinitrate complexes of uranium(VI), neptunium(VI), and plutonium(V1) in methyl isobutyl ketone
to be virtually complete. The molar absorptivities at the most sensitive absorption peaks are 31.4.for uranium at 452 mp, 50.9 for neptunium at 447 mp, and 65.3 for plutonium at 502 mp. Details of the plutonium spectrum at this major peak are presented in Figure 2. Because of the sharp band spectra, a scanning spectrophotometer facilitates the analytical application. Stability of Plutonium Complex. I n a 1-cm. cell sealed to prevent
Table II. Comparison of Techniques foi Calculating Plutonium Concentration
(Eight determinations for each method) Coeff. Average of Value Variation Total absorbance at 50Zmp peak 0.843 Absorbance difference, 502 to 0.763 619 mp Three-wave length method, 502-mp peak, 519-mp and 456mpvalleys 0.755
VOL. 33, NO. 8, JULY 1961
0.35 0.27
0 23
999
h
I 00
u 4eo
400
L I qao
WWE
I
I
475
500
L w a r u , my
Figure 3. Absorbance curve for 1.5 mg./ml. each of uranium and plutonium as tetrapropylammonium trinitrate complexes in methyl isobutyl ketone Wove lengths selected for matrix calculation are marked
00 400
452mp uranium peaks and the 502-mp plutonium peak and the 519-mp valley. Based on a series of eight pure plutonium runs with 12.3 mg. of plutonium, the most precise ratio was:
A
1
I
e a
450 WWE
6
500
4'5
Lworn, mp
Figure 2. Details of tetrapropylammonium plutonyl trinitrate complex spectra in methyl isobutyl ketone at sensitive 502-mp peak wave length region
base line slope involves the use of absorbance measurementa a t three wave lengths, the peak and the valleys on both sides. The absorbance used is the peak absorbance value minua the absorbance value at the peak wave length of a line drawn tangent to the two valleys. This technique is shown in Figure 2. Relative data concerning these three approaches for a series of eight samples of 12.3 mg. of plutonium are presented in Table 11. The fact that the precision for the single-wave length method was only slightly poorer (and statistically insignificant at the 95% confidence level) indicates that the base line errors were negligible. The precision of the matrix method described below was 0.30%.
Table 111.
Added, Mg. Pu U 0 0 2.05 4.10 10.25 8.20 6.15 4.10 2.05
2.05 12.3 2.05 2.05 2.05 4.10 6.15 8.20 10.25
Analysis
of
Uranium-Plutonium
Mixtures. RATIO METBOD. The absorbance of uranium a t 456 mp prevents use of the three-wave length method for plutonium a t the most sensitive peak of 502 mp. Various correlations were studied for the simultaneous determination of uranium and plutonium in binary mixtures. Based on the assumption that the spectrum for plutonium in Figure 1 represents essentially only one species, absorbance a t all wave lengths should be proportional to plutonium concentration over ranges conforming to Beer's law. Various ratios of absorbance due to plutonium a t a uranium peak wave length divided by an absorbance value for plutonium a t 502 mp were computed. The wave lengths used were the 436- and
Analysis of Uranium-Plutonium Mixtures
A"*P"
+u
0.065 0.409 0.086 0.105 0.175 0.220 0,265 0.312 0.301
For a single determination,
ANALYTICAL CHEMISTRY
Molar Absorptivity U Pu
AW'P"
A"'p,
0 0 0.139 0.278 0.710 0.562 0.420 0.282 0.145
0 0 0 013 0.025 0.070 0.054 0.041 0.030 0.018
30.2 31.7 30.2 29.7 32.5 31.8 31.4 30.9 31.3
64.8 64.8 66.2 65.5 65.3 65.7 67.6
Av. Std.dev.'
31.1 0.90
65.7 .97
... ...
The average value of K was 0.1636, with a standard deviation (single determination) of 0.0013. The relationship, using this K to compute the uranium absorbance a t 452 mp, is: A45ZL,
= A4EP u
+ PU
- K(A502pu - A 6 1 q ~ u )
Mixtures of uranium and plutonium were processed through the rerommended procedure, and uranium concentration was computed from the above equation with K = 0.1636. Results (given in Table 111) are expressed in molar absorptivity for both uranium and plutonium, using the two-wave length procedure for plutonium. The average molar absorptivity value of 31.1 for uranium agrees to aithin 1% of the value of 31.4 reported previously (6). The average value of 65.7 1.0 for plutonium is not significantly different than the value of 65.4 + 0.3 obtained for the eight pure plutonium analyses from which the constant K was computed. An estimate of the precision for the deterrrination of both uranium and plutonium by this procedure is also shown in Table 111. For a single determination, the standard deviation for uranium is 2.901, and for plutonium is 1.5%. Examination of the data shows no significant effects of one actinide upon the other indicating that the K value is substantially correct and that uranium does not significantly contribute to absorbance a t the selected wave lengths for plutonium. Because this experiment was primarily designed to show the utility of the tetrapropylammonium-actinide trinitrate method, further data should be obtained before applying the stated
*
absorptivities and equations to routine analytical samples. MATRIX METHOD. In cases where several species contribute to the absorb ance at an analytically important wave length or if effects of base line shift and slope require correction, only the threewave length method discussed is adequate. The advantages and techniques of matrix methods have been described (1, 9). The evaluation of the constants for the equations relating absorbance a t the selected wave lengths to the concentration of each of the actinides is required. With these constants determined, the equations for the absorbance a t each of the selected wave lengths are written in the form : A I = K&l+ KdA
+ . . . + KnC. + a + b h
Solving this set of rn equations (m > n) gives an expression for the concentration of each species as well as for the base line shift, a, and the base line slope,
b.
to 1.2% and for plutonium from 1.5 to 1.0%, expressed in concentration units. As stated in the ratio method, further data should be obtained before applying the stated absorptivities and the resulting concentration equations to routine analytical samples. Analysis of Other Actinide Mixtures. Examination of the spectra presented in Figure 1 indicntes the following possibilities for analyzing other binary actinide mixtures and the ternary mixture. NEPTUNIUM-PLUTONIUM. Plutonium can be determined almost free of neptunium effects a t the 806-mp peak, especially if a two-wave length technique is used. (Sensitivity is about half that of the 502-mp peak.) For neptunium, the same technique as used for uraniumplutonium mixtures appears applicable with the 448-mfi neptunium peak. URANIUM-NEPTUNIUM. The determination of neptunium appears straighb forward by using a peak where uranium contributes no absorbance. The 564-mp peak is a logical choice. The determination of uranium is more difficult because of overlapping spectra. The 467-mp uranium peak seems best separated. Correction for neptunium absorbance would be required.
cant absorbance above 480 mp; thus, the plutonium determination is not affected. Chromium, which is oxidized to dichromate, extracts to a high aegree. The absorbance continuously increases with decreasing wave length. The determination of plutonium may be made using the 806-mp peak by a twoor threewave length procedure. The change in absorbance with wave length in this region is not significant even with 0.15 mmole of added chromium. T o analyze uranium-plutonium mixtures containing these elements, the matrix method is recommended. Fission Product Distribution. Data showing the distribution of fission product activity in this extraction Bystem with potassium permanganate as oxidant have been presented for 1month and 1.5-year cooled samples (6). Use of silver(I1) oxide does not change these distributions significantly. A decontamination factor of at least 100 was obtained for all nuclides. LITERATURE CITED
(1) Barnett, H. A., Bsrtoli, A., ANAL. Using the uranium and plutonium CHEM.32, 1153 (1960). data from this study, four absorbance (2) Baumann, R. P., Appl. Spectroscopy equations may be written in the follow13. 156 (1959). -, (3)Berkmxn M. G., Kaplan, Louie, ing matrix notation: U. S. At. hnergy Comm., Rept. ANL4573 (1951). (4) Maeck, W.J. Booman, G. I,., Elliott, Mg.u 0.00089f 0.0002 0.00649f 0.00015 1 10 M. C., Rein, E., ANAL. CHEM.30, Asia 0.0007 1 0.00044f0.0002 0.0085 A w1 1902 (1958). (6)Zbid., 31,1130 (1959). 0.00390f O.ooOo8 0.00927f 0.00016 1 1 (6) Maeck, W.J., Booman, G. L., Kussy, A ab 0.01005 f 0.00015 1 0 0.0333 f 0.0003 Atu M. E.. Rein. J. E..Ibid.,. 32.. 1874 (1960).' (7) Meta, C. F.,Zbid., 29, 1748 (1957). (8)Seils, C. A., Larsen, R. P., Meyer, URANIUMNEPTUNIUM - PLUTONIUM. R. J., 4th Conf. on Anal tical ChemThe precision of each of the absorpistry in Remtor TechnoLgy, GatlinOnly plutonium can be accurately detertivities is an estimate of one standard burg, Tenn., 1960. mined by using the 806-mfi peak. deviation. The four wave lengths were
5.
*
-
approximated by the series 0, 1, 7, and 10 to simplify the calculations. Expressions for the amount of uranium and plutonium in the sample as a function of the absorbance at the four selected wave lengths were: Mg. Uranium = +4.012 Aslo 0.2662 Am - 38.25Atso 34.50 Atsr
+
+
Mg. Plutonium = -10.84 Art$ 16.36Am - 6.15 Adso 0.6334Acsr
+
Figure 3 shows the position of these four wave lengths on a spectral recording of a uranium-plutonium mixture. These equations completely remove any absorbance contribution equivalent t o a base line shift or slope. Calculation in this manner is a perfectly general approach to improving any data of similar form and will have maximum usefulness where sharp absorption bands or their analogs are available. Using these derived equations, data from the mixtures in Table I11 were recalculated, with a resulting reduction in the coefficient of variation for uranium from 2.9
Multi-wave length measurements would be necessary to determine uranium and neptunium. Effects of Diverse Ions. The effects of 25 cations and 21 anions upon the extraction and determination of milligram levels of uranium with the same system, except for the oxidation step, have been studied (6). Only thorium and cerium interfered by combining with the tetraalkylamine to form a nonabsorbing thorium complex and a slightly absorbing cerium complex. This interference waa overcome b j using higher concentrations of the amine. No common anions interfered. The effect of the oxidation step becomes significant if some ion is oxidized to an oxidation state which extracts and spectrally interferes or if a precipitate forms that carries plutonium. Of the cations and anions previously investigated for uranium, chromium, cerium, and chloride were considered to merit further study. The effect of chloride has already been discussed in a previous section of this paper. With the silver(I1) oxide procedure, 0.25 mmole of cerium showed no signifi-
RECEIVEDfor review January 19, 1961. Accepted March 22,1961.
Correction Spectrochemical Determination of Boron in Saline Waters In this article by R. C. Reynolds, Jr., and John Wilson [ANAL. CHEM.33, 247 (1961)], the following corrections should be noted : Page 248, Table 11: The heading of the first column, which reads 2898 and 2894, should read 2498 and 2494; the symbol u should read S; 0.021/0.759 X 100 should be changed to (0.0211 0.759) X 100. Page 249, column 2, lines 9 and 11, salinity units should be given as 700, and not %OO. In column 3, the received date should be August 4, 1960 and the accepted date should be October 25, 1960. VOL. 33,
NO. 8, JULY 1961
1001
