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Water-eluent based Ion Chromatography on Silica Bonded Molecular Baskets
Water-eluent based Ion Chromatography on Silica Bonded Molecular Baskets
J. D. Glennon*, B. Lynch, K. Hall, S.J. Hanis and P. O'Sullivan.
DEPARTMENT OF CHEMISTRY.
UNIVERSITY COLLEGE CORK, CORK, IRELAND.
1 ABSTRACT
The retention behaviour of alkali and alkaline earth metal ions on a novel silica bonded macrocyclic calix[4larene tetradiethylamidephase is reported using water-eluent based ion chromatography. Using.a shofl column and water as the mobile phase, the silica bonded phase displays enhanced chromatographicselectivitiesfor Ca2' and S?' over and Ba2' and for Na' over K , Cs' and Li' in line with known complexation selectivity ' from stability constant and extraction data. Selected ternary mixrureS of alkali and alkaline earths can be separated with the elution order Ca2'/Na' >> K ' >' ! g M using water modified with methanol or acetonitde as the mobile phase.
M2'
2 INTRODUCTION
Synthetic macrocyclic compounds known as calixarenes, have the ability, when suitably functionalised. to act as molecular baskets for binding ionic guests. The hostguest interactions of free calix[nlarenes with a variety of neutral and ionic species have been widely reported. While analogies could be drawn with crown ethers or cyclodextxins, the calixarenes are chemically quite unique. Calix[n]arenes are cyclic oligomers composed of phenolic units linked by methylene bridges at positions ortho to the hydmxyl groups. These compounds may contain four to eight aryl moieties arranged in a macrocyclic array with a central cavity.' Derivatisation of the phenolic groups has produced a variety of functionalised calixarenes which show selective ionophoric pmpetties towards selected guest species. The host-guest complexation is determined by the overall macrocyclic structure, most importantly by the cavity size but also by the nature of the functional groups which act as the binding sites. The ionophoric properties of functionalised calixarenes have been clearly demonstrated using NMR spectroscopy and by liquid-liquid extraction studies. Specifically, the conversion of p-ferf-butylcalix[4larene and p-ferf-butylcalix[6lareneinto acetic esters, ketones and amides results in ionophoric activity.2 The phase transfer
154
Progress in Ion Exchange: Advances and Applications
activity of these functionalised calixarenes has been demonstrated for the extraction of metal picrates from water into di~hloromethane.~ Tetrameric calixarene esters, ketones and amides show a selective ability to extract Na+ while the hexameric c a l h n e s have higher efficiencies for Cs+ ions. As with crown ethers, the selective complexation properties of calixarenes have been successfully exploited in the construction of ion selective electrodes4*5and in the development of chemically modified voltammetric sensors.6 However, only recently have applications in chromatography appeared in the literature. Specifically, water soluble calixarenes have been shown to be effective as selectivity modifiers in chromatography and capillary electrophoresis. In particular, the water soluble calix[6]arenepsulphonate has been used in the modification of selectivity for substituted phenols in capillary electrophoresis' and reversed phase liquid chromatography.' Our laboratory has concentrated on the development of novel solid phase materials incorporating functionalised calixarenes, with applications in ion separation and analysis. Solid phase extraction cartridges. incorporating chelating molecular baskets immobilised onto XAD or silica, have been used to sequester metal ions from aqueous s o l ~ t i o n .The ~ quantitative trace enrichment of Cu2+, Zn2+, and Mn2+ from water samples prior to ion chromatographic analysis has been demontrated using immobilised calix[4]arene tetrahydmxamate. The separation of alkali and alkaline earth ions on chemically bonded crown ether stationary phases, using simple water-methanol mobile phases, has previously been r e p ~ r t e d . ~ OThe - ~ ~application of silica bonded calixarene phases in watereluent based ion Chromatography offers exciting possibilities, in view of the established tailoring of selectivity for these ions that is possible through lower rim functionalisation. A silica bonded calix[4]arene tetraester phase has been shown to have e n h a n d chromatographic selectivity for Na+ over other alkali metal ions.l3 In this paper, the use of the silica bonded tetrameric calixarene tetradiethylamide phase for water-eluent based ion chromatographic separation of alkali and alkaline earth metal ions is reported.
3 EXPERIMENTAL Chemicals and reagents.
Silica (Nucleosil, 5pm particle size) was purchased from Macherey-Nagel (Diiren, Germany). HPLC grade methanol and acetonitrile and AnalaR grade toluene were purchased from Merck, (Darmstadt, Germany). All alkali metal salts were AnalaR grade from BDH (Poole. UK). Instrumentation.
For water-eluent based ion chromatography, the system consisted of a Dionex series 4000i metal free pump and injection system, plumbed with PTFE tubing. The injection was pneumatically driven, with a loop volume of 25 pl, unless otherwise stated. The conductivity detector used was a Dionex CDM I1 utilising a Dionex conductivity cell (8 pl volume) and incorporating temperature compensation facilities. Empty stainless steel columns ( 4.5 cm x 4.6 mm i.d.) were slurry packed with the silica bonded calix[4]arene tetraamide phase. An Elgastat water purification system provided water for ion
Ion Chromtography and Electrophoresis
155
chromatography with a resistivity greater than 15Mohm cm. Synthesis of the silica bonded calixI4larene tetradiethylamide phase p-Allylcalix[4]arene was prepared according to the reported procedure' and was converted into its ethyl acetate derivative by refluxing with ethyl bromoacetate in acetone in the presence of anhydrous potassium carbonate as described p r e v i o ~ l y . ~p Allylcalix[4larene tetraacid was treated with oxalyl chloride to afford pallylcalix[4]arene tetraacid chloride, which on treatment with N.Ndiethylamine in tetrahydrofuran was converted to the diethylamide. This pallylcalix[4larene derivative was treated with mercaptopropyl-triethoxysilane at 7OoC for one hour in the presence of cumene hydroperoxide (free radical source for thiolene addition) to yield the triethoxysilane derivative. The silica immobilised caliix[4]arene tetradiethylamide shown in Figure 1, was prepared by refluxing ca. 0.32 g of the triethoxysilyl derivative of the calix[4]arene in 30 ml toluene with 2.0 g of activated Nucleosil for 24 hr. The silica bonded phase was filtered, washed with ca. 100 ml toluene and yielded 6.7% C on elemental analysis. Water-eluent based Ion Chromatography The chromatographic selectivity for alkali metal and alkaline earth metal ions was examined at mom temperature by injection of standard aqueous solutions, prepared in the concentration range from O.lmM - lOmM, onto the calix[rl]arene tetradiethylamide phase with water as the mobile phase. Injections of methanol were used to determine the value. Methanol or acetonitrile in different concentrations was added to the mobile phase and its influence on the retention determined. 4 RESULTS AND DISCUSSION The use of water or other polar solvents as the sole component of the mobile phase in ion chromatography, can eliminate the need for electrolytes, precise mobile phase make-up and ion suppression as part of conductivity detection. This water-eluent based ion chromatography is possible with electrolyte sorbing phases such as ionophoric crown ether phases. While the earliest results with crown ether phases gave broad peaks, excellent alkali metal ion separations were subsequently obtained in a matter of minutes with water as eluent.'0." In the present work, some of the first results obtained with silica bonded molecular baskets, constructed using functionalised calixarenes. are presented. Distinct features of these macrocyclic compounds, apart from their shape, is that very high ion selectivities are possible and that this selectivity can be modulated by suitable functionalisation of the lower rim of the calixarene. In earlier work, with silica bonded tetraethyl calix[4]arene tetraacetate, it has been shown that its Na' selectivity is transferable to silica bonded phases. From extraction and stability constant work, it has been shown that a similar tetrameric calixarene functionalised instead with diethylamide, exhibit, substantial complexation of alkaline earths in addition to Na'. It has the highest reported complexation selectivity for Ca2+ over Mg2+ for a neutral camer ionophore. l4 The structure of this silica bonded calix[4larene diethylamide, prepared from the triethoxysilane derivative, is given in Figure 1. Details of the characterisation of this
156
Progress in Ion Exchange: Advances and Applications
silica bonded phase by solid state NMR are to be presented elsewhere.
-Si-
I 0 --O-~i-O-CH~-CH3 I
Figure 1 Structure of the silica bonded calix[4larene diethylamide phase. In the present work using conductivity detection and with water only as the mobile phase, sodium ions are retained significantly longer than all the other alkali metal ions. While sharp peaks very close to the to are obtained on injections of LiCl, KCl and CsCl, NaCl has a different chromatographic behaviour, is retained and shows fronting. A mivtUre of 5mM NaCl and 5mM KC1 on injection yields close-to-baseliie resolution and a selectivity factor of 5. For alkaline earths, Ca2' and S?' are selectively retained, like Na', while M g ' and Ba2' elute close to to. Again close-to-baselime resolution is obtained on injection of a mixture of Ca2' and M g ' and while the quality of the separation obtained is reduced by broadening of the Ca2' peak, a selectivity factor of 14 is observed. If watedorganic modifier mixtures are utilised instead of pure water as the mobile phase, the retention times obtained for alkali and alkaline earths increase significantlywith the rise of organic fraction in the eluent. These increases are in proportion to the extent of complexation of the ion in the molecular basket. The most noticable feature is how little the retention of ~ g 2 ' varies, staying close to the to. These results are illustrated in Figure 2, where the capacity factors obtained for selected metal ions are plotted against % methanol and % acetonitrile. Acetonitrile is seen to be more effective than methanol at increasing ion retention. In Figure 3, a chromatogram obtained for a mixture of Ca?' and M 8 ' is given to illustrate the type of separation achieved.
157
Ion Chromatography and Electrophoresis
4.5 4
3.5 3
L 2.5 2 1.5 1 0.5 0
0
5
1
0
1
5
2
0
2
5
3
KM
0
5
1
0
1
5
2
0
2
5
0
3
5
4
0
4
0
a
3
0
3
6
K ACN
M2'
Figure 2 Variation of capacity factors for chloride salts of Na+, K+,Ca2+, and as a function of percentage organic modifier in the mobile phase. (concentration: 1mM)
Progress in Ion Exchange: Advances and Applications
158
,
'
.
.
.
L
0 1 2 3 4 5
TIME I MIN
figure 3 Chromatogram obtained on injectionof 5mM CaCl, and 5mM MgCl, on a silica bonded calix[4]arene diethylamide column (20% aqueous MeOH eluent, 1.0 mumin., conductivity detection). A typical chromatogram obtained on injection of a mixture of NaCl, KCl and MgCl, is given in Figure 4, using 20% aqueous acetonitrile.
Mg
K
0
5 10 15
TIME / MIN
Figure 4 Chromatogram obtained on injection of 1mM NaCl, 1mM KCl and 1mM MgCl,. (20% aqueous ACN eluent, 1.0 ml/min., conductivity detection.) 5 CONCLUSIONS Silica bonded calix[4]arene diethylamide stationary phases show selective retention of Na+ , S?+ and Ca2' ions over other alkali and alkaline earth ions injected, with pure
Ion Chromatography and Electrophoresis
159
water mobile phases. These new molecular recognition phases based on macrocyclic calixarenes show enormous potential for the tailoring of chromatographic selectivity thmugh calixarene functionalisation and the use of mobile phase additives. Further work is in progress on these versatile molecular basket sorbent phases for ion Separation and analysis.
ACKNOWLEDGEMENTS The authors wish to gratefully acknowledge the help and advice given by Professor M.A. McKervey, School of Chemistry, Queens University, Belfast. Thanks also to Ms. G. Flynn for work in the laboratory.
(1) C.D. Gutsche, 'Calixarenes', Vol 1 inMonographs in Supramolecular Chemktry, ed. J.F. Stoddart, Royal Society of Chemistry. 1989. (2) M.J. Schwing-Weill and M.A. McKervey in 'Topics in Inclusion Phenomena, Calixarenes, A Versatile Class of Macrocyclic Compounds' eds V. Bohmer and J. V i m . Kluwer Academic Publishers, pp. 149-172, 1990. (3) F. Amaud-Neu. E. M. CoIliins, M. Deasy, G. Ferguson, S.J. Harris, B. Kaitnef, A. J. hugh, M. A. McKervey, E. Marques, B. L. Ruhl, M.J. Schwing-Weill and E. M. Seward, J. Am. Chem. Soc.,1989, 111.8681. (4) D. Diamond, G. Svehla. E. Sewad and M.A. McKervey, Anal. Chim. Acta. ,1988, 204, 223. (5) K. Kimura,T. Miura, M. Matsuo and T. Shono. Anal. Chem.,1990, 62, 1510. (6) D.W.M. Anigan, G. Svehla, S.J. Harris and M.A. McKervey, Electrr;Mnalysk,l994, 6, 97-106. (7) D. Shohat and E. Grushka, Anal. Chem., 1994, 66,747-750. (8)J.H. Park, Y.K. Lee, N.Y. Cheong and M.D. Jang, Chromatographiu, 1993,37(3/4), 221-223. (9) S . Hutchinson, G.A. Kearney, E. Home, B. Lynch, J.D. Glennon, M.A. McKervey and S.J. Harris, Anahtica Chimica Acta, 1994, 291, 269. (10) E. Blasius, K.P. Janzen, W. Klein, H. Kloa, T. Nguyen-Tien, R. Pfeiffer, G. Scholten, H. Simon, H. Stockemer and A. Oouissant, J. ChrOmatogr.,l980, 201, 147166. (1 1) K. Kimura, H. Harino, E. Hayata and T. Shono. Anal. Chem. ,1986,58,2233-2237. (12) J.S. Bradshaw, R.M. Izatt.J.J. christensen, K.E. Krakowiak, B.J. Tarbet, R.L. Bruening and S.Lifson, J. Inclusion Phenomena and Molecular Recognitwn in Chemktry, 1989, 7, 127-136. (13) J. D. Glennon, K. O'Connor. S. Srijaranai, K. Manley, S. J. Harris and M. A. McKervey, Anal. Left., 1993, 26(1), 153. (14) F. Amaud-Neu, M.J. Schwing-Weill, K. Ziat, S. Cremin, S.J. Harris and M.A. McKervey, New J. Chem., 1991, 15, 33-37 (15) H. Small, 'Ion Chromatography' in Modem Analytiical Chemktry Series (D. Hercules, 4 . ) . Plenum Press, New York, 1989.
J. D. Glennon*, B. Lynch, K. Hall, S.J. Hanis and P. O'Sullivan.
DEPARTMENT OF CHEMISTRY.
UNIVERSITY COLLEGE CORK, CORK, IRELAND.
1 ABSTRACT
The retention behaviour of alkali and alkaline earth metal ions on a novel silica bonded macrocyclic calix[4larene tetradiethylamidephase is reported using water-eluent based ion chromatography. Using.a shofl column and water as the mobile phase, the silica bonded phase displays enhanced chromatographicselectivitiesfor Ca2' and S?' over and Ba2' and for Na' over K , Cs' and Li' in line with known complexation selectivity ' from stability constant and extraction data. Selected ternary mixrureS of alkali and alkaline earths can be separated with the elution order Ca2'/Na' >> K ' >' ! g M using water modified with methanol or acetonitde as the mobile phase.
M2'
2 INTRODUCTION
Synthetic macrocyclic compounds known as calixarenes, have the ability, when suitably functionalised. to act as molecular baskets for binding ionic guests. The hostguest interactions of free calix[nlarenes with a variety of neutral and ionic species have been widely reported. While analogies could be drawn with crown ethers or cyclodextxins, the calixarenes are chemically quite unique. Calix[n]arenes are cyclic oligomers composed of phenolic units linked by methylene bridges at positions ortho to the hydmxyl groups. These compounds may contain four to eight aryl moieties arranged in a macrocyclic array with a central cavity.' Derivatisation of the phenolic groups has produced a variety of functionalised calixarenes which show selective ionophoric pmpetties towards selected guest species. The host-guest complexation is determined by the overall macrocyclic structure, most importantly by the cavity size but also by the nature of the functional groups which act as the binding sites. The ionophoric properties of functionalised calixarenes have been clearly demonstrated using NMR spectroscopy and by liquid-liquid extraction studies. Specifically, the conversion of p-ferf-butylcalix[4larene and p-ferf-butylcalix[6lareneinto acetic esters, ketones and amides results in ionophoric activity.2 The phase transfer
154
Progress in Ion Exchange: Advances and Applications
activity of these functionalised calixarenes has been demonstrated for the extraction of metal picrates from water into di~hloromethane.~ Tetrameric calixarene esters, ketones and amides show a selective ability to extract Na+ while the hexameric c a l h n e s have higher efficiencies for Cs+ ions. As with crown ethers, the selective complexation properties of calixarenes have been successfully exploited in the construction of ion selective electrodes4*5and in the development of chemically modified voltammetric sensors.6 However, only recently have applications in chromatography appeared in the literature. Specifically, water soluble calixarenes have been shown to be effective as selectivity modifiers in chromatography and capillary electrophoresis. In particular, the water soluble calix[6]arenepsulphonate has been used in the modification of selectivity for substituted phenols in capillary electrophoresis' and reversed phase liquid chromatography.' Our laboratory has concentrated on the development of novel solid phase materials incorporating functionalised calixarenes, with applications in ion separation and analysis. Solid phase extraction cartridges. incorporating chelating molecular baskets immobilised onto XAD or silica, have been used to sequester metal ions from aqueous s o l ~ t i o n .The ~ quantitative trace enrichment of Cu2+, Zn2+, and Mn2+ from water samples prior to ion chromatographic analysis has been demontrated using immobilised calix[4]arene tetrahydmxamate. The separation of alkali and alkaline earth ions on chemically bonded crown ether stationary phases, using simple water-methanol mobile phases, has previously been r e p ~ r t e d . ~ OThe - ~ ~application of silica bonded calixarene phases in watereluent based ion Chromatography offers exciting possibilities, in view of the established tailoring of selectivity for these ions that is possible through lower rim functionalisation. A silica bonded calix[4]arene tetraester phase has been shown to have e n h a n d chromatographic selectivity for Na+ over other alkali metal ions.l3 In this paper, the use of the silica bonded tetrameric calixarene tetradiethylamide phase for water-eluent based ion chromatographic separation of alkali and alkaline earth metal ions is reported.
3 EXPERIMENTAL Chemicals and reagents.
Silica (Nucleosil, 5pm particle size) was purchased from Macherey-Nagel (Diiren, Germany). HPLC grade methanol and acetonitrile and AnalaR grade toluene were purchased from Merck, (Darmstadt, Germany). All alkali metal salts were AnalaR grade from BDH (Poole. UK). Instrumentation.
For water-eluent based ion chromatography, the system consisted of a Dionex series 4000i metal free pump and injection system, plumbed with PTFE tubing. The injection was pneumatically driven, with a loop volume of 25 pl, unless otherwise stated. The conductivity detector used was a Dionex CDM I1 utilising a Dionex conductivity cell (8 pl volume) and incorporating temperature compensation facilities. Empty stainless steel columns ( 4.5 cm x 4.6 mm i.d.) were slurry packed with the silica bonded calix[4]arene tetraamide phase. An Elgastat water purification system provided water for ion
Ion Chromtography and Electrophoresis
155
chromatography with a resistivity greater than 15Mohm cm. Synthesis of the silica bonded calixI4larene tetradiethylamide phase p-Allylcalix[4]arene was prepared according to the reported procedure' and was converted into its ethyl acetate derivative by refluxing with ethyl bromoacetate in acetone in the presence of anhydrous potassium carbonate as described p r e v i o ~ l y . ~p Allylcalix[4larene tetraacid was treated with oxalyl chloride to afford pallylcalix[4]arene tetraacid chloride, which on treatment with N.Ndiethylamine in tetrahydrofuran was converted to the diethylamide. This pallylcalix[4larene derivative was treated with mercaptopropyl-triethoxysilane at 7OoC for one hour in the presence of cumene hydroperoxide (free radical source for thiolene addition) to yield the triethoxysilane derivative. The silica immobilised caliix[4]arene tetradiethylamide shown in Figure 1, was prepared by refluxing ca. 0.32 g of the triethoxysilyl derivative of the calix[4]arene in 30 ml toluene with 2.0 g of activated Nucleosil for 24 hr. The silica bonded phase was filtered, washed with ca. 100 ml toluene and yielded 6.7% C on elemental analysis. Water-eluent based Ion Chromatography The chromatographic selectivity for alkali metal and alkaline earth metal ions was examined at mom temperature by injection of standard aqueous solutions, prepared in the concentration range from O.lmM - lOmM, onto the calix[rl]arene tetradiethylamide phase with water as the mobile phase. Injections of methanol were used to determine the value. Methanol or acetonitrile in different concentrations was added to the mobile phase and its influence on the retention determined. 4 RESULTS AND DISCUSSION The use of water or other polar solvents as the sole component of the mobile phase in ion chromatography, can eliminate the need for electrolytes, precise mobile phase make-up and ion suppression as part of conductivity detection. This water-eluent based ion chromatography is possible with electrolyte sorbing phases such as ionophoric crown ether phases. While the earliest results with crown ether phases gave broad peaks, excellent alkali metal ion separations were subsequently obtained in a matter of minutes with water as eluent.'0." In the present work, some of the first results obtained with silica bonded molecular baskets, constructed using functionalised calixarenes. are presented. Distinct features of these macrocyclic compounds, apart from their shape, is that very high ion selectivities are possible and that this selectivity can be modulated by suitable functionalisation of the lower rim of the calixarene. In earlier work, with silica bonded tetraethyl calix[4]arene tetraacetate, it has been shown that its Na' selectivity is transferable to silica bonded phases. From extraction and stability constant work, it has been shown that a similar tetrameric calixarene functionalised instead with diethylamide, exhibit, substantial complexation of alkaline earths in addition to Na'. It has the highest reported complexation selectivity for Ca2+ over Mg2+ for a neutral camer ionophore. l4 The structure of this silica bonded calix[4larene diethylamide, prepared from the triethoxysilane derivative, is given in Figure 1. Details of the characterisation of this
156
Progress in Ion Exchange: Advances and Applications
silica bonded phase by solid state NMR are to be presented elsewhere.
-Si-
I 0 --O-~i-O-CH~-CH3 I
Figure 1 Structure of the silica bonded calix[4larene diethylamide phase. In the present work using conductivity detection and with water only as the mobile phase, sodium ions are retained significantly longer than all the other alkali metal ions. While sharp peaks very close to the to are obtained on injections of LiCl, KCl and CsCl, NaCl has a different chromatographic behaviour, is retained and shows fronting. A mivtUre of 5mM NaCl and 5mM KC1 on injection yields close-to-baseliie resolution and a selectivity factor of 5. For alkaline earths, Ca2' and S?' are selectively retained, like Na', while M g ' and Ba2' elute close to to. Again close-to-baselime resolution is obtained on injection of a mixture of Ca2' and M g ' and while the quality of the separation obtained is reduced by broadening of the Ca2' peak, a selectivity factor of 14 is observed. If watedorganic modifier mixtures are utilised instead of pure water as the mobile phase, the retention times obtained for alkali and alkaline earths increase significantlywith the rise of organic fraction in the eluent. These increases are in proportion to the extent of complexation of the ion in the molecular basket. The most noticable feature is how little the retention of ~ g 2 ' varies, staying close to the to. These results are illustrated in Figure 2, where the capacity factors obtained for selected metal ions are plotted against % methanol and % acetonitrile. Acetonitrile is seen to be more effective than methanol at increasing ion retention. In Figure 3, a chromatogram obtained for a mixture of Ca?' and M 8 ' is given to illustrate the type of separation achieved.
157
Ion Chromatography and Electrophoresis
4.5 4
3.5 3
L 2.5 2 1.5 1 0.5 0
0
5
1
0
1
5
2
0
2
5
3
KM
0
5
1
0
1
5
2
0
2
5
0
3
5
4
0
4
0
a
3
0
3
6
K ACN
M2'
Figure 2 Variation of capacity factors for chloride salts of Na+, K+,Ca2+, and as a function of percentage organic modifier in the mobile phase. (concentration: 1mM)
Progress in Ion Exchange: Advances and Applications
158
,
'
.
.
.
L
0 1 2 3 4 5
TIME I MIN
figure 3 Chromatogram obtained on injectionof 5mM CaCl, and 5mM MgCl, on a silica bonded calix[4]arene diethylamide column (20% aqueous MeOH eluent, 1.0 mumin., conductivity detection). A typical chromatogram obtained on injection of a mixture of NaCl, KCl and MgCl, is given in Figure 4, using 20% aqueous acetonitrile.
Mg
K
0
5 10 15
TIME / MIN
Figure 4 Chromatogram obtained on injection of 1mM NaCl, 1mM KCl and 1mM MgCl,. (20% aqueous ACN eluent, 1.0 ml/min., conductivity detection.) 5 CONCLUSIONS Silica bonded calix[4]arene diethylamide stationary phases show selective retention of Na+ , S?+ and Ca2' ions over other alkali and alkaline earth ions injected, with pure
Ion Chromatography and Electrophoresis
159
water mobile phases. These new molecular recognition phases based on macrocyclic calixarenes show enormous potential for the tailoring of chromatographic selectivity thmugh calixarene functionalisation and the use of mobile phase additives. Further work is in progress on these versatile molecular basket sorbent phases for ion Separation and analysis.
ACKNOWLEDGEMENTS The authors wish to gratefully acknowledge the help and advice given by Professor M.A. McKervey, School of Chemistry, Queens University, Belfast. Thanks also to Ms. G. Flynn for work in the laboratory.
(1) C.D. Gutsche, 'Calixarenes', Vol 1 inMonographs in Supramolecular Chemktry, ed. J.F. Stoddart, Royal Society of Chemistry. 1989. (2) M.J. Schwing-Weill and M.A. McKervey in 'Topics in Inclusion Phenomena, Calixarenes, A Versatile Class of Macrocyclic Compounds' eds V. Bohmer and J. V i m . Kluwer Academic Publishers, pp. 149-172, 1990. (3) F. Amaud-Neu. E. M. CoIliins, M. Deasy, G. Ferguson, S.J. Harris, B. Kaitnef, A. J. hugh, M. A. McKervey, E. Marques, B. L. Ruhl, M.J. Schwing-Weill and E. M. Seward, J. Am. Chem. Soc.,1989, 111.8681. (4) D. Diamond, G. Svehla. E. Sewad and M.A. McKervey, Anal. Chim. Acta. ,1988, 204, 223. (5) K. Kimura,T. Miura, M. Matsuo and T. Shono. Anal. Chem.,1990, 62, 1510. (6) D.W.M. Anigan, G. Svehla, S.J. Harris and M.A. McKervey, Electrr;Mnalysk,l994, 6, 97-106. (7) D. Shohat and E. Grushka, Anal. Chem., 1994, 66,747-750. (8)J.H. Park, Y.K. Lee, N.Y. Cheong and M.D. Jang, Chromatographiu, 1993,37(3/4), 221-223. (9) S . Hutchinson, G.A. Kearney, E. Home, B. Lynch, J.D. Glennon, M.A. McKervey and S.J. Harris, Anahtica Chimica Acta, 1994, 291, 269. (10) E. Blasius, K.P. Janzen, W. Klein, H. Kloa, T. Nguyen-Tien, R. Pfeiffer, G. Scholten, H. Simon, H. Stockemer and A. Oouissant, J. ChrOmatogr.,l980, 201, 147166. (1 1) K. Kimura, H. Harino, E. Hayata and T. Shono. Anal. Chem. ,1986,58,2233-2237. (12) J.S. Bradshaw, R.M. Izatt.J.J. christensen, K.E. Krakowiak, B.J. Tarbet, R.L. Bruening and S.Lifson, J. Inclusion Phenomena and Molecular Recognitwn in Chemktry, 1989, 7, 127-136. (13) J. D. Glennon, K. O'Connor. S. Srijaranai, K. Manley, S. J. Harris and M. A. McKervey, Anal. Left., 1993, 26(1), 153. (14) F. Amaud-Neu, M.J. Schwing-Weill, K. Ziat, S. Cremin, S.J. Harris and M.A. McKervey, New J. Chem., 1991, 15, 33-37 (15) H. Small, 'Ion Chromatography' in Modem Analytiical Chemktry Series (D. Hercules, 4 . ) . Plenum Press, New York, 1989.