2464
Anal. Chem. 1988, 60,2464-2467
ArH ArH'Ar'
+ le-
s ArH'-
E30 = -2.10 V
K2 + ArCl z== ArH + ArC1'K 2 = 750 + ArH rAr- + ArH'- K3 > 1 X lo5 K3
The values for the equilibrium constants (K2,K3) were estimated from the relevant Eo values. The simulated voltammogram for this case, incorporating the effect of ohmic drop, is in good agreement, further supporting the assigned mechanism. The uncertainty in the additional parameters affecting the second wave leads to a corresponding uncertainty in the fit of this process. However, the rate constant for the decomposition of the radical anion fits well with both of the simulations and is comparable to that measured by redox catalysis (26).
LITERATURE CITED (1) Howell, J. 0.; Wightman, R. M. Anal. Chem. 1984, 5 6 , 524-529. (2) Howell, J. 0.;Wightman, R. M. J. Phys. Chem. 1984, 8 8 , 39 15-39 18. (3) Montenegro, M. I.; Pletcher, D. J. Electroanal. Chem. 1988, 200, 371-374. (4) Fitch, A.; Evans, D. H., J. Electroanal. Chem. 1988, 202, 83-92. (5) Amatore, C. A.; Jutland, A.; Pfluger, F. J. Electroanal. Chem. 1987, 218, 361-365. (8) Wehrneyer, K. R.; Wightman, R. M. Anal. Chem. 1985, 57, 1989- 1993. (7) Howell, J. 0.; Goncalves, J.; Amatore, C.; Klaslnc, L.; Wightman, R. M.; Kochi, J. K. J. Am. Chem. SOC.1984, 106, 3968-3976. (6)Andrieux, C. P.; Garreau, D.; Hapiot, P.;Pinson, J.; Saveant, J. M. J. Electroanal. Chem. 1988, 243,321-335. Kristensen, E. W.; Deakin, M. R. Anal. Chem. 1988, 6 0 , (9) Wipf, D. 0.; 308-3 IO. (10) Schwall. R. J.; Bond. A. M.; Smith, D. E. Anal. Chem. 1977. 49, 1805-1812. (11) Suprenant, H. L.; Ridgway, T. M.; Reilley, C. N. J. Electroanal. Chem. 1977, 75, 125-134.
(12) Smith, D. E. Anal. Chem. 1978, 48, 517A-526A. (13) Deutscher, R. L.; Fletcher, S. J. Electroanal. Chem. 1988, 239, 17-54. (14) Hawley, M. D. Encyclopedia of Electrochemistry of the Elements; Bard, A. J., Lund, H., Eds.; Dekker: New York, 1980; Vol. XIV, Chapter 1. 15) Wightman, R. M.; Wipf, D. 0. Electroanalytical Chemistry: Bard, A. J., Ed.; Dekker: New York, in press. 16) Sawyer, D. T.; Roberts, J. L. Experimentalflechochemistry for Chemists; Wiley: New York, 1974. Kuhr, W. G.; Ensman, R. E.; Wightman, R. M. J. flec17) Howell, J. 0.; troanal. Chem. 1988, 209, 77-90. 16) Bond, A. M.; Fieischmann, M.: Robinson, J. J. Electroanal. Chem. 1984, 168, 299-312. (19) Engstrom, R. C.; Wightman, R. M.; Kristensen, E. W. Anal. Chem. 1988, 6 0 , 652-656. (20) Horiick, G.;Hieftje, G. M. Correlation Methods in Chemical Data Mea surement; Plenum: New York, 1978; pp 153-216. (21) Bard, A. J.; Faulkner, L. R. Electrochemical Methods; Wiley: New York, 1980. (22) Feldberg, S.W. Electroanalytical Chemistry; Bard, A. J., Ed.; Dekker: New York, 1969; Vol. 3. (23) Imbeaux, J. C.; Saveant, J. M. J. Electroanal. Chem. 1970, 28, 325-338. (24) Fratoni, S. S.,Jr.; Perone, S. P. Anal. Chem. 1976, 48, 287-295. (25) Miaw, L. L.; Perone, S.P. Anal. Chem. 1979, 51, 1645-1650. (26) Anderson, J. L. Chem. Insfrum. 1978, 7,25-32. (27) Garreau, D.; Saveant, J. M. J. Electroanal. Chem. 1974, 5 0 , 1-22. (28) Saveant, J. M.; Tessier, D. J. Elechoanal. Chem. 1977, 77, 225-235. (29) Andrieux, C. P.; Blocman, C.; Dumas-Bouchat, J. M.; M'Haila, F.; Saveant, J. M. J. Am. Chem. SOC.1980, 102, 3806-3813. (30) Amatore, C.; Saveant, J. M. J. Electroanal. Chem. 1977, 85, 27-46. (31) Arnatore, C.; Saveant, J. M. J. Electroanal. Chem. 1978, 8 6 , 227-232. (32) Nicholson, R. S. Anal. Chem. 1985, 37, 1351-1355. (33) Kojima, H.;Bard, A. J. J. Am. Chem. SOC.1975, 97, 6317-6324. (34) Wayner, D. D. M.: McPhee. D. J.; Griller, D. J. Am. Chem. SOC. 1988, 110, 132-137.
RECEIVED for review May 9, 1988. Accepted August 2, 1988. This work was supported by the National Science Foundation (CHE-8500529). D.O.W. is the recipient of a Monsanto Fellowship.
Copper(I I)-Selective Electrode Using Thiuram Disulfide Neutral Carriers Satsuo Kamata,* Ajay Bhale, Yumi Fukunaga, and Hiroyuki Murata Faculty of Engineering, Kagoshima University, Korimoto, Kagoshima 890, J a p a n
Poly(vinyl chloride)-membrane electrodes that are hlghly selective and sensttlve to Cu( I I ) Ions were developed by using neutral carriers such as tetraethyl-, tetrabutyl-, and dlmethyldloctadecylthluram dtsulflde and o-nltrophenyloctyl ether as a plastlclrlngsolvent mediator. The electrodes exhibit a Nemstian slope of 30-31 mV per concentration decade at 25 'C. These compounds form an almost 1:l catfon/lonophore ligand complex for uptake of Cu( I I ) ion. Properties of the electrodes are discussed.
Ion-selective electrodes based on neutral carrier ligands are well established for alkali metal and alkaline-earth metal cations (1-6). Essentially, the neutral carriers have the characteristics of being uncharged, lipophilic, and undergoing reversible complexation with selected cations and hence of promoting cation transfer between the aqueous phase and the organic membrane phase by means of carrier translocation.
The selection of suitable neutral carriers for ion sensing can be helped by structural studies on the interaction between carriers and ions. In this respect, macrocyclic and nonmacrocyclic compounds have attracted wide spread attention due to the unique properties of these types of compounds (7-1 1). Macrocyclic ligands have the ability to discriminate among closely related metal ions based on the relative fit of the ligand cavity size to the metal ion radius (ring size effect) (12-20). Both the ring size and macrocyclic effects have been extensively examined from a thermodynamic standpoint (21-23). Recently, much interest has been focused on nonmacrocyclic compounds (24). These compounds form selective and ideal complexes with the calcium cation and were successfully used as a neutral carrier in the ion-selective electrode (25). It is also well-known that dithiocarbamate derivatives are highly versatile chelating agents for metal cations, but these compounds form complexes with many metals as nonselective complexing agents (26). Considering this remarkable ability
0003-2700/88/0360-2464$01.50/00 1988 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 60, NO. 22, NOVEMBER 15, 1988
2465
Table I. Membrane Composition of Ion-Selective Electrodesn S
C2Hg
I
S
\$
S
R1
CqHg
: 1
I
electrode
TETDS
: 2, TBTDS
1
2
3
component
TETDS
TBTDS
DMDOTDS
ionophore
4.1 54.8 41.1
5.4 54.1 40.5
5.4 54.1 40.5
NPOE
I
/ N\
CqH9
C2H5
CH3
C18H37
: 3 , DMDOTDS
R2
PVC
Values are mass ratio in percent.
Flgure 1. Constitution of thiuram disulfides employed as a neutral
carrier for Cu(I1)-selective electrode of dithiocarbamates and nonmacrocyclic type compounds, recently we prepared o-xylylenebis(dithiocarbamate) and successfully used it as a neutral carrier in a Cu(I1)-selective membrane electrode (11). This type of compound forms selective complexes with metal cations due t o their flexible structure, appropriate position of two dithiocarbamate radicals, and their nonmacrocyclic cavities with four donor sulfur atoms. Thus, a further improvement of the selectivity of Cu(I1)-selective electrodes should be feasible. In this paper, we report on a sensing system involving tetraethylthiuram disulfide (TETDS), tetrabutylthiuram disulfide (TBTDS), and dimethyldioctadecylthiuramdisulfide (DMDOTDS) with o-nitrophenyloctyl ether (NPOE) as a plasticizing solvent mediator. These new sensor materials each having a C-shaped cavity with donor sulfur atoms were expected to form selective complexes with transition-metal cations and to give an improved detection limit for the Cu(1I) ion.
EXPERIMENTAL SECTION Reagents. TETDS and TBTDS were obtained from Tokyo Kasei Kogyo, Japan. DMDOTDS was prepared by the procedure described in this section. Solvents were used without further purification unless stated otherwise. A list of other reagents and suppliers follows: Poly(viny1chloride) (PVC) and NPOE (Fluka, Switzerland); metal chloride of copper, zinc, cobalt, nickel, lead, manganese, magnesium, calcium, strontium, sodium, and potassium were obtained from Kanto Kagaku, Japan. All solutions were prepared with distilled, deionized water from analytical reagent grade materials. All other materials and chemicals were of the best available laboratory reagent grade. Preparation of DMDOTDS. Sodium N,"-methyloctadecyldithiocarbamate was prepared by the following procedure. Methyloctadecylamine (0.03 M) and sodium hydroxide (0.03 M) were dissolved in a 1:l aqueous ethanolic solution (200 mL). This mixture was stirred a t room temperature and carbon disulfide (2.73 mL) was slowly added. The resultant precipitate of sodium N,N'-methyloctadecyldithiocarbamate was obtained after the evaporation of ethanol. The compound was crystallized with distilled ethanol, yield 52%. DMDOTDS was prepared by the oxidation of the sodium A',"-methyloctadecyldithiocarbamate (0.01M) with a hydrogen peroxide (0.57 mL) and sulfuric acid (0.51 mL) mixture in a 1:6 aqueous ethanolic solution (350 mL). The mixture was stirred for 2 h at room temperature. The final compound was obtained by crystallization with an ethanolchloroform (101)mixture: yield 43%, mp 74-76 "C. Anal. Calcd H, 11.24; C, 66.98; N, 3.91. Found: H, 11.46; C, 67.28; N, 3.95. The purity of DMDODTS was also checked by HPLC (LC-6A, Shimadzu Co. Japan) on an octadecylsilanemodified silica column (Shim-Pack CLC-ODS(M)) and a single peak with a retention time of 1.96 min was obtained. PVC Membrane Fabrication. The method for preparing PVC immobilized neutral carrier membrane is as reported previously (7). Ionophore, NPOE, and PVC were dissolved in 5 mL of tetrahydrofuran (THF). The THF solution was poured into a glass ring of 35 mm diameter on a glass plate and kept for 24 h at 30 "C. A membrane disk of 6 mm diameter was cut with a master membrane and was fixed to the PVC tubing. The electrodes were conditioned before use by immersion for 24 h in
/
h0-0' 9
8
-
0 7
6
5
4
3
2
1
log [ ( aCu2+)/M 1
Flgure 2. Electrode responses for Cu(I1) ion, the Cu(I1)-selective membrane electrode based on ionophores (1)TETDS, (2) TBTDS, and (3) DMDOTDS, respectively.
M CuClz solution. The membrane composition for Cu(I1) ion is summarized in Table I. Electrode System and emf Measurements. A cell assembly of the following type was used. Ag-AgC1J10-3 M CuCl,(sensor membraneisample solutionlreference electrode. All the emf observations were made relative to a saturated calomel electrode (Iwaki Glass, Japan) with a Corning Digital 112 research pH meter. The performance of the electrodes was investigated by measuring the emfs of copper chloride solutions prepared with a concentration range of 10-1-10-9 M by serial dilution. Each solution was stirred and the potential reading was recorded when it became stable, and then plotted as a logarithmic function of Cu(I1) cation activity. The activities of metal ions were based on the activity coefficient y, data calculated from the modified form of the Debye-Huckel equation, which is applicable to any ion log y = - 0 . 5 1 1 ~ ~ [ w ~ /-I~ /1.5p1/') (1 - 0.2~1
(1)
where is the ionic strength and z the valency. All measurements were carried out at 25 f 0.1 "C, using a Coolnit BCL19 thermostat (Taiyo Kagaku Kogyo, Japan). All the metal chloride solutions were freshly prepared by accurate dilution from their stock standard solution of 0.1 M, with distilled, deionized water. The concentration of solutions was checked by an atomic absorption spectrophotometer Model SAS-727 (Daini Seikosha, Japan).
RESULTS AND DISCUSSION The response characteristics of the three electrodes are shown in Figure 2. The electrodes based on TETDS and
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ANALYTICAL CHEMISTRY, VOL. 60, NO. 22, NOVEMBER 15, 1988
-2
t
-3
-
-4
-
-5
-
-l
t
2
3
4
5
6
7
-
PH
Flgure 3. Effective pH range for Cu(I1) ion, the Cu(I1)-selective
electrode cell assembly based on ionophores (1) TETDS, (2) TBTDS. and (3) DMDOTDS, respectively.
2 -
Table 11. Properties of Cu(I1)-Selective Membrane Electrodes"
Figure 4. Selectivity characteristics for Cu(I1)ion, incorporating different metal cations, the electrode construction based on ionophores is as follows: (1) TETDS, (2) TBTDS, and (3) DMDOTDS.
electrode property ionophore detection limit, M slope, mV/decade response time: s pH rangec
1
2
3
TETDS
TBTDS
DMDOTDS
2.0 X 30 27 3.2-5.4
1.0 X 31 10 3.0-6.5
4.0 X 31 6 3.7-6.3
3 -
" Reproducibility of the electrodes checked three times and the mean values shown. *Measuredby 10-fold increase in Cu(I1) ion concentration Le., to M. Measured in M CuC12 solution. ~~
TBTDS ionophores gave better Nernstian linearity with straight lines from 10-' to M and lo-* M, respectively. But highly lipophilic DMDOTDS, although it has the same C-shaped cavity with donor sulfur atoms, gave a linearity of M. This indicates that the complex formation ability of DMDOTDS is inadequate probably due to the steric hindrance of the long-chained alkyl groups. The pH response profile for electrodes was examined by use of M CuC12 solutions. The pH was adjusted by introducing small drops of hydrochloric acid (0.1 M) or sodium hydroxide (0.1 M). The influence of the pH response on the PVC membrane electrodes is shown in Figure 3. Generally, it was observed that above p H 6, the potential of membrane electrodes decreased due to the formation of copper hydroxide in solution. This drop in the potential is also dependent on the resistance of the electrode membrane with ionophore in alkali media. The potential for the membrane with TETDS dropped at pH 5.4 rather than pH 6. This indicates the weak resistance of the TETDS ionophore in alkali media. On the other hand, the increasing potential a t low pH means that the electrodes respond to hydrogen ions. The response time of the electrode was tested by measuring the time required to achieve a steady potential within 1mV M solution by a rapid 10-fold fluctuation for a to increase in the Cu(I1) ion concentration. The response time of the electrodes based on the neutral carriers TETDS, TBTDS, and DMDOTDS yielded a steady potential within 27, 10, and 6 s, respectively. The properties of electrodes are summarized in Table 11.
Potentiometric selectivity coefficient (K&J values were determined by using the mixed solution method (8). The interference of mono- and divalent cations was evaluated by mingling the equivalent volume of lo-' and lo-, M of respective metal chlorides, except for PbC12 (10-3M) in CuC1, solutions, i.e., lo-' to lom9M. The selectivity coefficient for the electrodes is summarized in Figure 4. The membrane based on ionophore TETDS or TBTDS showed better selectivity factors for the different metal cations than electrode 3 based on DMDOTDS. Membrane electrode 1 rejected alkali and divalent metal cations by a factor in the range of 103-104, except for Pb(II), while in the case of electrode 2, the divalent interference was predominant over the monovalent cations. Membrane 3 showed interference from alkali, Pb(II), and Zn(I1) cations. The above results clearly demonstrate that membrane electrode 1 has shown the best selectivity for Cu(I1) ion except for Pb(I1) interference. The sensitivity and selectivity can be improved by the addition of a small amount of lipophilic anion excluder to the membrane. TETDS, TBTDS, and DMDOTDS, which have C-shaped cavities with four donor sulfur atoms, tend to form a 1:l Cu2+/ionophore complex. The 1:l complex formation ability of these compounds was observed by the solvent extraction method. The extraction experiment was carried out in dichloroethane using Cu2+ion and TETDS ligand. A graph was plotted showing the relationship between the distribution ratio and the ligand concentration, log D vs log [L](,,, forming a straight line with a slope of one. The extraction was expressed in the following equations: cu2+
+ 2 x - + L(,) = CUX,L(,)
K , = [ c ~ x , L l ( o ) / [ c ~ 2[X-l2[L1(o) +l D = [CuX,L](,)/ [CU"]
(2)
(3) (4)
where X is an anion and K,, is the extraction coefficient, and ( 0 ) refers to the species in the organic phase. When we sub-
Anal. Chern. 1988, 60, 2467-2472
stituted (4)for (3), the following equations were obtained:
D = ~ex[X-l2[LI(o) log D = log
KeX[X-l2 + log [L](,)
(5)
(6)
This therefore confirms the 1:1complex formation ability of ionophore for Cu(I1) ion. T E T D S ligand has a n almost ideal C-shaped nonmacrocyclic cavity to fit the Cu(I1) ion. But DMDOTDS did not form an ideal coordination complex sphere for Cu(I1) ion compared to TETDS, and hence the sensitivity and selectivity are not so good. On the other hand, TBTDS was observed to have a different behavior in regard to the selectivity of foreign ions. These differences in selectivity are probably due to the steric hindrance of the n-butyl chain which affects the cavity Of the compound* It was confirmed that the selectivity of TBTDS tended to become similar to that of the other two(TETDS,DMDOTDS), with the addition of a bulky alkyl group such as isobutyl chain, On the basis of above results, it is considered that an alkyl chain also plays an important role in sustaining the C-shaped cavity of the compound.
CONCLUSION The results presented here clearly demonstrate that high selectivities may be induced with nonmacrocyclic ligands, as Dredicted earlier (25,27). The nonmacrocyclic neutral carriers i r e quite versatile as chelating agents, somewhat superior to the macrocyclic ligand. TETDS has shown better Sensitivity and selectivity than TBTDS and DMDOTDS for Cu(I1) ion. These neutral carriers have almostideal C+haped cavities to fit Cu(I1) ion, and form a 1:l cation/ionophore coordination sphere. Also the alkyl chain Plays an important role in Nutaining the C-shaped cavities for the formations of metal complexes. A highly selective electrode opens several new aspects in Cu(I1) ion analysis.
ACKNOWLEDGMENT The authors gratefully acknowledge Professor W. Simon of the Swiss Federal Institute of Technology (ETH) for helpful
2407
discussion and encouragement.
LITERATURE CITED (1) Oehme, M.; Simon, W. Anal. Chlm. Acta 1978, 86, 21. (2) Meier, P. C.; Morf, W. E.; Laubli, M., Simon, W. Anal. Chim. Acta 1984. 156, 1. (3) Simon, W.; Pretsch, E.; Morf, W. E.; Ammann, D.; Oesch, U.; Dinten, 0. Analyst (London) 1984, 109, 207. (4) Kimura, K.; Ishlkawa. A.; Tamura, H.; Shono, T. J . Chem. Soc., Perkin Trans. 1984, 2 , 447. (5) Nieman, T. A.; Horvai, G. Anal. Chim. Acta 1985, 170, 359. (6) Kitazawa, s.; Kimura, K.; Yano, H.; Shono, T. Analyst (London) 1985, 110, 295. (7) Karnata, S.; Higo, M.; Kamibeppu, T.; Tanaka, I . Chem. Lett. 1982, 287. ( 8 ) Kamata, S . ; Yamasaki, K.; Higo, M.; Bhale, A,; Fukunaga, Y. Analyst (London) 1988, 113, 45. (9) Morf, W. E.; Ammann, D.; Simon, W. Chimia 1974, 28. (10) Morf, W. E.; Kahr, G.; Simon, W. Anal. Lett. 1974, 7 , 9. (12) (11) Frensdorff, Kamata, S.;H,Ogawa, K, J , Am, F.; Fukumoto, Chem, sot. M. Chem. 1971, 93, Lett. 6oo, 1987, 533. (13) Pedersen, C. J.; Frensdorff, H. K. Angew. Chem., Inf. Ed. Engl, 1972, 1 1 , 16. (14) Christensen, J. J.; Hill, J. 0.; Izatt, R. M. Science (Washington, D.C.) 1971, 774, 459. (15) Izatt. R. M.; Eatough D. J.; Christensen, J. J. Struct. Bonding (Berlin) 1973. 16, 161. (16) Christensen, J. J.; Eatough D. J.; Izatt, R. M. Chem. Rev. 1974, 7 4 , 351. (17) Busch, D. H.; Farmery, K.; Goedken, V.; Katovlc, V.; Melnyk, A. C.; Sperate, C. R.; Tokel, N. A&. Chem. Ser. 1971, No. 100, 52. (18) Martin, L. Y.; DeHayes, L. J.; Zornpa, L. J.; Busch, D. H. J . Am. Chem. SOC. 1974, 96, 4046. (19) Watkins, Jr., D. D.; Reley, D. P.; Stone, J. A,; Busch, D. H. Inorg. Chem. 1976, 15, 387. ~ ~, ~ ~s, c, k s,~c,; l it,~ A, ,M,; ~ ~ D. H.~ (20) H ~ y,; ~~ ~ ~r tL,,i y,; J. Am. Chem. SOC. 1977. 99. 4029. (21) Hinz. F. P.; Margerum. D. W. Am. Chem. SOC. 1974, 96, 4993. (22) Hinz, F. P.; Margerum, D. W. Inorg. Chem. 1974, 13, 2941. (23) Smith, G. F.; Margerum, D. W. J . Chem. Soc ., Chem. Commun. 1975, 807. (24) Prestsch, E.; Ammann, D.; Osswald, H. F.; Guggl, M.: Simon, W. Helv. Chim. Acta 1980, 63, 191. (25) Schefer, U.; Ammann, D.; Pretsch, E.; Oesch, U.; Simon, W. Anal. Chem 1988 58 2282 (26) Thorn,'G, D,; Lud;uig,R: A. The Dithiocarbamates and Related Compounds; Elsevler: Amsterdam and New York, 1962; Chapter 6. (27) Simon, W.; Morf, W. E.; Meier, P. C. Struct. Bonding (Berlin) 1973, 16, 113.
i.
RECEIVED for review March 10, 1988. Resubmitted August 9,1988. Accepted August 9,1988. This work was supported by the Japanese Ministry of Education, Science and Culture.
Role of Monomer in y-Irradiated Dimethyldiallylammonium Chloride Modified Electrodes Edward W. Huber and William R. Heineman* Edison Sensor Technology Center, Biomedical Chemistry Research Center, and Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221-01 72 Commerclally available poly( dlmethyldlallylammonlumchloride) (pdyDMDAAC) solutlons were found by NMR to contain DMDAAC monomer. Polymerization of this monomer by y lrradiatlon results In the formation of Insoluble networks that can be Lmmobilzed on electrode surfaces. The lmmoblllzatlon process Is aided by the high porosity of the graphite electrodes used. The permeablllty of these polyDMDAAC electrodes to solution species can be controlled by varying the amount of monomer polymerlzed. The feasibility of ImmobC llzlng macromolecules onto electrode surfaces by polymerization of monomers Is studied by lmmobllizlng polyDMDAAC (no DMDAAC monomer present) In a network of poly(Nvlnylpyrrolldone)/N-vlnylpyrrolldone.
* To whom a l l correspondence should b e addressed.
The modification of electrode surfaces with polymer films has been an active area of research in the past decade (1,2). Ionomer membranes, with ionizable groups attached to organic polymer backbones, are the basis of a type of electrode modification based on ion-exchange processes. As a result of the electrostatic interactions a t the ion exchange sites, these membranes can exhibit a large difference in permeability toward oppositely charged ionic species in comparison to similarly charged species. The immobilization of ionomer membranes on electrode surfaces results in changes in both the sensitivity and selectivity of the electrode to the appropriately charged solution species (3). Du Pont's Nafion perfluorosulfonated polymer membrane has been the polymer of choice for many studies because it is commercially available, is water-insoluble, can be dip-coated
0003-2700/88/0360-2467$01.50/00 1988 American Chemical Society
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