Anal.
(5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16)
Chem. 1987, 5 9 , 2241-2245
Hare, P. E.; Gil-Av, D. Science 1979, 204, 1226-1228. Guiochon, G.; Colin, H. Chromafogr. Forum 1988, 7 , 21-28. Lonsdale, H. K. J. Membr. Scl. 1982, 10, 81-181. Reusch, C. F.; Cussler, E. L. Am. Inst. Chem. Eng. J. 1973, 19, 736-746. Wong, K. H.; Yagi, K.; Smid, J. J. Membr. B o / . 1974, 18, 379-397. Cussler, E. L.; Evans, D.F. J. Membr. Sci. 1980, 6,113-121. Christensen, J. J.; Lamb, J. D.; Izatt, S. R.; Starr, S. E.; Weed, G. C.; Astin. M. S.;Stitt, 9. D.; Izatt, R. M. J . Am. Chem. SOC. 1978, 100. 3219-3220. Lamb, J. D.;Christensen, J. J.; Oscarson, J. L.; Nielsen, 9. L.; Asay, B. W.; Izatt, R. M. J. Am. Chem. SOC.1980, 102. 6820-6824. Izatt, R. M.; Dearden, D. V.; Brown, P. R.; Bradshaw. J. S.; Lamb, J. D.; Christensen, J. J. J. Am. Chern. SOC. 1983, 105, 1785-1790. Charewlcz, W. A,; Bartsch, R. A. J. Membr. Sci. 1983, 12, 323-333. Oi, 2.: Cussler, E. L. J. Membr. S d . 1984, 19, 259-272. Newcomb, M.; Toner, J. L.; Helgeson, R. C.; Cram, D. J. J. Am. Chem. SOC.1979, 101, 4941-4947.
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(17) Yamaguchi, T.; Nishimura, K.; Shinbo, T.; Sugiura, M. Chem. Lett. 1985, 1549-1552. (18) Armstrong, D. W.; Ward, T. J.; Czech, A.; Czech, B. P.; Bartsch, R. A. J. Org. Chem. 1985, 50, 5556-5559. (19) Armstrong, D. W.; DeMond, W.; Czech, 9. P. Anal. Chem. 1985, 5 7 , 481-484. (20) Armstrong, D. W.; DeMond, W.; Aiak, A,; Hinze, W. L.; Riehl, T. E.; Bui, K. H. Anal. Chem. 1985, 5 7 , 234-237. (21) Armstrong, D. W.; Ward, T.J.; Armstrong, R. D.;Beesley, T. E. Science 1986, 232, 1132-1135.
RECEIVED for review March 5, 1987. Accepted June 11, 1987. Support of this work by the National Institute of General Medical Sciences (BMT 1 ROI GM 36292-01) is gratefully acknowledged.
Effect of (Ethylenediaminetetraacetato)copper(II)and Bis(ethylenediamine)copper(I I)Eluents on Nonsuppressed Ion Chromatography with Indirect Photometric Detection Kazuichi Hayakawa,* Takehiko Sawada, Kazue Shimbo, and Motoichi Miyazaki
Faculty of Pharmaceutical Sciences, Kanazawa Uniuersity, 13-1, Takara-machi, Kanazawa, 920 J a p a n
Two copper( I I ) chelates, disodium (ethylenedlaminetetraacetato)copper( I I ) , Na,[Cu(edta)], and bis(ethylened1amlne)copper( I I ) sulfate, [Cu(en),]SO,, were used as eluents In nonsuppressed Ion chromatography wlth lndlrect photometric detectlon. NaJCu(edta)] eluent was able to separately determine lnorganlc and carboxyilc anions on an anion exchange column. The eluent has a slightly lower anion exchange ablllty and a broader ultraviolet absorption avallabie for detectlon than the disodium phthalate eluent which has been commonly used. Wlth addltlon of excess Na,H,edta to the NaJCu(edta)] eluent, not only anions but ako metal ions were determined as metal-edta anion chelates. [Cu( en),]SO, eluent was able to separately determlne lnorganlc catlons on a catlon exchange column. This eluent has a significantly stronger cation exchange ablllty and a broader (ultraviolet and vlslble) absorption than the CuSO, eluent that has been commonly used. The detection llmlts for both anions and cations under the condltlons described above are below 10-ng levels of injected analytes.
Indirect photometric chromatography (IPC) (1) based on the difference of absorbances of sample and eluent ions (2) has attracted much attention in the recent development of ion chromatography (IC). IPC extends the application of IC to any high-performance liquid chromatography (HPLC) system capable of ultraviolet (UV) absorbance detection. The optimization of IPC conditions and applications of the technique have been reported (3-14). The authors have also reported the determination of inorganic cations and anions by similar approaches (15, 16). The choice of eluent for IPC has been limited to several species having large UV absorptions and ion exchange abilities. In the reports cited above, aromatic carboxylate solutions such as phthalate and trimesate have been mainly used as eluents for the determination of anions. On the other hand, copper(I1)
solution such as CuS04 and Cu(NOJ2 have been the main eluents used for inorganic cations. When only these eluents are used, there are some problems with IPC. For example, (1) simultaneous determination of both anions and cations is difficult, (2) a visible absorbance detector is not available, and (3) a column of low ion exchange capacity is necessary. These characteristics have restricted the use of IPC. From these facts, the authors have investigated metal complexes as eluents for IPC and have found some useful ionic metal complexes. There has been only one report on the use of a metal-complex eluent in IPC. Iron(I1) 1,lOphenanthroline was used as an ion interaction reagent for the determination of inorganic anions on a reversed-phase column (17).
In this paper the authors describe the properties and the effective use of disodium (ethy1enediaminetetraacetato)copper(II), Naz[Cu(edta)],and bis(ethylenediamine)copper(II) sulfate, [ C ~ ( e n ) ~ ] as S 0eluents ~ for ion exchange columns in nonsuppressed IC with indirect photometric detection. EXPERIMENTAL SECTION Apparatus. HPLC used in the experiments consisted of the following apparatus: a Shimadzu LC-6A pump with a Rheodyne 7120 sample injector, a Shimadzu CTO-2A column oven, a Shimadzu SPD-6AV variable-wavelength UV-visible absorbance detector, and a Nippon Denshi U-125 recorder. The polarity of the recorder was reversed. An anion separating column (150 X 3.0 mm id., stainless) was packed with Mitsubishi Chemical MCI SCA-01 (polyacrylatebased, anion exchange capacity 0.01 mequiv/g, particle size 20 pm). A cation separating column (250 X 4.6 mm id., stainless), was packed with Mitsubishi Chemical MCI CPK-08 (styrenedivinylbenzene copolymer, cation exchange capacity 1.7 mequiv/g, particle size 20 pm). HPLC Conditions. Typical conditions for inorganic and M Na2[Cucarboxylic anions were as follows: eluent, 1.5 X (edta)];flow rate, 0.5 mL/min; column temperature, 40 "C; detection wavelength, 325 nm (0.02 AUFS); injection volume, 50 pL. Typical conditions for simultaneous determination of both anions and metal ions were as follows: eluent, 5.0 X loT4M
0003-2700/87/0359-2241$01.50/0 0 1987 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 59, NO. 18, SEPTEMBER 15, 1987
Table I. Capacity Factors (k')of Anions with Na2[Cu(edta)]Eluent"
analyte
c1-
NO,BrNOC SO?-
acetate lactate propionate acrylate pyruvate
k'
analyte
k'
0.94 1.25 2.69 3.06 6.75 0.38 0.38 0.56 0.63 0.69
n-butyrate succinate malonate L-malate DL-tartrate oxalate [Fe(edta)][Mg(edta)],[ Zn (edta)]
1.13 2.25 2.81 3.38 4.56 8.50 0.63* 3.19 5.88
uColumn,MCI SCA-01 (150 X 3.0 mm id.); eluent, 1.5 X Nao,lCu(edta)l:temDerature. 40 "C. *Positive peak. ~~~~~~
~
I
I
0.002 AU
0
M
~
Naz[Cu(edta)]to 5.0 x M Na,H,edta; detection wavelength, 290 nm (0.04 AUFS); injection volume, 20 pL. The other conditions were the same as those described above. Typical conditions for inorganic cations were as follows: eluent, 1.0 X M [Cu(en),]SO,; flow rate, 1.0 mL/min; column temperature, 30 "C; detection wavelength, 295 nm and 550 nm (0.02 AUFS); injection volume, 20 p L . Reagents and Solutions. Na,[Cu(edta) 1, CuS04,Na,H,edta, ethylenediamine (en) and disodium phthalate (Na2Ph) were purchased from Wako Pure Chemicals (Tokyo, Japan). All other chemicals used were of analytical reagent grade. [ Cu(en),]S04 solution was prepared by dissolving CuSO, and en in water at the molar ratio of 1:2. The other eluent solutions, Na,[Cu(edta)J, CuS04,NazH2edta,and NazPh were prepared by dissolving the appropriate amounts of crystals in water. The eluent pH was adjusted to 6.5 iz 0.1, if necessary, with HzS04or NaOH. All eluents were filtered with a Fuji Film membrane filter FR-40 (pore size 0.4 pm) before use. Anion sample solutions were prepared by dissolving sodium salts of the corresponding anions in water. Cation sample solutions were prepared by dissolving the corresponding chlorides in water. Stability and Dissociation Constants. All constants in this report were cited from ref 25.
RESULTS AND DISCUSSION Naz[Cu(edta)]. As metal-edta complexes, both Cu(edta) and Fe(edta) have large UV absorptions. As these complexes contain unchelated carboxylic acid groups they are anions in a solution of neutral pH. Cu(edta) was found to be a stronger anion exchange eluent than Fe(edta). This is not surprising as the former has two free carboxyl groups while the latter has only one free carboxyl group. Therefore, this report deals mainly with Cu(edta). With 1.5 x M Na2[Cu(edta)],pH 6.5, used as an eluent, inorganic and carboxylic anions were separately eluted (Table I). Column temperature was controlled at 40 "C to give reproducible separations, since the capacity factors of anions changed with the variations of the temperature. A typical chromatogram of inorganic anions is shown in Figure 1. Non-UV-absorbing sample ions appear as "negative peaks", which are the decreases in base line absorbance of the eluent, so that chromatograms in this report are given as typical appearances by reversing the recorder polarities. The ratio of signal to base line random noise level (S/N) was largest a t 325 nm, although the peaks could be detected even at 350 nm. When NasPh eluent was used the peaks could not be detected
10 15 Time (min)
5
0
20
Figure 1. Separation of five inorganic anions with Na,[Cu(ectta)] eluent: (1) CI-, 0.79 pg; (2) NO,-, 1.2 pg; (3) Br-, 2.0 pg; (4) NO
