904
Anal. Chem. 1981. 53. 904-905
plasticizer for the ionic cluster region in ionic polymers in that it increases the free volume of and decreases the polymer chain concentration in the ionic cluster. Therefore, as the water content of the cluster decreases, the polymer chain material should play an increasingly important role in determining the chemical environment of the cluster region. Since the T F E backbone in Nafion has an extremely low dielectric constant, it is not surprising that the ionic cluster resembles a lipophilic phase when a large organic cation is the counterion. In their investigations of the effects of plasticizers on sulfonate containing hydrocarbon polymers, Lundberg and his co-workers (22,23) point out (24) that stearic acid can act as both an ionic aggregate plasticizer (through its carboxylic acid end) and a chain plasticizer (through its CI7hydrocarbon chain). That is, stearic acid acts as a surfactant for the two phases in the ionic polymer. Since the large alkylammonium salts investigated here are also surfactants, interaction of the hydrocarbon part of the ammonium ion with polymer chain material outside of the ionic cluster may also be a factor contributing to the high affinity of Nafion for these ions. Spectroscopic evidence for interaction of ruthenium(I1) tris(bipyridine) ion with the fluorocarbon chains in Nafion has recently been presented (25). This work shows that it is possible to make an ISE using an ionic polymer as the ion-sensitive membrane. The advantage of the ionic polymer based electrode is that the membrane contains no water-leachable components and therefore this type of electrode should have much longer (essentially infinite) lifetime. Electrodes prepared 6 months ago are still functioning, and further evaluation of electrode lifetime is currently under way. This study, further, shows that the selectivity of the ionic polymer-based electrode can be quite high, comparable to that of conventional polymer membrane electrodes. Ionic conduction in the ionic polymer-based electrode presumedly occurs through the ionic cluster regions and the small channels connecting these regions. Yeager and Kipling (IO) conclude that for Nafion in the Cs+ form the small channels connecting the ionic cluster regions disappear and therefore diffusion through the TFE phase must occur. The question of con-
duction pathway, therefore, needs further investigation.
LITERATURE CITED Oesch, U., Simon, W. Anal. Chem. 1980, 52, 692. Cutler, S. G.; Meares, P.; Hail, D. G. J. Electroanal Chem. 1977, 85, 145. Covington, A. K. NBS Spec. Pub/. 1969, No. 374, 00. Keii, L.; Moody, 0. J.; Thomas, J. D. R. Analyst(London) 1977, 702, 274. Klmura, K.; Maeda, T.; Tamura, H.; Shono, T. J . Electroanal. Chem. 1979, 95, 91. Heineman, W. R. Anal. Chem. 1980, 52, 345. Holiday, L. In "Ionic Polymers"; Holllday, L., Ed.; Applied Science Publication: Essex, England, 1975; pp 30-35. Yeo, S.C.; Eisenberg, A. J . Appl. Polym. Sci. 1977, 27, 875. Gierke, T. D.. presented at the 152nd Natlonai Meeting of the Eiectrochemical Society, Atlanta, GA, Oct 1077. Yeager, H.'L.; Kipling, B. J . Phys. Chem. 1979, 83,1836. Yeager, H. L.; Steck, A. Anal. Chem. 1979, 57,862. Martin, C. R.; Freiser, H. Anal. Chem. 1979, 57, 803. Petrucci, S. "Ionic Interactions from Dilute Solutions to Fused Salts"; Academic Press: New York, 1971; Voi. I, p 43. Martin, C. R.; Freiser, H. J. Chem. Educ. 1980, 57, 512. Srinivasan, K.; Rechnitz, G. A. Anal. Chem. 1969, 47, 1203. Martln, C. R.; Freiser, H. Anal. Chem. 1980, 52, 562. Martin, C. R.; Freiser, H. Anal. Chem. 1980, 52, 1972. Marinsky, J. A.; Marcus, Y. "Ion Exchange and Solvent Extraction"; Marcel Dekker: New York, 1974; Voi. 6, p 15. Kraus, C. A. J . Phys. Chem. 1956, 60,129. Grot, W. G.; Munn, F.; Walmsley, G. E., presented at the 141st National Meeting of the Electrochemical Soclety, Houston, TX, May 1972. Steck, A.; Yeager, H. L. Anal. Chem. 1980, 52, 1215. Neuman, R. M.; MacKnight, W. J.; Lundberg, R. D. Polym. Prepr., Am. Chem. SOC.,Dlv. Polym. Chem. 1978, 79(2), 208. Lundberg, R. D.;.Makowski,H. S.; Westerman, L. Polym. Prepr., Am. Chem. SOC.,Dw. Polym. Chem. 1978, 19(2), 310. Makowski, H. S.; Lundberg, R. D. Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem. 1978, 19(2), 304. Lee, P. C.; Meisei, D. J . Am. Chem. SOC.1980, 702, 5477.
'
Present address: Deparment of Chemistry, Texas A&M University, College Station, TX 77843.
Charles R. Martin' Henry Freiser* Department of Chemistry University of Arizona Tucson. Arizona 85721
RECEIVED for review November 12,1980. Accepted February 12,1981. This work was conducted with financial assistance from the Office of Naval Research.
Liquid Chromatographic Fractionation of Isotopic p -Xylenes with Tetrakis(4-methylpyridine)nickel(II) Thiocyanate Sir: The versatility of the host tetrakis(4-methylpyridine)nickel(II) thiocyanate ( N i ( 4 - M e - p ~ ) ~ ( N c Sin) ~ ) forming inclusion compounds with many aromatic guests, and its use in separating isomers, first noted by Schaeffer and co-workers ( I ) , is well-known. In 1960 Kemula and Sybilska ( 2 )and in 1974 Lipkowski and co-workers (3)separated aromatic compounds by liquid chromatography (LC) using the same host as the stationary phase. While the separation of isotopic molecules such as C6Dfi-CfiHfi by gas chromatography (GC) ( 4 3 ) and by high-performance liquid chromatography (6,7) has been accomplished, there appear to have been no attempts to combine the two ideas, namely, to separate isotopic molecules utilizing inclusion. It has been shown by the present authors (8)that the selectivity of Ni(4-Me-py)4(NCS)2 extends to isotopic species, and we report the results of attempts to separate some protiated and deuterated isomers by
using a column of the complex as the stationary phase.
EXPERIMENTAL SECTION Reagents. The deuterated materials were the same as those used in the previous work (8). Procedure, The column preparation was similar to that of prepared Lipkowski and co-workers (3). The Ni(4-Me-py)4(NCS)z, by the method Logan and Carle (9), was analyzed for nickel, thiocyanate, and 4-methylpyridine and found to have a composition close to theoretical. One gram of it was dissolved in 32.5 mL of redistilled methanol (MeOH). To this was added 2.5 mL of redistilled 4-methylpyridine (4-Me-py)and 1.55 g of NH4NCS. To the resulting blue solution was slowly added 15 mL of distilled conwater with stirring, and particles of Ni(4-Me-p~)~(NCs)~, taining undetermined quantities of MeOH and 4-Me-py, of uniform size precipitated. The suspension was stirred for 1week and filtered. The column (0.4 cm diameter X 2 cm long) was slurry
0003-2700/81/0353-0904$01.25/00 1981 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 53, NO. 6, MAY 1981
Table I. Comparison of Mole Ratios, p-(CD,),C,D,/p-(CH,),C,,H,, before and after Chromatography
R1
a
Ro
0.792 0.988 0.819 0.988 0.988 0.782 0.731 0.988 0.735a 0.988 Larger volume of eluate used,
RS 1.079 1.146 1.112 1.064 1.198
Rs lR1 1.36 1.40 1.42 1.46 1.63
packed with the resulting solid sorbent and the filtrate from the packing used later as the eluting solvent. The column was loaded by injecting 30 pL of a solution of the isotopomers,p-(CD3)2C6D4 and P-(CH~)~C~H,, onto the top of it, and a thin layer, about 0.5 mm, of sorbent, deposited above this as a precaution against the tendency for the p-xylene layer to separate from the rest of the column. The sample was then eluted at a flow rate of 18 mL/h. The eluate was monitored for p-xylene by GC: as soon as the latter appeared collelction of the eluate was commenced and after it had disappeared collection was stopped. The latter event occurred after about 9 mL had been collected. At this point, the stationary phase was removed and decomposed with 6 N “21 and the p-xylenes were extracted with 0.5 mL of n-pentane. The 4.Me-py remained in the aqueous layer. The pentane layer was sub,jected to analysis with a CEC 21-104 analytical mass spectrometer as described in an earlier work (8). Similar analyses were performed on samples of the original protio-deutero mixture anld on the p-xylene-containing eluate. The apparent D/H ratios in the sorbent (R,J,the original mixture (Ro),and the liquid eluate ( R J were thus determined from the ratio of the areas of the parent peaks. Finally, these ratios were corrected to actual D/H ratios by reference to R calibration curve which had been established by using known mixtures. In a second series of similar experiments the sample size was varied. Moreover, this series included two other pairs of isotopic species: P-(CD~)~CBH~-P-(CH~)~C~H~ and P-(CD3)&D,-P(CD3)&&,, but the ratio R1 was not measured.
RESULTS AND DISCUSSI[ON
905
Table 11. Comparison of Mole Ratios, ~-(CD,),C,D~/P-(CH,)~~~~~,~-(CD,),C,H,/~~(~~~ and p-(CD,),C,D,/p.(CD,),C,H,, before and after Chromatography guests P-(CD3)2C6D4/ P-(CH,),C,H, P-(CD3)2C6H4/ P-(CH,),C,H4 P-(CDJ,C,D,/ P-(CD3)2C6H4
sample size, p L 25 30 40 50 50 30 30 30 30
R,
0.916 0.916 0.916 0.916 0.922 0.922 0.922 0.922 1.02
RS 1.29 1.24 1.18 1.16 1.26 1.33 1.31 1.33 1.03
RS I Ro 1.41 1.3 5 1.29 1.27 1.37 1.45 1.42 1.44 1.01
freshly prepared column which had had no previous contact with p-xylene. With R, = 0.922,R, on the first column was found to be 1.12and, on the second, 1.15.This increase was unexpected and is unexplained. The following solvent mixtures were tried in an effort to find one which would actually separate the members of each pair of guests: n-pentane, methylene chloride, acetonitrile, and ethyl acetate, each containing 4-Me-py and with varying proportions of n-pentane and water. None was successful. Nevertheless, it is clear that fractionation had occurred in the systems reported. It is particularly noteworthy that the more deuterated isomer is more firmly held on the column. This is the opposite of the effect noted by previous workers in their investigations using GC ( 4 , 5 )and EC (6, 7) and not based on inclusion phenomena. In these latter studies the more deuterated isomer was found to be less firmly held and so eluted first.
ACKNOWLEDGMENT We thank Moses K. Kaloustian of our department for helpful discussions.
LITERATURE CITED
The results of the first series of experiments are presented (1) Schaeffer, William D.; Dorsey, W. S.; Skinner, Davis A.; Christian, C. in Table I. The R values we estimated to be accurate to about G. J. Am. Chem. SOC. 1957, 79, 5870-5878. 1%. Also shown are the vidues of RJR1 which may be taken (2) Kemula, Wiktor; Sybllska, Danuta Nature (London) 1060, 185, 237-238. as a measure of the separation attained. It is\ evident that the (3) Lipkowski, Janusz; Lesniak, Karol; Bylina, Andrzej; Sybllska, Danuta; deuterated isomer is retained on the column t o a greater extent Duszczyk, Kazimiera J . Chromafogr. 1074, 9 1 , 297-302. (4) Bruner, F.; Cartonl, G. P. J . Chromatogr. 1083, 10, 396. than the protiated and, as expected, the effect is larger than (5) Llberti, Arnoldo; Cartonl, Gian P.; Bruner, Fabrizlo J . Chronlatogr. that found in the previous single stage, nonchromatographic 1983, 72, 8-14. experiments (8) where the equilibrium value of R,/R1 was (6) Cartonl, G. P.; Ferretti, Ivo J. Chrornatogr. 1078, 122, 287-291. (7) Tanaka, Nobuo; Thornton, Edward 8.J. Am. Chem. SOC.1978, 9 6 , about 1.10. 1617- 16 19. Table I1 gives the results of the second series of experiments. (8) Ofodile, Samuel E.; Kellett, Richard M.; Smith, Norman 0. J. Am. Chem. SOC. 1979, 101, 7725-7726. In R, and R, the numerator is the more highly deuterated of (9) Logan, Albert V.; Carle, Don W. J. Am. Chem. SOC. 1052, 74, the pair, as it is for Table 1. Again, the latter is more firmly 5224-5225. held on the column. The magnitude of R,/Ro is seen to inSamuel E. Ofodile crease with diminution in r~amplesize. The effectiveness of Norman 0. Smith* the separation in the systeim P - ( C D ~ ) ~ C ~ H ~ - ~ - ( CisH ~ ) ~ C ~ H ~ Department of Chemistry about the same as i t is in the system p-(CD3)2C6D4-pFordham University (CH3)&& but barely noticeable for p-(CD3)2C6D4-pNew York, New York 10458 (CD3)2C6H4. This suggests that the selectivity is determined only by the hydrogen atoms of the methyl groups. In a further experiment, using p-(CD:&D4 and p RECEIVED for review October 13, 1980. Accepted February (CH&C6H4 with R, = 0.838,the column after elution was 2,1981. This material is taken from the Ph.D. dissertation divided into the upper and lower portions, and the R, values of S. E. Ofodile, Fordham University, Feb 1980. It was were determined for both. This yielded R = 1.135and 0.973 presented to the Division of Physical Chemistry of the Amfor the two parts, respectively. This is underatandable if the erican Chemical Society in Washington, DC, Sept 1979,and (undetermined) R1 for the upper portion of the column be at the International Symposium on Clathrate Compounds and regarded as the R, for the lower portion. Molecular Inclusion Phenomena, held in Jachranka (Warsaw), Lastly, an experiment was performed, using a p Poland, Sept 1980. Acknowledgment is made to the donors (CD3)2CsD,-p-(CH3)2C6H4 mixture, in which the entire eluate of The Petroleum Research Fund, administered by the Amfrom one chromatographic treatment was passed through a erican Chemical Society, for support of this research.
