streaks. When the developing solution was Q.li11 hydrochloric acid, Ag(I), Cu(II), Sn(IV), and Bi(II1) remained at the origin, Th(IV), U(VI), Ti(IV), A1 (111), Zn(II), Y ( V , Pt(IV), Cd(II), Y(IXI), Sc(III), Er(III), Ni(II), and Fe(II1) traveled with the solvent front, and Sb(III),Pb(II), and Co(I1) formed streaks. When the pH of the developing solution was increased, more elements formed streaks on the chromatograms. Ultraviolet and visible spectra of IOTG and its complexes with bismuth (111) copper (11), gold(II1) mercury (11) and silver(1) were recorded (Figure 6). The spectra were measured in chloroform. All of these metal-IOTG complexes except niercury(I1) are yellOW.
The combining ratio of IOTG to mercury(I1) was found to be 2 : l by a titration in methanol-water using Thiomichler’s ketone as indicator. This would be the expected combining ratio
for a divalent metal ion if a neutral complex is assumed. The logarithnis of the distribution ratios for extraction of lead (11) and zinc(I1) into IOTGethyl acetate were plotted against pH. I n each case a straight line of slope approximately one was obtained, indicating that only one proton per metal ion is ejected during complex formation. Quantitative results were obtained for the extraction of bismuth(II1) with a dilute solution of isooctyl thioglycolate instead of first extracting with pure IOTG. However, longer shaking was required with the diluted reagent. Experiments were undertaken to find the relationship between the distribution coefficient and the concentration of the extracting reagent. The concentration of bismuth in 1M nitric acid was kept constant a t 5.0 x 1Q-?11bismuth nitrate and the reagent concentration was varied from 2.9 X 10-3JI to 4.8 X 10-2M in cyclohexane. Equal volumes of aqueous arid organic mere shaken for
quid Extra I uoroaceto
two hours. The organic phase was then back-extracted with 6M hydrochloric acid and analyzed spectrophotometrically (4). When the log of the distribution coefficient was plotted against the log of the IOTG molar concentration, a slope of 2.07 was obtained. This implies that the complex extracted consists of two moles of IOTG to one of bismuth. LITERATURE CITED
(1) Frits, J. S., unpublished work, 1965. (2) Fritz, J. S., .4bbink, J. E., Payne, M. A,, ANAL.CHEY.33, 1381 (1961).
(3) HandJey, T. H., Talanta 12, 893 (1965). (4)Merritt, C., Hershenson, H. M., Rogers, L. B., AXAL. CHEM.25, 572 (1953). (5) Underwood, A. L., Ibid., 26, 1322 (1954). RECEIVEDfor review July 22, 1966. Accepted October 11, 1966. Presented before the Division of Analytical Chemistry, Fq’inter Meeting, ACS, Phoenix, Ariz., 1966.
e Iiu m(IV)
ication to the Purification and mination of Berkelium FLETCHER L. MOORE Analytical Chemistry Division, O a k Ridge National Laboratory, Oak Ridge, Tenn.
A new, simple, rapid method for the radiochemical purification and determination of berkelium i s based on liquid-liquid extraction of berkelium (iV) with QSM 2-thenoyltrifluoroacetone-xylene. The high stability of the berkeliurn(lV) chelate provides marked selectivity from aqueous solutions of nitric, sulfuric, or hydrochloric acids. Sodium dichromate is an efficient oxidant for berkelium(lll) tracer under the conditions required for optimum chelation and extraction of berkelium(1V). Ten-normal nitric acid solution readily strips the berkelium from h e organic phase. Excellent sepcaration of berkelium is effected from many elements, including the alkalies, alkaline earths, trivalent lanthanides, ruthenium, zirconium, niobium, uranium, neptunium, plutonium, americium, curium, californium, iron, nickel, aluminum, and silver. Several useful analytical and process applications of this purification method are discussed.
associated with the radiochemical purification and determination of berkelium-249 were discussed recently (8). A two cycle IFFICULTIES
11
e
ANALYTlCAL CHEMISTRY
liquid-liquid extraction system was proposed a t the time. That method is of the ion association type, utilizing the di(2-ethylhexy1)orthophossolvents, phoric acid-heptane and tricaprylamine-xylene. Separation methods based on chelation with 2-thenoyltrifluoroacetone (TTA) possess much higher selectivity than those which function by the ion association mechanism. Indeed, TTA exhibits unparalleled selectivity for the chelation and extraction of zirconium(IV), neptunium(IV), plutoniuni(IV), cerium (IV), tin(IV), and iron(II1) (6, 7 , 1019).
The method described in this paper is based on the recent observation by the author that berkelium(1V) forms a highly stable chelate with TTA. It can be extracted essentially quantitatively from aqueous solutions containing nitric acid (0.5-3.5N), sulfuric acid (0.5l . O X ) i or hydrochloric acid (0.1N). Under these conditions very few metal ions form extractable chelates with TTA ( 6 , IO). The chelation and extraction of berkelium(1V) with TTA have not been reported previously. The extraction of berkeliurn(II1) with TTA at pH > 2 has been noted (3). Al-
though berkelium(II1) extracts readily under these conditions, the selectivity is very poor. Because of the considerable promise of a Bk(1V)-TTA system in separations chemistry, work was directed in this area. EXPERIMENTAL
Apparatus. An internal sample methane proportional counter with voltage settings of 2100, 2900, and 4300 was used for fission-fragment, alpha, and beta counting, respectively. A NaI (Tl) well-type scintillation counter, 13/4 x 2 inches, was used for gamma counting. Reagents. 2 - Thenoyltrifluoroacetone (TTA, M.W. = 222) is available from Columbia Organic Chemicals Co., Columbia, S. C. Procedure. Pipet a suitable fluoride-free aliquot, preferably containing 2 pg. or less of cerium, into a 50ml. borosilicate glass centrifuge tube. Adjust the aqueous solution to about 4.5-rnl. volunie containing about 1N nitric acid and 0.2X sodium dichromate. (As much as 100 pg. of cerium in the sample aliquot can be tolerated. I n this case, it is necessary to adjust the aqueous phase to about 4.5-ml. volume containing about 1N nitric acid-0.ZM
sodium dichromate-0.211'1 sodium bromate.) Mix the reagents gently and oxidize in a water bath at about 90" C. for 15 min. Add 0.5 ml. of 5N sulfuric acid solution to wash down the sides of the tube. After the solution reaches room telnperature, add 5 ml. of 0.5M TTAxylene solution. Mix thoroughly for 10 min. with a glass paddle stirrer driven by a high-speed motor. Centrifuge for 3 min. Carefully draw off and remove the aqueous phase with a transfer pipet or micropipet attached by rubber tubing to a vacuum trap. Scrub the organic phase by mixing well with 5 ml. of I N sulfuric acid0.2X sodium dichromate solution for 3 min. Centrifuge for 3 min. Draw off and discard the aqueous scrub solution. Again centrifuge for 3 min. For analytical purposes, it is convenient a t this point to mount 0.5 ml. of the organic phase on a stainless steel plate ( l l b / l G inch diameter). Heat to dryness on a hot plate at about 90" C. Ignite the plate to a red heat and allow it to cool to room temperature. Count the berkelium-249 alpha particles in an internal sample gas flow proportional counter. For purification purposes, strip the berkelium tracer from the organic phase by mixing well with 5 nil. of 10N nitric acid solution for 3 min. Discard the organic phase. I n purification work, one may wish to employ separatory funnels or more elegant equipment for increased maneuverability. RESULTS AND DISCUSSION
In principle the berkelium(1V) ion in aqueous acid solutions forms a stable chelate with 2-thenoyltrifluoracetone. In its simplest form, assuming no other complexing of the berkelium(1V) in the aqueous phase, the overall reaction presumably may be written as: Bk,+d +4HT, G BkT4,
+ 4Ha+
where H T is the enol form of TTA and BkT4 is the berkelium(1V) chelate. Subscripts a and o refer to the aqueous and organic phases, respectively. The mechanism of the reaction involves hydrogen replacement and coordinate bonding. Both the TTA and the berkelium chelate have negligible solubility in the aqueous acid solution but are highly soluble in xylene and many other solvents. The extraction of berkelium(1V) with 0.5M TTA-xylene from aqueous solutions of nitric, sulfuric, and hydrochloric acids is shown in Figure 1. Aqueous solutions of varying concentrations of each acid containing 0.221 sodium dichromate and 1.6 X lo4 beta c.p.m. were extracted for 10 minutes with equal volume portions of 0.5U TTA-xylene. High speed motor stirrers equipped with glass paddles were satisfactory. After centrifugation for 3 minutes, aliquots of the organic phases were analyzed for berkelium-249. The
= I Y
$ 5 m
1
2
4
3
5
ACID CONCENTRATION, N Figure 1. Extraction of berkelium(lV)-249 tracer from acid solution with 0.5M 2-thenoyltrifluoroacetonexylene
data (Figure 1) indicate that berkelium (IV) tracer extracts essentially quantitatively from aqueous nitric acid solutions in the range 0.5-3.5-V. Berkelium(1V) tracer extracts essentially quantitatively from aqueous sulfuric acid solutions (Figure 1) in the range 0.5-1.O.V. The decrease in extraction efficiency a t higher concentrations of sulfuric acid reflects the competition of increasing amounts of sulfate and bisulfate ions for berkelium(1V) in the aqueous phase. The efficient extraction of berkelium (IV) from aqueous solutions of hydrochloric acid (Figure 1) is most surprising. Berkelium(1V) and cerium(1V) are usually considered unstable in hydrochloric acid solution; thus, chloride ion is often used to catalyze the reduction of cerium(1V). Under the conditions described above, berkelium(1V) [and cerium(1V) to a lesser degree] exhibits high extractability from dilute hydrochloric acid solution with TT,4 in the presence of sodium dichromate. This is the subject of a continuing study. I n the nitric, sulfuric, or hydrochloric acid systems, reduction of the dichromate ion becomes marked in the range 4-5N. A variety of aqueous acidities (nitric acid, sulfuric acid, or mixtures of the two) can be used for the quantitative extraction of berkelium(1V). For a standard method, 1N nitric acid-0.5N sulfuric acid was selected, because >9Syo yield is effected, and the sulfate ion improves the general decontamination. The extraction of berkelium(1V) from 1 N nitric acid-0.5N sulfuric acid solution as a function of time is shown in Table I. Other conditions were the
same as those described for Figure 1. A 10-minute extraction period was selected for the standard method used in further evaluations. Because the oxidation potential of the berkelium(II1-IV) couple (- 1.62 volts in 1 N nitric acid) is essentially the same as that of the cerous-ceric couple (1) conditions for the oxidation of berkelium and cerium (11) tracers were observed to be very similar. Interestingly, the dichromate ion readily oxidizes tracer berkelium(II1) to berkelium(l[V), although the oxidation potential of the latter couple is more negative (by the Latimer convention) than that of the dichromate-chromic couple. Presumably, the oxidation occurs because the removal of the small number of berkelium atoms from the aqueous phase favors the reaction, berkelium (111) +berkelium(IV). Under the conditions required for optimum chelation and extraction of berkelium(1V) tracer, sodium dichromate was clearly superior to the other oxidants tested-e.g., ammonium peroxydisulfate, silver catalyzed ammonium peroxydisulfate, argentic oxide, potassium bromate, and potassium permanganate. An aqueous concentration of 0.2M sodium dichromate was used for most of the studies,
Table 1. Extraction of Berkelium(1V)249 Tracer from 1 N Nitric Acid Solution with 0.5M 2-ThenoyltrifluoroacetoneXylene as a Function of Time
Time extracted, min. 2
5 8 10
249 Bk tracer extracted,
71.9 81.3 98.8 99.6
VOL. 38, NO. 13, DECEMBER 1966
1873
Table II.
Effect of Cerium Concentration on Extraction of Berkelium-249 Tracer with O.5M 2-Thenoyltrifluoroacetone-Xylene"
Total cerium added, pg.
Cerium concn., NazCrZO7, M
pg./d.
0
0
2.2 2.8
0.2
... ...
0.44
0.2 0.2 0.2 0.2
3.3 5.5 10.1
0.55 0.66 1.10 2.02
25.3
5.05
0.2
10.10
0.2 0.2 0.2 0.2
0.2
0.2
50.5 101
20.20
0.2
...
488
0.2 0.2 0.2 0.2 0.2 0.2
97.6
1951 6
...
48.8
244
390.2
Each aqueous phase also contained
11%' HNOa-0.5iV
Table Ill. loss of Berkelum-249 from 0.5M 2-Thenoyltrifluoroacetone-Xylene Solution with Various Scrubbing Agents
Scrubbing agent Distilled Water lN HzS04 11%'
HXOs
249
Bk loss, % 2 . 8 X Io" 86Strontium >2 x 106 106Ruthenium 2.7 X lo2 1.43 x 103 Q6Zirconium-niobium 3.4 4.49 x 1 o 2 ( > 1 . 2 x 10415 1"-4Europium > 2 . 5 X lo6 2SWranium 2 . 6 x 104 2 Weptunium 1.84 X IO8 239Plutonium 1 . 7 X IO8 241Americium > 2 . 4 X lo6 244Curiurn > 8 . 6 X 106 262Californium > 6 . 8 X lo4 691r0n 8.8 1 . 3 5 X IO2 (1.38 X IO3)" T3ilver 8 X IO8 Nickel > 1 . 3 X loa Aluminum 1.1 x 104 After a 5-min. re-extraction of the strip solution with a equal volume portion of 0.5M TTA-xylene. 5
predicted to behave quite similarly to californium. If desired, the decontamination of berkelium from zirconium and iron can be increased further by re-extracting the 10N nitric acid strip solution with TTA. Thus, a 5-minute extraction with an equal volume portion of 0 . 5 N TTA-xylene solution reduced the zirconium and iron content to negligible values (Table VI) ; the berkelium remained quantitatively in the aqueous phase. The procedure was designed to separate berkelium(1V) from neptunium (VI) and plutonium(V1). To accomplish this, it was necessary to oxidize a t about 90" C. for 15 min. in the absence of the sulfuric acid to ensure that the neptunium and plutonium were in the inextractable sexavalent oxidation states. Because sulfuric acid strongly inhibits the oxidation, it is added afterwards, just prior to the extraction. In the absence of neptunium and plutonium, a 5-minute oxidation period at room temperature in the presence of the sulfuric acid is quite adequate for berkelium.
As suggested previously (8), preliminary coprecipitations of berkelium wit'h lanthanum hydroxide and lanthanum fluoride is an excellent method for isolating and concentrating berkelium from solutions of questionable history, The TTA method for berkelium is quite flexible, depending on the objective-whether for purification or radiochemical determination of berkelium. For analytical purposes, the procedure can often be shortened. Thus, after scrubbing and centrifuging the organic phase, one simply evaporates an aliquot for alpha particle measurements. Alpha counting (8) and alpha spectrometry are recommended for berkelium-249. In principle, beta counting can be used on rigorously purified samples; however, the accurate determination of small amounts of berkelium-249 in highly radioactive solutions containing transuranium elements and fission products by beta counting borders on the impossible. This does not preclude the future possibility of using beta counting in certain situations involving relatively lorn levels VOL 38, NO. 13, DECEMBER 1966 a
189
of radioactivity-e.g., in biological and health physics problems. Fluoride ion must be removed OF effectively compIexed prior to the extraction. Chloride ion concentration should not exceed 0.5-V. Recoveries through the standard procedure averaged 98.8% berkelium-249 with a relative sta.ndard deviation of 0.5% (n = 6). ANALYTICAL APPLICATIONS
The TTA method simplifies the determination of berkelium nuclides produced in transuranium element processes and the preliminary isolation of berkelium prior t o study by other methods. A most practical advantage is the ease of plate preparation for alpha measurements. One simply evaporates an aliquot of the TTA-xylene solution on inexpensive stainless steel plates. After ignition, the essentially solid free plates produced are excellent for alpha spectrometry. On the author’s particular counting arrangement (silicon diode detector = 3 sq. cm.), a resolution of about 40 k.e.v. is possible. Because such resolution closely approaches that possible with electrodeposited plates, the need for an additional electrodeposition step is obviated for most work. In the method (8) currently used for berkelium, the direct evaporation of the high boiling solvents, di(2-ethylhexy1)orthophosphoric acid or tri-
caprylamine, is precluded because of the solids problem. Moreover, the use of hydroch’oric acid necessitates expensive platinum or tantalum plates.
in the experimental work and of TV. R. Laing for some of t’he analyses. He is also indebted to R. D. Baybarz for sharing his berkelium tracer.
GENERAL PURIFICATION W O R K
LITERATURE CITED
The TTA method is promising for the general purification and isolation of berkelium nuclides in preparative and industrial work. It is readily adaptable to remote control and continuous countercurrent processing a t room temperature; TTA can be easily recovered for re-use. It provides higher separation factors from other actinide elements, fission products, and associated elements than any other single solvent developed t o date. Although no studies have been done on its radiation resistance to alpha particles, TTA possesses relatively high stability to gamma radiation. Zittel ( I S ) observed no detectable effect a t an accumulated dose of 1 X loEr. For the difficult separation of berkelium(ITi) and cerium(IV), a promising avenue lies in the application of the, TTA method in multistage systemse.g., liquid-liquid extraction or extraction chromatography. Although these elements can be separated in other systems ( I , 4, 6 ) , none of these methods provides the concomitant high selectivity possible with TTA.
(1) Higgins, G. H.,. “The Radioc%mistry of the Transcurium Elements, NASNS-3031 (1960). (2) Katz, J. J., Seaborg, G. T., “Th: Chemistry of the Actinide Elements, p. 437, Wiley, New York, 1957. (3) ?vIagiiusson, L. E., Anderson, M. L., J . Am. Chem. Sac. 76, 6207 (1954). (4) itfoore, F. L., ANAL. CHEW33, 748 (1961). (5) Ibid., 36, 2188 (1964). (6) Moore, F. L., “Metals Analysis with
ACKNOWLEDGMENT
The author gratefully acknowledges the capable assistance of G. I. Gault
TTA,” Symposium on Solvent Extraction in the Analysis of Metals, ASTM Spec. Tech. Publ. No. 238 (1958). (7) Moore, F. L., Fairman, W. D., Ganchoff, J. G., Surak, J. G., ANAL.CHEM.
31, 1148 (1959). (8) Noore, F. L., Mullins, W. T., B i d , , 37, 687 (1965). (9) Peppard, D. F., nloline, 8. W., Mason, G. W., J . Inarg. Nucl. Chem. 4, 344 (1957). (10) Poskanzer, A. hl., Foreman, B. M., Jr., Ibfd., 16, 323 (1961). (11) Smith, G. W., Moore, F. L., ANAL. CHEV.29, 448 (1957). (12) Stokely, J. R., Moore, F. L., Ibid., 36,1203 (1964). (13) Zittel, H. E., Oak Ridge National Laboratory, Oak Ridge, Tenn., personal communication (1964).
RECEIVEDfor review August 3, 1966. Accepted October 14, 1966. Research s onsored by the U. S. Atomic Energy 8ommission under contract with the Union Carbide Corp.
Base-Catalyzed Hydrogen-Deu terium Exchange in Bivalent Metal-EDTA Chelates J. 6. TERRlLL and C. N. RElLLEY Department of Chemistry, University of North Carolina, Chapel Hill, The hydrogen-deuterium exchange in alkaline heavy-water solutions at 95’ C. of bivalent metal-(ethylenedinitrile)-tetraacetates (denoted EDTA) was followed with nuclear magnetic resonance (NMR) spectrometry by observing decreases in spectral intensities. The exchange process, studied in 0 . l M to 0.8M OD-, was first order in complex and first order in OD-. The order of reactivity of the metal chelates, C U + ~ Nif2 Co+2 Zn+2 Pb+2 Cd+2 Mg+2 Ca+Z Sr+2 Ba+2,correlates well with the strength of the metal-ligand bonds. Only the acetate methylene protons exchanged at a measurable rate. In similar studies with unassociated model compounds, a much slower OD- hydrogen-deuterium exchange was observed for acetate and
>
>
1876 *
>
>
>
>
>
>
ANALYTICAL CHEMISTRY
>
N. C. 275 14
glycinate; in contrast, the exchange rates for imidodiacetate (IDA), ethylenediamine N,N’ diacetate (EDDA), and EDTA were faster and were zero order in OD-, suggesting an intramolecular base-catalysis process.
-
F
-
of bonds between a metal ion and a ligand molecule results in significant ohanges in the chemical properties of the organic compared to those of the unassociated ligand molecule. Extensive investigations of the chemical properties of the met,allocene (ferrocene) and the metal acetylacetonate complexes have often illustrated the differential chemical behavior of the chelate to that of the free ligand (1, 7, 18, 83). As most of these studies were done in nonaqueous media, a large variety of reactions were feasible, ORMATION
In aqueous media, notable studies have been made of the enhancement of the rate of hydrolysis in the metal peptide (9)and amino acid ester (8) complexes over that of the free ligand. The enhancement in reactivity of the glycinate methylene protons in glycinato-bis(ethglenediamine)cobalt(III) denoted [ C ~ ( e n ) ~ g l y +over ~ ] that of the unreactive unassociated glycine was shown by the successful condensation of the cobalt complex with acetaldehyde to give theonine (8% optical yield) (bI,92). Subsequently, Williams and Busch observed the hydrogen-deuterium exchange of the acetate methylene proton in basic heavy-water solutions of three cobalt(II1) chelates: [ C ~ ( e n ) ~ g l y ] + ~ , [Co(en)2(al)]+z, and [CO(EDTA)]+~, where a1 is alanine (SO). The influence of molecular stereochemistry on hydro-
