1814
Anal. Chem. 1986, 58,1814-1816
-try NO.DMCA, 2316-26-9;MCA, 830-09-1;CA, 621-82-9; FA, 1135-24-6; HCA, 7400-08-0; y-oryzanol, 11042-64-1.
LITERATURE CITED
1 2 4 6 Duration after administration (hr)
Figure 7. Change of FA concentratlon In plasma after oral administration of yuyzanol in dogs. Each point represents the mean of three
measurements. ACKNOWLEDGMENT We thank Shigeru Terabe, Faculty of Engineering, Kyoto University, and Taka0 Tsuda, Nagoya Institute of Technology, for their helpful advice.
(1) Mkkers. F. E. P.; Everaerts, F. M.; Verheggen, Th. P. E. M. J . Chrom t o g r . 1979, 169, 1-10, ( 2 ) Jorgenson, J. W.; Lukacs, K. D. AM/. Chem. 1981, 5 3 , 1298-1302. (3)Terabe. S.; Otsuka, K.; Ichikawa, K.; Tsuchiya, A,; Ando, T. Anal. Cham. 1984, 56, 111-113. (4) Terabe, S.;Otsuka, K.; Ando, T. Anal. Chem. 1985, 57, 834-841. (5) Jorgenson, J. W.; Lukacs, K. D. J. Chrometogr. 1981, 218, 209-216. (6) Jorgenson, J. W.; Lukacs. K. 0 . Clln. Chem. (Wlnston-Salem, N . C . ) 1981, 2 7 , 1551-1553. (7) Tsuda, T.; Nomura, K.; Nakagawa, G. J . Chromatogr. 1983, 264, 385-392. (8) Tu&, T.; Nomura, K.; Nakagawa, 0.J . Chromtogr. 1982, 248, 241-247. (9) Tsuda, T.; Nakagawa, G.; %to, M.; Yagi, K. J . Appl. Biochem. 1983, 5,330-336.
(IO) IUPAC Ionization Constants of Organic AcMs in Aqueous Solutions;
Pergamon: Oxford, 1979. (11) Fujlwara. S.; Noumi, K.; Sugimoto, 1.; Awata, N. Chem. Pharm. Bull. 1982, 3 0 , 973-979. (12) Fujhvara, S.; Hamda, T.; Sugimoto, 1.; Awata, N. Chem. pherm. Bull. 1983, 3 1 , 1079-1081.
RECEIVED for review January 7, 1986. Accepted March 17, 1986.
Extraction of Trivalent Lanthanides by a Mixture of Didodscylnaphthalenesulfonic Acid and a Crown Ether Dale D. Ensor,* Gary R. McDonald, a n d C. Greg Pippin Chemistry Department, Tennessee Technological University, Cookeville, Tennessee 38505
DkWecybtapMdmwModc add, HDDNS, has been shown to be a useful IIqukHicpdd c a m e x c h a m for IanthanMe
elements. I t s * ~ a c l d c h a r a c l . r m e k e s t h e ~ a n dfectlve extradrtnt even at b w pH, bul il shows #me abillty to separate imllvwwl trlvaknt lanthanide ions from each other. I n an effort to introduce more wkctMty Into W extraction of lanthsnkle lone by HDDNS, a study of the effect of the addftlon of a crown ether, 4-~rbbutykycbhexyI-15wa8 made. The recrown45 (15-C-5), to the organk phsults of ihe extraction of Ce(III), Pm(III), Eu(III), and Tm( I I I) by HDDNS/tokrene and HDDNS/lS-CJ/toluene mlxtures are reported. The addttkn of the 154-5 produced measursynergistic eftot the extraction of the llght lanthanides, while the Tm( III)was rdatlvely unaffected.
The aqueous chemistry of the lanthanide elements is somewhat limited compared to other metals due to the predominance of the 3+ oxidation state. This charge similarity rules out charge-selective differentiation of lanthanides in water. In general, the elements of the lanthanide family have similar chemical properties and ionic size that make them difficult to separate from each other (1). Since enhanced separation of the lanthanides from each other and the chemically similar trivalent actinide elements is essential to reaearch 0003-2700/86/0358-1814$01.50/0
and practical applications of these metals, the goal of this work was to improve the selective separation of lanthanides. The use of dialkylnaphthalenesulfonic acids as a liquid cation exchanger for the extraction of trivalent lanthanides from aqueous solution is well-established (2). This family of extractants combines the versatility of cation exchange resins with the ease and speed of solvent extraction. The work of Markovits and Choppin (3) suggests that dialkylnaphthalenesulfonic acids extract lanthanides by a micellar m e c h a n i i involving one micelle per extracted lanthanide ion at concentrations somewhat higher than lo4 (critical-micelle concentration for sister compound HDNNS in benzene). This assumption is supported by Chiarizia, Danesi, Raieh, and Scibona (4), whose results also suggest that little selectivity in extraction should be seen among the trivalent lanthanides. To achieve differentiation in extraction of the lanthanides, the crown ether, 4-tert-butylcyclohexyl-15-crown-5 (15-C-5) was intxoduced as a potential synergistic agent. A synergistic agent is a substance that in combination with another extractant c a w the distribution of the metal ion in the organic phase to be greater than the s u m of the distribution of the individual compounds. Crown ethers are macrocyclic polyethers that are known to complex with metal cations; the strength of association appears to be greater when the ionic radius of the cation corresponds to the cavity size of the crown (5). McDowell, Case, and Aldrup (6) have theorized that 0 1986 American Ckmlcal Society
ANALYTICAL CHEMISTRY, VOL. 58,NO. 8, JULY 1986
including crown ethers in solution with an organic soluble/ aqueous insoluble cation exchanger (such as HDDNS) would allow cation exchange followed by size-selective interaction with the crown ether. This work couples the excellent liquid-liquid cation exchange qualities of HDDNS with the size selectivity of the crown ethers, which for all their selectivity are poor cation exchangers because of the difficulty of anion transfer, necessary to preserve electrical neutrality, into the organic layer. Extractions of Ce(III), Pm(III), Eu(III), Tm(II1) by HDDNS/toluene and by HDDNS/l5-C-B/toluene from 0.5 M NaClO,, pH 2.0, a t 25 "C are reported.
EXPERIMENTAL SECTION Reagents. The tert-butylcyclohexyl-15-crown-5was obtained from Parish Chemicals and used without further purification. The radioisotopes of '%e, 14'Pm, lazl&rEu,and m @ 71' l were obtained from New England Nuclear. The HDDNS was obtained from King Industries and was purified by methanol extraction. The HDDNS/toluene solution was standardized by a potentiometric titration using 0.1 M NaOH in a 50150 ethanol/water solution. All other chemicals used were reagent grade or better. Procedure. The aqueous phase for this study contained 0.50 M NaC10, as the inert electrolyte with the pH adjusted to 2.0 with HClO,. The standardized HDDNS stock solution was converted to the NaDDNS by preequilibrating it with 0.50 M NaC104, pH 2.0. This preequilibration was done to ensure that no mass transport other than the one being investigated occurred during the experiment. The NaDNNS solutions used were prepared by volumetric dilution of the preequilibrated standardized stock solutions with toluene. The 0.5 M solution of NaC10, (aqueous) was made by diluting a 2.88 M stock solution, which was standardized by a cation ion exchange method. The 0.5 M NaC10, was adjusted to pH 2.0 with HClO,; the pH was defined as the -log [H+]by a solution of 1.OOO >: M HClO, in 0.50 M NaC104. A two-phase system of 3.00 mL of the preequilibrated HDDNS in toluene and of 3.00 mL of 0.5 M NaC10, at pH 2.0 was sealed in screw-cap vials and spiked with a lanthanide metal tracer (-3.0 >: lo4 dpm). The vials were placed on a rotary paddle (12 rpm) in a constant-temperature bath and mixed overnight at 25.0 A 0.1 "C. Equilibrium was found to be established after 6 h; longer contact times were a matter of convenience. Phases were then separated; the pH of the aqueous phase was measured; and 0.500-mL aliquots of each phase were assayed for j3 activity by liquid scintillation counting technique using Scinti-Verse11(Fisher Scientific) cocktail. Samples were counted for sufficient time so that the statistical uncertainty was Ce > Pm > Tm. Each metal studied exhibited a slope of 1, supporting the proposed micelle extraction mechanism whereby each metal is extracted by one micelle with an aggregation number greater than 3 (3). The effects of the addition of 15-C-5 to the extraction system are seen in Figure 1. As the concentration increases, a marked synergistic effect is seen. The extraction of Pm(II1) is enhanced by 50%, while the extractions of Ce(II1) and Eu(II1) increased 25% and 2070, respectively. The heaviest of the lanthanide ions, Tm(III), showed only a small effect. At concentrations of 15-C-5 greater than 1.00 X lo-, M, a
ANALYTICAL CHEMISTRY, VOL. 58, NO. 8, JULY 1980
1816
Table 11.
Separation Factors
and Ionic Stage' separation factor'
metal
ion(II1)
ionic radii,b nm
HDDNS alone
15-C-5
0.101 0.097 0.094 0.088
2.18
2.59 2.71 2.67
Ce Pm Eu Tm
"[HDDNS] = 5.30
1.95 2.46
M and [15-C-5] = 1.07
X
X
lo4.
Separation factor = D, f DEu.
Reference 8.
l 0)
c1
%
I
I
g i LEGEND
3= 0= A = 7 =
Ce(ti!) Pm Ill) h(lh
similarity between ionic radius and mean 15-C-5 radius. The relationship between mole ratio of crown ether to NaDDNS and synergistic activity is shown in Figure 2. Apparently, small additions of 15-C-5 enhance extraction and induce a degree of selectivity to that extraction. This synergistic effect has a limit, however, above which further addition of 15-C-5 actually causes marked deenhancement. One explanation for the synergistic effect is the incorporation of the crown into the DDNS micelles, thereby making the inclusion of cations into the micelle and its stabilization more selective. Evidence for this explanation was obtained by holding the concentration of 15-C-5 constant at 1.0 X M, where the maximum synergistic effect was observed, and varying the concentration of NaDDNS. A slope of unity was observed for plots of log D vs. log [NaDDNS], indicating that the micelle extraction mechanism was still operating. Figure 2 shows that the maximum synergistic effect occurs at approximately 20% 15-C-5, a ratio of 4:l NaDDNS to 15-C-5. The deenhancement of the extraction by 15-C-5 occurs a t lower ratios, and it is possible that as more crown ether is available to work with the micelles, the basic micellar mechanism providing cation exchange is disrupted. Interactions of the 15-C-5 molecules with the micelles, either blocking the approach of the metal ion into the micelle or actually breaking up the micelle, are logical explanations for the deenhancement observed. Further studies in this area are necessary to better understand the synergistic mechanism.
ACKNOWLEDGMENT
-m(ll!)
We thank W. J. McDowell of the Chemistry Division of Oak Ridge National Laboratory for helpful discussions concerning this work. Registry No. HDDNS, 40038-00-4; 15-C-5,102235-29-0;Ce, 7440-45-1;Pm, 7440-12-2; Eu, 7440-53-1;Tm, 7440-30-4.
LITERATURE CITED 23
10 c
20 0
30 0
40 0
50 0
Mole % 15-Crown-5 Figure 2. Variation of the synergistic factor with mole % 15-crown-5.
deenhancement of the extraction occurs with all metals being similarly affected. The separation factors for Ce, Pm, and Eu with T m are contained in Table 11. There is an increase in each separation factor with Pm(II1) showing the greatest increase. T o understand the marked synergistic effect on Pm, Ce, and Eu, a comparison of ionic radius to 15-C-5 radius is in order. Pederson and Frensdorff have reported a hole radius for 15C-5 of 0.085-0.11 nm (7). As can be seen in Table 11, Pm(II1) has an ionic radius of 0.097 nm, closest of all isotopes studied to the mean cavity size of 0.098 nm. Ce(II1) and Eu(II1) have correspondingly close ionic radii. Tm(III),with an ionic radius of 0.088 nm, is very close to the smallest value for the crown's radius. Thus, the synergistic effect seems to involve a close
Choppin, G. R. Radiochim. Acta 1983, 32, 43-52. Khophar, P. K.;Narayanankutty. P. J . Inorg. Nucl. Chem. 1968, 30, 1957- 1962. Markovits G. Y.; Choppin, G. R. In Ion Exchange and Solvent Extraction; Markinsky, J. A., Marcus, Y., Eds.; Marcel Dekker: New York, 1973; Vol. 3, pp 51-81. Chiarizla, R.; Danesi, P. R.; Raieh, M. A.; Sclbona, C. J . Inorg. Nucl. Chem. 1975, 3 7 , 1495-1501. Kinnard, W. F.; McDowell, W. J.; Shoun, R. R. Sep. Sci. Technol. 1980. 15. 1013-1024. McDdwell; W. J.; Case, G. N.; Aldrup, D. W. Sep. Sci. Technol. 1983. 18, 1483-1507. Pederson, C. J.; Frensdorf, H. J. Angew. Chem., Int. Ed. Engl. 1972, I f , 20-21. Shannon, R. D. Acta Crystallwr ., Sect. A : Cryst. Phys. Diffr. Theor. Gen. Crystallogr. 1978, A32, 751-758.
RECEIVED for review December 24,1985. Accepted March 17, 1986. Research was sponsored by the Division of Chemical Sciences, Office of Basic Energy Sciences, U S . Department of Energy, under Contract DE-AS05-79ER10489 with Tennessee Technological University.
