In a study describing electrolytic conduction in ionic glasses, Hamman (4)demonstrated that an excellent correlation existed between the experimentally measured AV and the calculated V , of the mobile, cationic charge carriers. In a similar manner, Sasabe et al. (8) determined activation volumes for conduction which suggested that segmental motion in polymers was responsible for transport of electrical current through poly(viny1 acetate) films. As the values listed in Table I show, good correlation exists between conduction activation volumes and the molar volume of the respective anion calculated from crystallographic data. One may therefore conclude that the charge is anionically transported through the bulk resin by the anion with the experimentally measured AV corresponding to a process in which compression retards ion migration by decreasing vibrational and oscillatory motions of polymer segments resulting in an increased local viscosity. Since the cationic resin species is immobilized, it probably does not contribute to the observed conductivity. In an earlier study of poly(viny1 chloride) films doped with the quaternary ammonium salt, methyltricaprylylammonium chloride, pressure-conductivity measurements yielded corrected AV values of 34 f 2 cm3/mol. In contrast to the ion exchange materials, the cation in this system is not chemically bonded to the polymer and despite its relatively low mobility should be expected to contribute to the electrical conduction process. One could very roughly estimate the contribution such as an additional charge carrier would make to the calculated activation volume by taking the summation of individual
molar volumes multiplied by their respective, weighted transport numbers (assumed to be proportional to the reciprocal of the molar volume). As a limit of relative ion sizes (cation volume >> anion volume) such a calculation would give a value of twice that of the anion volume. While this approximation is admittedly rather crude, it nonetheless suggests the earlier results are reasonable in view of this present study. The conduction process in both the poly(viny1chloride)quaternary ammonium salt system and the ion exchange resins resembles that in liquids where activation volumes for selfdiffusion are generally one molar volume or greater (9,10). In solids and crystalline materials, it is usual to find AV < V,. A theory (11)based on defect formation in solids suggesta that AV N ‘lZV, would be reasonable.
LITERATURE CITED (1) F. Heifferich, “Ion Exchange”, McGraw-Hill, New York, N.Y., 1962. (2) G. D. Carmack and H. Freiser, Anal. Chem., 45, 2249 (1975). (3) S.Saito, H. Sasabe, T. Nakajima, and K. Yada, J. Polym. Sci., 8 , 1297 (1966). (4) S.D. Hamann, Aust. J. Chem., 18, l(1965). (5) D. D. Eley, J. Polym. Sci., Part C, 17, 73 (1967). (6) N. A. Lange, “Handbook of Chemlstry”, McGraw-Hill, New York. N.Y., 19fi7 n 129 r
(7) Prk’Datta, J. Sc/. Ind. Res., 30, 222 (1971). (8) H. Sasabe, K. Sawamura, S. Saito, arid K. Yada, Polym. J., 2, 518 (1970). (9) J. Naghizadeh and S. A. Rice, J. Chem. Phys., 38, 2710 (1962). (10) A. F. M. Barton, B. Cleaver, and G. J. Hills, Trans. Faraday Soc., 84, 208 11968). (11) R. W‘. Keyes, J. Chem. Phys., 29,467 (1958).
RECEIVED for review December 13,1976. Accepted February 4,1977. This work was supported by a grant from the Office of Naval Research.
Gas-Solid and Gas-Liquid Chromatography Using Porous Layer Open Tube Columns Made with Graphitized Thermal Carbon Black C. Vidal-Madlar, S. Bekassy,’ M. F. Gonnord, P. Arpino, and Georges Gulochon” Ecole Polytechnique, Laboratoire de Chimie Analytique Physique, 9 1128 Palaiseau Cedex, France
A slmgle method for preparatlon of porous-layer open tubular columns uslng graphltlzed thermal carbon black is described. The adsorbent is coated as a thin layer on the walls of the column. I n gas-solid chromatography the columns show high selectlvlty for geometrlcal Isomers, and allow dlfflcult separations at temperatures lower than with clasdcal columns. The columns are highly permeable and can be coated by percolation with various polar or apolar statlonary phases without dlsturblng the carbon layer. By changing the nature or the concentration of the statlonary phase, a range of selectlvltles may be obtained from that of the pure graphltlzed thermal carbon black support to that of the pure llquld statlonary phase. W4h high liquld phase loadings the columns are very selective, very stable, and accept large samples. They have also been used successfully for trace analysis In GC-MS. Present address, I n s t i t u t e f o r Organic Chemical Technology, T e c h n i c a l University, 1521-Budapest, Hungary.
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Porous layer open tubular columns (PLOT) with graphitized thermal carbon black (GTCB) coating present many advantages in gas chromatographic analysis over conventional columns packed with the same adsorbent (1,2):the relatively low amount of adsorbent introduced into the column reduces the analysis time. Alternatively, a given compound may be eluted in the same time at a temperature about 100 “Clower than with classical columns (I). Furthermore, high efficiencies can be achieved with long capillary columns, as the pressure drop is low because of the unrestricted flow of carrier gas. The support for the liquid stationary phase in PLOT columns is now generally introduced into the capillary column ilsing the simple methods of dynamic coating. Capillary columns with various support coatings such as silica (3), diatomaceous earths (4), inorganic salts (5), and GTCB (6) have been prepared by this method. On the other hand, PLOT columns made with GTCB and used for gas-solid chromatography are prepared by a static coating procedure similar to the one described by Halasz and
t(rnin.)
14
12
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Flgure 1. Analysis of xylene isomers on unmodified GTCB Sterling FTG Column length: 19 m, temperature: 165 O C , pressure drop: 0.5 atm, carrier gas: helium
EXPERIMENTAL Pyrex glass capillary columns of 0.50-mm i.d. were drawn using a machine similar to the one described by Desty et al. (14). A 5 % (w/w) suspension of graphitized thermal carbon black Sterling FTG (Cabot, Billerica, Mass., specific surface area 13 m2 g-I) in a solution of Squalane 0.05% (w/w) in methylene chloride is forced under pressure into the column. The flask containing the suspension is connected t o the glass capillary column with a Swagelok fitting containing a metallic sieve. Squalane in solution acts as a dispersive material for the carbon black particles and thus stabilizes the suspension for about 24 h. When the column is filled with the suspension, one end is carefully sealed with a microburner. The open end of the capillary column is introduced into a drying apparatus similar to the one described by Ilkova and Mistryukov (15),and the solvent vaporizes at 140 "C while the column enters slowly into the oven. A thin carbon black layer is then formed on the walls of the column. The amount of GTCB SterlingFTG introduced into the column depends on the concentration of the suspension used. Most often it was about 10 mg/m of capillary column. The column is heated overnight at 220 "C under a nitrogen stream and then washed with a slow stream of methylene chloride in order to eliminate the squalane completely. This operation is easily carried out without destroying or appreciably disturbing the GTCB layer. A GTCB capillary column is obtained whose properties are similar to those described in our previous work ( I ) . Figure 1shows the separation of light aromatic hydrocarbons. The elution order of the xylene isomers (rn and o + p ) is characteristic of gas-solid chromatography on GTCB, and different from the one observed on most liquid phases. The same static coating procedure has been used to coat the GTCB layer with a liquid stationary phase. The percentage of liquid phase coated on GTCB depends on the concentration of the solution. Without disturbing the carbon layer, the classical
*
6
2
il
b
Horvath (7), which seems to be the most suitable method as it permits a better control of the amount of adsorbent introduced in the column and a better homogeneity of the adsorbent layer. By coating graphitized thermal carbon black on the walls of open tubular capillary columns, we have obtained columns which permit very fast analysis while offering a high degree of selectivity for geometrical isomers (1, 2 ) . We have also shown that phthalocyanine-coated GTCB make very good adsorbents which can be used to prepare PLOT columns (8). GTCB modified with small amounts of a liquid stationary phase is useful in the analysis of polar compounds as shown by Bruner, Di Corcia, and their co-workers (9-11). By changing the amount and the type of the liquid phase, it was possible to achieve a whole range of selectivities (9-11). Until now the modified adsorbent has been used to pack conventional (12) and micropacked capillary columns (13). In this work we discuss the preparation and applications of PLOT columns made with GTCB modified with various polar liquid phases or coated with large amounts of these stationary phases.
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I
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Analysis of xylene isomers on GTCB. (a)Sterling FTG modified with ca. 0.1 % Carbowax 20 M. Column length: 7 m, temperature: 91 O C , pressure drop: 0.5 atm, carrier gas: helium. (b) Sterling FTG modified with ca. 0 . 4 % Carbowax 20 M. Column length: 19 m, temperature: 90 O C , pressure drop: 0.5 bar, carrier gas: helium Flgure 2.
dynamic procedure can also be used successfully for impregnating GTCB with large amounts of stationary phase. Columns prepared by this method have typically 1000 plates per meter for retained compounds (12' = 3) which corresponds to a reduced plate height of two column diameters. This efficiency can be increased by using capillaries of lower internal diameter. The columns are connected to metal capillaries (Talmant tubes, Pantin, France, Dilver P, 0.2-mm i.d., 0.4-mm 0.d.) with a Kovar Pyrex type connection. The column is then easily connected to the gas chromatograph with Swagelok fittings. The instrument has a flame ionization detector and a splitting system which allows the injection into the column of a sample between 0.1 and 10 pg as a narrow plug. The carrier gas is helium.
RESULTS GTCB Modified with Small Amounts of Stationary Phase. Carbowax 20 M. GTCB has been modified with ca. 0.1% w/w of Carbowax 20 M coated from a dilute solution (0.004% w/w in methylene chloride). This low percentage of Carbowax is enough to change dramatically the adsorption properties of GTCB, as shown on Figure 2a. The three xylene isomers are completely separated, whereas p - and o-xylenes are not resolved on pure GTCB (Figure 1). The primary retention mechanism on this modified adsorbent, however, stili seems to be adsorption, as the retention pattern on this phase is similar to that observed in gas-solid chromatography, with copper phthalocyanine on GTCB (16). With a higher percentage of Carbowax 20 M (ca. 0.2% w/w), the adsorption properties are still about the same and the xylene isomers are well resolved. With a higher amount of stationary phase (ca. 0.4% w/w), the resolution of m- and p-xylene decreases (Figure 2b). At low surface coverage ratios of the stationary phase (about 0.5% of Carbowax 20 M is necessary to form a monolayer (17)),the selectivity depends very much on the coverage ratio so that a wide range of selectivities can be observed. This is caused by the existence of two different adsorption mechanisms which are superimposed: the first one is the nonspecific adsorption of molecules on GTCB which depends mainly on the molecular weight, the polarizability, and the geometrical structure of the molecule (18),while the second mechanism is the specific interaction between the functional groups of the liquid phase and those of the molecule. The low amount ANALYTICAL CHEMISTRY, VOL. 49, NO. 6, MAY 1977
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4.
/cH4 5i6
I
;4
--I--+
6
2
4
+
0
Figure 3. Analysis of polynuclear aromatic hydrocarbons on GTCB Sterling FTG modified with ca. 0.4% polyphenyl ether sulfone. Column length: 13 m, temperature: 290 OC, pressure drop: 0.5 atm, carrier gas: helium. (1) solvent, (2) naphthalene, (3) biphenyl, (4) acenaphthene, (5) fluorene, (6) c-terphenyl, (7) carbazole, (8) phenanthene, (9) anthracene, (10) mterphenyl, (11) pterphenyl
t (mln)
2
lo
1
Flgure 6. Separation of aromatic hydrocarbons on GTCB modified with
ca.0.4% polyphenylether sulfone. Column length: 13 m, temperature: 140 OC, pressure drop: 0.5 atrn, carrier gas: helium
I t
2.4+ 2.5 DMP
I
I
d
6
t h n )
0
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Flgure 4. Separation of acenaphthene and biphenylene on GTCB Sterling FTG modified with ca. 0.4% polyphenyl ether sulfone. Column length: 13 m, temperature: 280 OC, pressure drop: 0.5 atrn, carrier gas: helium. (1) solvent, (2) naphthalene, (3) biphenyl, (4) acenaphthene, (5)biphenylene, (6) fluorene, (7) c-terphenyl
Flgure 7. Analysis of dimethylphenol isomers (DMP) on GTCB coated with ca. 2% Carbowax 20 M. Column length: 27 m, temperature: 170 OC, pressure drop: 0.5 atrn, carrier gas: helium
4 Solvent
t
I'
I
2 4 D M P t 2 5 DMP 2 3 6 TMP
i
4
t (mtn) 50
40
30
20
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0'
Figure 8. Analysis of methyl and polymethylphenol isomers on GTCB coated with ca. 20% Carbowax 1500 (MP = methylphenol, DMP = dimethylphenol, TMP = trimethyiphenol). Column length: 20 rn, temperature: 170 OC, pressure drop: 0.5 atm, carrier gas: helium
0
2
4
6
8
t (mi".)
Flgure 5. Separation of nltrogen compounds on GTCB modified with ca. 0.4% polyphenyl ether sulfone. Column length: 13 m, temperature: 289 OC, pressure drop: 0.5 atm, carrler gas: helium. (1) quinoline, (2) 4,4-bipyridine, (3) acenaphthene, (4) carbazole
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of stationary phase deposited, however, is not sufficient to deactivate appreciably either the glass surface of the capillary or the active sites of the carbon black as polar compounds like alcohols are eluted with unsymmetrical peaks. Polyphenyl Ether Sulfone. Polyphenyl ether sulfone is an interesting new phase which is polar and stable a t high temperatures (19,20).Because GTCB is also stable (I), the use of this liquid modifier is quite promising. Figure 3 shows that phenanthrene and anthracene are separated in four minutes on GTCB modified with polyphenyl ether sulfone, as they are on pure GTCB. The advantage of the modified adsorbent, however, is demonstrated by the elution of carbazole as a relatively symmetrical peak while on pure Sterling FTG, carbazole is eluted as a broad and unsymmetrical peak
