that in our experiments the fraction of surface covered by solute molecules a t the column outlet did not usually exceed 0.05%. Even with this small coverage, the adsorption sites were heterogeneous. According to the calculations of Colin and Guiochon (ref. 6, p 52) our adsorbent, with 15% carbon, carried twice as much carbon as was needed to form a monolayer on the surface of the silica base. Electron microscopy indicates that the surface is completely covered with carbon, but Colin and Guiochon point out that it is very likely that some silica is exposed. Probably the carbon is bonded to silica through silicon-carbon bonds, and the surface has some of the character of twodimensional silicon carbide, as well as that of carbon and of silica. The strong 2-effect suggests the presence of two-dimensional basal planes of graphite. No x-ray lines of graphite nor of silicon carbide were seen, so there can be no significant amounts of these materials as bulk crystalline phases. It is easy to understand why the surface of pyrocarbon-silica is heterogeneous. It is not so easy to understand why the 2-effect is so much stronger on this material than on graphitized carbon black. In spite of its heterogeneity, pyrocarbonsilica shows great selectivity among isomeric chlorinated biphenyls and great promise as a chromatographic absorbent. It would be worth testing materials with a somewhat higher proportion of carbon, in hope of finding a more uniform surface, and materials of smaller particle size, which should give narrower bands. With even a modest improvement in column performance, liquid chromatography on pyrocarbon-silica could give resolution equal to capillary gas chromatography for a t least the lesshighly chorinated biphenyls. The technique is easier than that of capillary gas chromatography, and its sensitivity could be improved by using lower wavelengths for ultraviolet detection. One could also pass the effluent directly into an electron-
capture detector, as was done by Willmott and Dolphin (16).
ACKNOWLEDGMENT We cordially thank H. Colin and G. Guiochon for the gift of carbon black and pyrocarbon-silica absorbents and for discussions in their laboratory. We also thank K. Fujita of Hitachi, Ltd., for the gift of polystyrene gel, and Curt Haltiwanger of the University of Colorado for the x-ray diffraction study.
LITERATURE CITED T. Hanai arid H. F. Waiton, Anal. Chem., 49,764 (1977). T. V. Barmakova, A. V. Kiseiev. and N. V. Kovaleva. Kolbidn. Zh.. 36.
133, 934 (1974). E. V. Kaiashnikova. A. V. Kiseiev. D. Poskus. and K. D. Shcherbakova, J . Chromatoor. 119. 233 (1976). H. Colin. C. Eon, and G . Guiochdn, J . Chromatogr., 119, 41 (1976). H. Colin, C. Eon, and G . Guiochon, J . Chromatogr., 122, 223 (1976). H. Colin and G. Guiochon, J . Chromatogr., 126, 43 (1976). N. K.Bebris, R. G. Vorobieva, A. V. Kiseiev, Yu S.NikRin, L. V. Tarasova. I. I. Frolov. and Ya. I. Yashin, J . Chromatogr., 117, 257 (1976). R. G.Webb and A. C. Mccall, J . Assoc. Off. Anal. Chsrn., 55,746 (1972). R. G. Webb and A. C. McCall, J . Chromatogr. Sci., 11, 366 (1973). J. Krupcik, P. A. Leclercq, A. Simova, P. Suchanek, M. Collak, and J. Hrivnak, J . Chromatogr.. 119, 271 (1976). U. A. Th. Brinkman, J. W. F. L. Seetz, and H. G. M. Reymer, J . Chrornatoyr., 116, 353 (1976). U. A. Th. Brinkman, A. de Kok, G. de Vries. and H. G. M. Reyrner, J . Chromatogr., 128, 101 (1976). U. A. Th. Brinkman and J. J. de Kok. Fresenius' Z . Anal. Chem.. 283, 205 (1977). D. L. Stalling and J. N. Huckins, J . Assoc. Off. Anal. Chem., 54,801
(1971). D. Sissons and D. Welti, J . Chrornatogr., 60, 15 (1971). F. W. Wiiimotl and R . J. Dolphin, J . Chromatogr. Sci., 12, 295 (1974).
RECEIVED for review May 27,1977. Accepted August 5, 1977. Support is acknowledged from the National Science Foundation, Grant CHE 76-08933. Part of this work was presented a t the ACS Award in Chromatography Symposium, New Orleans, La., March 21, 1977.
Dynamic Slurry-Packing Technique for Liquid Chromatography Columns H. P. Keller, F. Erni, H. R. Linder, and R. W. Frei"' Analytical Research and Development, Pharmaceutical Division, Sandoz, Ltd., 4002-Basle, Switzerland
A new packlng apparatus for slmultaneous packing of up to 6 columns Is descrlbed. The principle Is based on a comblnation of stirrlng action and high pressure of up to 500 bar. Data are presented for packlng reversed phase materlals. The choice of slurry solvent Is not critical and nontoxic inert and moblle phase compatible solvents can be used. A column testing procedure whlch takes Into account both plate heights and asymmetry Is discussed wlth a serles of C8 reversed phase columns packed for routine use. The method will provlde columns wHh good separation properties for a column length of up to 25 cm.
It is usually accepted that particles of 5-10 km particle size have to be packed by slurry techniques. Solvent systems with Present address, Department of Analytical Chemistry, The Free University at Amsterdam, De Boelelaan 1083,NL Amsterdam 1011, The Netherlands. 1958
ANALYTICAL CHEMISTRY, VOL. 49, NO. 13, NOVEMBER 1977
suitable equal density or viscosity properties are used to keep the particles in a reasonably suspended state during the packing procedure (1-3). In the very recent literature an alternative method was proposed where silica gel and alumina particles of 3-6 km were packed upward with methanol as a slurry solvent. The pressure was ZOO0 psi using a CE 210 coil pump. The column dimensions varied between 10-100 cm length and 1 5 mm i.d. Because of the few experimental data published, it is difficult to make a comparison with the method presently discussed. In our laboratories a new packing principle has been described (4)which involves a combination of high pressure and stirring action to keep the particles afloat during the column-filling step. The advantages of this principle were primarily the elimination of inconvenient halogenated solvents and the possibility of using slurry solvents similar to the mobile phase which shortens the time of eauilibration for the columns mior to actual use. The disadvant&e was that the quality of coiumn Packing decreased drastically with increasing column len@h, and it has been demonstrated experimentally ( 4 ) that only
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