Metal Ion Separations with Lariat Ether Ion-Exchange Resins

Chapter 12

Downloaded by NORTH CAROLINA STATE UNIV on December 31, 2017 | http://pubs.acs.org Publication Date: February 11, 1999 | doi: 10.1021/bk-1999-0716.ch012

Metal Ion Separations with Lariat Ether IonExchange Resins 1

Richard A. Bartsch and Takashi Hayashita

Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-1061

Condensation polymerization of proton-ionizable dibenzo lariat ethers with formaldehyde in formic acid produces lariat ether ion-exchange resins. These novel, dual-function, cation-exchange resins have both cyclic polyether units and ion-exchange sites for metal ion complexation. This combination provides metal ion sorption selec tivities which are unattainable with ordinary ion-exchange resins. Structural variations within the proton-ionizable lariat ether monomers influence both the selectivity and efficiency of metal ion sorption. Three decades ago, Pedersen reported the first practical syntheses of a variety of macrocyclic polyethers, such as 1 and 2 (Figure 1), as well as the results of initial investigations of their metal salt complexation behavior (7,2). Pedersen proposed that an appropriately sized metal cation could be complexed within the central cavity of the macrocycle. The class name of "crown ethers" was advanced due to the resemblance of such complexes to crowns worn on the heads of royalty.

1

2

Figure 1. Structures of the crown ethers dibenzo-18-crown-6 (1) and benzo-15crown-5 (2). Pedersen also proposed a trivial nomenclature system for crown ether compounds (i) which is in widespread use today. The system consists of naming in order: (a) the number and kind of substituents on the polyether ring; (b) the total Current address: Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-77, Japan. ©1999 American Chemical Society

Bond et al.; Metal-Ion Separation and Preconcentration ACS Symposium Series; American Chemical Society: Washington, DC, 1999.

183

184 number of atoms in the polyether ring; (c) the class name "crown"; and (d) the number of oxygens in the polyether ring. Thus compounds 1 and 2 are designated dibenzo18-crown-6 and benzo-15-crown-5, respectively.


Crown Ether Polymers

Due to the strong metal ion binding behavior of crown ethers, considerable attention has been focused upon their incorporation into polymers (3). Immobilization of crown ethers in polymers prevents loss of these relatively expensive compounds to mobile phases during separation processes and also alleviates their potential physiological activity (4). Formaldehyde-type condensation polymers of benzocrown and dibenzocrown ethers were studied by Blasius and co-workers in the mid-1970's to the early 1980's (5-9). The resins were usually synthesized by condensation of dibenzocrown ethers with formaldehyde in formic acid or of benzocrown ethers with formaldehyde and a crosslinking agent, such as phenol, resorcinol, or xylol, in a mixture of formic and sulfuric acids. Simplified structures for examples of such polymers are represented by 3 and 4 (Figure 2). The simplification is to represent the resin as a linear polymer, even though it is crosslinked to some degree. The formaldehyde-type crown ether polymers were found to be easy to synthesize and to have excellent resistance to heat and to acidic and basic environments. (Copolymer 3 is listed in current Aldrich and Fluka catalogs as poly(dibenzo-18-crown-6)-cc-formaldehyde and poly (dibenzo-18crown-6), respectively.)

3

4

Figure 2. Simplified structures for formaldehyde condensation polymers of dibenzo- and monobenzocrown ethers. Blasius and co-workers also investigated applications of the crown ether polymers in metal ion separation processes (5-9). For their use in chromatographic separations, sorption of a metal ion from solution onto the resin must be accompanied by concomitant transfer of an anion. Therefore, the selectivity and efficiency of metal ion sorption from solution by a crown ether polymer is strongly influenced by the identity of the anion(s) present in the solution. Proton-ionizable Lariat Ethers

Attachment of one or more side arms with potential metal ion coordination sites to a crown ether framework provides complexing agents known as "lariat ethers" (JO). In 1981, we reported the synthesis of the lariat ether carboxylic acid 5 (Figure 3) with a hydrogen attached geminal to the functional side arm on the polyether ring and its application in the solvent extraction of alkali metal cations from aqueous solutions into chloroform (//). In such proton-ionizable lariat ethers, a side arm with an acidic



185

Figure 3. Structures of lariat ether carboxylic acid (5) and Amberlite™ CG-50 (6), a commercially available, cation-exchange resin. group is attached to a crown ether ring (12) and metal ion complexation involves the ion exchange of a metal ion for the proton of the acidic function. Eliminating the need for concomitant transfer of an aqueous phase anion into the organic medium is of immense importance for applications of crown and lariat ether ligands as the next generation of selective metal ion extractants. For process solvent extraction of metal ions, the anions normally encountered are chloride, nitrate, and sulfate, which are very hydrophilic ions. The efficiency of metal ion extraction is markedly enhanced for proton-ionizable lariat ethers compared with analogous compounds which have nonionizable side arms (11,13). From examination of Corey-Pauling-Kortun (CPK) space-filling models, the cavity diameter of dibenzo-16-crown-5 is estimated to be 2.0-2.4 Â. For the alkali metal cations, the ionic diameters are: L i , 1.48 Â; Na , 2.04 À; K , 2.76 A; Rb , 2.98 Â; and Cs , 3.40 Â (14). Based upon the relationship between the relative diameters of the alkali metal cations and the polyether cavities in dibenzo-16-crown-5 compounds, such as 5, Na selectivity would be predicted. Attachment of a lipophilic alkyl group geminal to the functional side arm in 5 is beneficial for two reasons. First, introduction of the alkyl group enhances the overall lipophilicity of the extractant which decreases loss of the ionized lariat ether from the organic phase into a contacting basic aqueous phase during solvent extraction of metal ions (11,15). Second, the presence of an alkyl group geminal to the oxyacetic acid side arm enhances the Na selectivity in competitive solvent extraction of alkali metal cations (15). The enhancement in Na selectivity is proposed to arise from orientation of the alkyl group away from the polar polyether ring which positions the carboxylic acid group of the functional side arm directly over the crown ether cavity. Such preorganization of the binding site enhances the selectivity in metal ion complexation by macrocyclic ligands (16). In agreement, solid-state structures of lariat ether carboxylic acids 5 with a geminal hydrogen and a geminal decyl group have the oxyacetic acid group directed away from the polyether cavity in the former and over the cavity in the latter (17). +

+

+

+

+

+

+

+

Lariat Ether Ion-Exchange Resins

It was envisioned that formaldehyde-type condensation resins could be prepared from proton-ionizable dibenzo lariat ethers, such as 5. The resultant lariat ether ionexchange resins would have both ion-exchange and cyclic polyether binding sites for metal ion complexation. It was anticipated that such dual function cation-exchange resins (17) would provide metal ion sorption selectivities which are different from those attainable with ordinary ion-exchange resins.


186


Lariat Ether Carboxylic Acid Resins. Reaction of appropriate acyclic and cyclic dibenzo polyether carboxylic acid monomers with formaldehyde in formic acid at reflux produced the new polyether ion-exchange resins 7-14 (Figure 4) (19,20).

a

7

8 H 9

CH

3

C2H5 C3H7 C4H9

10 11

12 13

C6H13 C-10H21

14

Figure 4. Dibenzo acyclic polyether and lariat ether carboxylic acid resins. Alkali Metal Cation Sorption. The behavior of these resins was evaluated in competitive alkali metal cation sorption from aqueous solutions which were 0.10 M in each of the five alkali metal cations with a mixture of chloride and hydroxide counterions (19,20). In control experiments, it was shown that alkali metal cation sorption from such solutions was completed in a matter of minutes and that the sorbed metal ions could be readily stripped from the resins by washing with aqueous hydrochloric acid. For comparison with an ion-exchange resin which contained the same acidic function but no polyether unit, competitive alkali metal cation sorption was also performed with Amberlite™ CG-50 (6, Figure 3), a commercially available poly(methacrylic acid) resin. For CG-50, the selectivity for alkali metal cation sorption from neutral and alkaline solutions was L i > Na > K ~ Rb « Cs . For acyclic polyether carboxylic acid resin 7, the sorption selectivity was L i > Na > K > Rb « Cs* (Figure 5a) which shows that the introduction of ether linkages does not significantly alter the sorption selectivity from that found with CG-50 (19). On the other hand, the sorption selectivities for the lariat ether ion-exchange resins 8 and 11 were Na > L i « K > Cs > Rb (Figure 5b) and Na » Li > K « Cs > Rb (Figure 5c), respectively. Thus the L i sorption selectivity exhibited by CG-50 (6) and the acyclic polyether carboxylic acid resin 7 changed to Na sorption selectivity for the lariat ether carboxylic acid resins 8 and 11. Although both lariat ether carboxylic acid resins 8 and 11 exhibit Na selectivity, that for resin 11, in which a propyl group is attached to the same crown etherringcarbon as the oxyacetic acid side arm, is much higher than that for resin 8. Examination of CPK space-filling models reveals that when the propyl chain in the binding unit of resin 11 points away from the polar crown ether ring, the carboxylic acid group is positioned directly over the crown ether cavity. This preorganizes the binding sites in resin 11 compared with those in resin 8. Such preorganization of the binding sites enhances complexation of that metal ion that best fits the cavity (16). This was the first instance in which the conformational positioning of the ion+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+



187

2

6

10

2

6

10

2

6

10

Equilibrium pH

Figure 5. Competitive alkali metal cation sorption by lariat ether carboxylic resins (a) 7, (b) 8, and (c) 11: L i (Δ), Na (O), K (•), Rb (A), Cs ( · ) . +

+

+

+

+

exchange group in an ion-exchange resin has shown an important influence upon metal ion recognition. Lariat ether carboxylic acid resin 11 also was utilized for the selective column concentration of alkali metal cations from dilute, basic aqueous solutions (20). Due to a stronger interaction of Na with the resin, the elution peak for Na in the acidic stripping solution was retarded relative to those for the other alkali metal cations. With gradient stripping, the concentration factor for Na from a basic aqueous sample solution, which was 6.0 X 10' M in each of the five alkali metal cations, reached 1030 with an 84% purity (20). The influence of the geminal alkyl group on selectivity and efficiency of competitive alkali metal cation sorption was further probed with the series of lariat ether carboxylic acid resins 9-14 (21). In this series, there is systematic structural variation of the geminal n-alkyl group from one to ten carbons. The highest metal ion loading and Na selectivity were obtained when the geminal alkyl group was methyl, ethyl, or propyl. Longer alkyl groups were found to be detrimental to both the sorption efficiency and selectivity. The effect of medium polarity on competitive sorption of alkali metal cations from aqueous and aqueous methanolic solutions by polyether carboxylic acid resins 714 was investigated (22). For the lariat ether carboxylic acid resins 8-14, the Na selectivity was enhanced as the percentage of methanol in the medium increased. This +

+

+

5

+

+


188

was attributed to strengthened metal ion-crown ether interactions as the solvent polarity decreased. The next structural variation was to determine the influence of the crown ether ring size upon the selectivity of alkali metal cation sorption for the series of dibenzo polyether carboxylic acid resins 7 and 15-17 (Figure 6) (23). Once again, the lariat ether carboxylic acid resins were found to exhibit enhanced sorption selectivity over the corresponding acyclic polyether carboxylic acid resins. G o o d sorption selectivity for L i and N a over K , R b , and C s was observed for the dibenzo-14-crown-4 carboxylic acid resin 17 which has a geminal propyl group. This change from the very good N a sorption selectivity observed earlier with the dibenzo- 16-crown-5 carboxylic acid resin 11 to sorption selectivity for L i and N a with the corresponding dibenzo-14-crown-4 resin 17 is attributed to the smaller crown ether ring size in the latter. F o r column concentration of alkali metal cations from dilute, basic aqueous solutions, gradient elution of the sorbed metal ions from resin 17 with aqueous acid gave selective column concentration of L i and N a from a solution of the five alkali metal cation species. +

+

+

+

+


+

+

+

+

+

17 C H 3

Figure 6. A c y c l i c and cyclic dibenzo polyether carboxylic acid resins. Polymer imprinting in which a template metal ion is present during polymerization is currently receiving considerable attention (24). The possibility of enhancing the sorption selectivity for crown ether carboxylic acid resins by template polymerization was examined by synthesizing resins 8 and 11 in the presence of one equivalent of alkali metal salt (25). Surprisingly, it was observed that the presence of certain alkali metal cations markedly reduced polymer formation. The alkali metal cation that provides the best fit for the crown ether cavity produced the largest decrease in polymer yield. It was proposed that metal ion complexation rendered the dibenzocrown ether monomer inert to polymerization under the reaction conditions and only uncomplexed monomer was involved in polymer formation. In agreement, no template effect for alkali metal cation sorption was noted for the polymers which were produced (25).

Alkali and Alkaline Earth Metal Cation Sorption. Batch sorption of the four physiological metal ions N a , K , M g , and C a ^ by C G - 5 0 (6), acyclic dibenzo polyether carboxylic acid resin 7, and lariat ether carboxylic acid resins 8 and 11 was also investigated (26). The aqueous solutions were 0.10 M in N a and K and 0.050 M in Mg and C a . The observed sorption selectivity order for C G - 5 0 +

+

2 +

+

+

+

2 +

2 +

2 +

+

+

was C a > Mg » N a ~ K . (Preferential sorption of the divalent metal ions results from enhanced electrostatic interaction with the carboxylate groups of the resin.) When the aqueous solution p H was 6-8, the sorption selectivity order for acyclic polyether carboxylic acid resin 7 and lariat ether carboxylic acid resin 8


189

2 +

2 +

+

+

changed slightly to C a » M g > N a ~ K . For lariat ether carboxylic acid resin 11, which has a geminal propyl group, the sorption selectivity was found to be p H dependent. A t p H = 6, the sorption selectivity order was N a > C a > M g ~ K ; whereas at p H = 8, it was C a > N a > M g > K . Constraint of the ion-exchange group in resin 11 to a position which is highly favorable for N a complexation allows sorption of this alkali metal cation to compete favorably with that of the alkaline earth metal cations. +

2 +

+

2 +

2 +

2 +

+

+

+

Chromatographic Separation of Y

3 +

2+

from Sr . Separation of Y

3 +

and


2

Sr * is important for the determination in environmental samples of the fission product S r and its daughter Y (27). Extraction of pure Y from its precursor S r is also important for applications in nuclear medicine (28). Column chromatographic separation of Y and S r (each 2.5 X 10" M)from aqueous solutions by sorption on lariat ether carboxylic acid resins 8 and 11 has been reported (29). With both resins, S r was cleanly separated from the mixture of Y and S r . The separation of S r was more effective with resin 8 which shows that in this case the presence of a geminal propyl group was detrimental.

9 0

9 0

3 +

9 0

2+

9 0

3

2 +

3 +

2 +

2 +

Lariat Ether Phosphonic Acid Monoethyl Ester and Lariat Ether Sulfonic Acid Resins. T o enhance the acidity of the ion-exchange site in the lariat ether ion-exchange resins, acyclic and cyclic dibenzo polyether phosphonic acid monoethyl ester monomers and analogous sulfonic acid compounds were polymerized with formaldehyde in formic acid to provide lariat ether phosphonic acid monoethyl ester resins 18-23 and 27 and lariat ether sulfonic acid resins 24-26 (Figures 7 and 8) (Laney, Ε . E . ; Lee, J. H . ; K i m , J. S.; Huang, X . ; Jang, Y . ; Hwang, H . - S . , Hayashita, T . ; Bartsch, R. A . React. Funct. Polym., 1998, in press).

H.X>CH lj>OH 2

OC H

f ^ l

2

5

OC H

f^]

2

5

ex.

? τ CH3 CH3

R

18

19 Η 20 C H

3

21 C3H7 Figure 7. Acyclic and cyclic dibenzo polyether phosphonic acid monoethyl ester resins.

Alkali Metal Cation Sorption. Competitive sorption from aqueous solutions which were 0.10 M in each of the five alkali metal cations by acyclic polyether phosphonic acid monoethyl ester resin 18 and the dibenzo- 16-crown-5 phosphonic acid monoethyl ester resins 19 and 20 was investigated (30). The sorption selectivity order for the acyclic polyether resin 18 was L i

+

> K

+

+

~ Rb ~ Cs

+

> N a . F o r the lariat ether phosphonic acid monoethyl ester 19, the ordering changed +

+

+

to L i > N a > K

+

+

+

+

> R b ~ C s . The change in the position for N a in the sorption

selectivity ordering from last with resin 18 to second with resin 19 is consistent with


190

H^O(CH ) fOH f*^ OC H 2

H

3

2

0(CH ) fOH 2

3

OC H 2

5

5

(X •CH2-


CH3 CH3 23

22

H ^(CH ) S0 H v

2

3

R>^(CH ) S0 H 2

3

3

3

-CH2-

CH3 CH3 R

24

25 Η 26

C H 3

7

OC2H5

C5 Λ_/ 27

Figure 8. Acyclic and cyclic dibenzo polyether phosphonic acid monoethyl ester resins 22, 23 and 27 and acyclic and cyclic dibenzo polyether sulfonic acid resins 24-26. an enhanced role of the cyclic polyether unit in metal ion binding by the latter. For lariat ether resin 20, which has a geminal methyl group, the sorption selectivity was found to depend upon the pH of the aqueous solution from which the alkali metal cations were sorbed. For pH 3-6, the sorption selectivity order for resin 20 was Na > L i > K ~ Rb « Cs ; and for pH > 8, the ordering became L i > Na > K - Rb Cs . Although Na sorption was enhanced by the presence of the geminal methyl group in resin 20 compared with resin 19, resin 20 remained L i selective over much of the pH region. Thus the sorption selectivity for resin 20 is found to be quite different from the very good Na sorption selectivity observed for the analogous dibenzo-16-crown-5-oxyacetic acid resin 9 and suggests stronger interactions of L i with a phosphonic acid monoethyl ester group than a carboxylic acid function. +

+

+

+

+

+

+

+

+

+

+

+

+

+


191 Sorption of Divalent Heavy and Transition Metal Cations. The ability of proton-ionizable lariat ether resins to sorb heavy and transition metal cations from acidic aqueous solutions has been investigated (Laney, Ε. E.; Lee, J. H.; Kim, J. S.; Huang, X.; Jang, Y.; Hwang, H.-S., Hayashita, T.; Bartsch, R. A. React. Funct. Polym., 1998, in press). In the initial screening study, competitive batch sorptions of 1.0 mM Pb and Zn from aqueous solutions of pH 0-3 with a shaking time of four hours was examined for three series of acyclic and cyclic polyether resins with proton-ionizable groups. Under these conditions, CG-50 (6), a poly(methacrylic acid) resin, and Rexyn 101(H), a poly(vinylsulfonic acid) resin, exhibited no selectivity in competitive sorption of Pb and Zn . The three series of resins included the polyether carboxylic acid resins 7, 8, and 11, polyether phosphonic acid monoethyl ester resins 18, 19, and 21-23, and the polyether sulfonic acid resins 24-26. The polyether sulfonic acid resins 24-26 have longer spacers between the acidic function and the polyether unit than do the lariat ether carboxylic acid resins 7, 8, and 11 and the lariat ether phophonic acid monoethyl ester resins 19 and 21. Therefore, the lariat ether phosphonic acid monoethyl ester resins 22 and 23, which have the same spacer unit as those in the lariat ether sulfonic acids, were also examined. For competitive sorption of Pb and Zn at pH = 2 or lower, the three polyether carboxylic acid resins 7, 8, and 11 exhibited poor metal ion loading. With the three polyether sulfonic acid resins 24-26, both Pb and Zn were completely sorbed at pH = 2 or less. With pH < 2, only very slight selectivity for Pb sorption was noted. In the region of pH = 1.0-2.5, both acyclic polyether phosphonic acid monoethyl ester resin 18 and the lariat ether phosphonic acid monoethyl ester resin 19 gave good selectivity for Pb over Zn with complete sorption of the Pb at pH = 2.5. In contrast, lariat ether phosphonic acid monoethyl ester resin 21 gave poor metal ion loading, but with some selectivity for sorption of Pb . For the phosphonic acid monoethyl ester resins 22 and 23, which have longer spacer units in the side arm than do resins 18 and 19, sorption efficiency was intermediate with good selectivity for sorption of Pb over Zn . From this screening study, it was concluded that the structural features that promote selective Pb binding by proton-ionizable dibenzo-16-crown-5 resins are: (a) a cyclic polyether unit; (b) a proton-ionizable group of intermediate acidity; (c) a short spacer unit connecting the acidic group to the polyether framework; and (d) the absence of a geminal alkyl group. Based upon these results, dibenzo-16-crown-5 and dibenzo-19-crown-6 phosphonic acid monoethyl ester resins 19 and 27, respectively, were selected for more intensive study (31). For single species Pb sorption by resin 19, it was determined that the sorption complex involved one polyether unit, a Pb cation, and a monovalent anion from the aqueous solution. Single species sorption experiments showed that Pb binding by the dibenzo- 19-crown-6 phosphonic acid monoethyl ester resin 27 was somewhat stronger than that that for the dibenzo-16-crown-5 phosphonic acid monoethyl ester resin 19 (Figure 9). However, the monomer precursor to resin 19 is much easier to prepare than that for resin 27 which is an important compensating factor. For the expanded studies of competitive metal cation sorption by lariat ether phosphonic acid monoethyl ester resins 19 and 27, a broader pH region of 0-6 was utilized. For competitive batch sorption of Pb and a second multivalent metal ion species, both resins 19 and 27 were found to exhibit good sorption selectivity for Pb over Cd , Ni , Zn , and Fe in certain acidic pH regions. The influence of the presence of large excesses of alkali metal cations and two of the alkaline earth metal cations upon the Pb sorption efficiency was also examined. Efficient sorption of 1.0 mM Pb by resins 19 and 27 was maintained even for aqueous solutions which contained 0.20 M alkali metal cations. For resin 27, efficient Pb sorption from solutions containing 0.10 M Mg and Ca was observed. 2+

2+


2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

2+

3+

2+

2+

2+

2+

2+



192

I

1

1

1

1

1

1

0

1

2

3

4

5

6

Equilibrium pH 2+

Figure 9. Non-competitive Pb sorption by lariat ether phosphonic acid mono ethyl esters 19 (O) and 27 (•). Summary Condensation polymerization of proton-ionizable dibenzo lariat ethers with formaldehyde in formic acid produces novel ion-exchange resins. These lariat ether ion-exchange resins have both ion-exchange and cyclic polyether binding sites for metal ion complexation and provide sorption selectivities which cannot be obtained with ordinary ion-exchange resins. From sym-(alkyl)dibenzo-16-crown-5-oxyaeetic acid monomers, new resins have been prepared which exhibit very good Na selectivity in alkali metal cation separations by both batch sorption and concentrator column methods. Conformational positioning of the ion-exchange group over the polyether unit is shown to have an important influence on the recognition of alkali metal cations. A resin prepared from syra-dibenzo-16-crown-5-oxyacetic acid monomer has been used to separate Y from Sr . Proton-ionizable lariat ether resins with phosphonic acid monoethyl ester groups are found to exhibit good sorption selectivity for Pb from acidic aqueous solutions over a variety of multivalent heavy and transition metal cations, as well as large excesses of alkali and alkaline earth metal cations. +

3+

2+

2+

Acknowledgment This research was supported by the Division of Chemical Sciences of the Office of Basic Energy Sciences of the U.S. Department of Energy (Grant DE-FG03-9414416) and the Texas Higher Education Coordinating Board Advanced Research Program. Literature Cited (1) (2) (3) (4)

Pedersen, C. J. J. Am. Chem. Soc. 1967, 89, 2495. Pedersen, C. J. J. Am. Chem. Soc. 1967, 89, 7017. Smid, J.; Sinta, R. Top. Curr. Chem. 1984, 121, 105. Hiraoka, M . Crown Compounds: Their Characteristics and Applications; Elsevier: New York, NY, 1982; Ch. 7.


193 (5)

Ε . ; Adrian, W . ; Janzen, K . P.; Klauthe, G .

J. Chromatogr. 1974,

(6) (7) (8)

Blasius, 89. Blasius, Blasius, Blasius,

(9) (10)

Blasius, E.; Maurer, P. J. Chromatogr. 1976, 125, 511. G o k e l , G . W . ; Dishong, D . M.; Diamond, C . J . J. Chem.

96,

E.; Janzen, K . P. Top. Curr. Chem. 1981, 98, 165. E.; Janzen, K . P. Pure Appl. Chem. 1982, 54, 2115. E.; Janzen, K . P.; Keller, M.; Lander, H.; Nguyen-Tien, T . ; Scholten,

G . Talanta 1980, 27, 107. Soc., Chem.


Commun. 1980, 1053. (11) (12) (13)

Strzelbicki, J.; Bartsch, R. A. Anal. Chem. 1981, 53, 1894. Bartsch, R. A. Solvent Ext. Ion Exch. 1989, 7, 829. Bartsch, R. Α . ; Hayashita, T . ; Lee, J . H.; K i m , J . S.; Hankins,

M.

G.

Supramol. Chem. 1993, 1, 305 (14)

(15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31)

M c B r i d e , D . W . ; Izatt, R. M.; L a m b , J . D . ; Christensen, J . J. In Inclusion Compounds; Atwood, J. L.; Davies, J. E. D . ; M c N i c o l , D . D . Eds.; Academic Press: New Y o r k , NY, V o l . 3; p 586. Walkowiak, W . ; Charewicz, W . Α . ; Kang, S. I.; Yang, I.-W.; Pugia, M. J.; Bartsch, R. A. Anal. Chem. 1990, 62, 2018. C r a m , D . J . Angew. Chem., Int. Ed. Engl. 1986, 25, 1039. Bartsch, R. Α . ; K i m , J . S.; Olsher, U.; Purkiss, D . W . ; Ramesh, V . ; Dalley, Ν . K . ; Hayashita, T . Pure Appl. Chem. 1993, 65, 399. Alexandratos, S. D . ; Wilson, D . L. Macrocycles 1986, 19, 280. Hayashita, T . ; G o o , M.-J.; Lee, J . C.; K i m , J . S.; Krzykawski, J . ; Bartsch, R . A . Anal. Chem. 1990, 62, 2283. Hayashita, T . ; Lee, J. H.; Chen, S.; Bartsch, R. A . Anal. Chem. 1991, 63, 1844. Hayashita, T . ; G o o , M.-J.; K i m , J. S.; Bartsch, R. A . Talanta 1991, 38, 1453. Hayashita, T . ; Lee, J. H.; Lee, J . C.; Krzykawski, J . ; Bartsch, R. A. Talanta 1992, 39, 857. Hayashita, T . ; Lee, J. H.; Hankins, M. G.; Lee, J. C.; K i m , J. S.; Knobeloch, J. M.; Bartsch, R. A. Anal. Chem. 1992, 64, 815. Wulff, G . Angew. Chem., Int. Ed. Engl. 1995, 34, 1812. Zhao, Q.; Bartsch, R. A. J. Polym. Sci., Polym. Chem. 1995, 33, 2267. Hayashita, T . ; Bartsch, R. A. Anal. Chem. 1991, 63, 1847. W i l k e n , R. F.; Joshi, S. R. Radioact. Radiochem. 1991, 2, 95 Srivistava, S. C . Radiolabeled Monoclonal Antibodies for Imaging and Therapy; Plenum: N e w Y o r k , NY, 1988. W o o d , D . J . ; Elshani, S.; W a i , C . M.; Bartsch, R. Α . ; Huntley, M.; Hartenstein, S. Anal. Chim. Acta 1993, 284, 37. Hankins, M. G., Doctoral Dissertation, Texas Tech University, 1994, pp. 41-59 Laney, Ε . E., Doctoral Dissertation, Texas Tech University, 1994, pp. 73173


Metal Ion Separations with Lariat Ether Ion-Exchange Resins

Recommend Documents