The Modern Student laboratory: Chromatography A Semipreparative Gas Chromatography Collection Tube Adapter Sang-Ho Lee and Martin ~ u l c e ' University of Maryland Baltimore County, Baltimore, MD 21 228 Semipreparative gas ~hmmatography~.~ using gas chromatographs equipped with 114-in. packed columns and thermal conductivity detectors is a useful technique for the isolation of tens of milligrams of volatile compounds from complex matrices. Compounds purified by this technique typically provide excellent NMR, W-vis, and IR spectra as well as good combustion analyses. Consequently, semipreparative gaschmmatography is a useful addition to both organic teaching and research labo~atories.~.~ Methods to attach glass collection tubes to the heated thermal conductivity detector exit ports of a gas chromatograph vary accordingto the specificdesign of the port: ports equipped with a septum nut employ a septum with a 2-5-mm hole through which a glass collection tube can be inserted, while other threaded ports can use a standard taper adapter for attachment of a collection tube. Port designs ending in a simple metal tubulation require more ingenuity to provide effective collection tube attachment, such as use of insulated Swagelok fittings. In all cases, minimal dead volume between the detector and collection
Assembled and exploded views of collection tube adapter. tube is important in order to minimize fraction overlap and sample condensation. A convenient and general method for collection tube attachment to detector exit ports uses flanged Teflon tubing for attaching commercially available (Ace Glass 9579-06) collection tubes with T 515 joints. To illustrate, a collection adapter for a Shimadzu GC-8AIT gas chromatograph can be prepared from an appropriately threaded nut with a 5-mm hole (Shimadzu 201-30008), a length of 5- or 4 m m (VWR 63014043) Teflon tubing, and a silicone O-ring gasket (Shimadzu 201-476141, as seen in the figure. Using a flanging tool (VWR 655140031, an 8- or 9-mm flange is created on a 1-or 2-cm piece of Teflon tubing. A silicone O-ring is slipped over the narrow end of the tubing and is placed snugly against the inside face of the flange. The flaneed tube is inserted into the nut so that the narrow end of tce tubing protrudes through the 5-mm hole in the nut. This assembly is threaded on to one of the detector exit ports until snug, providinga gas-tight seal. The narrow end of the tubing then is trimmed using a sharp razor blade so that about 3 mm of tubing protrudes from the nut. The T 515 inner joint of the collection tube is fully inserted into the Teflon tubing of the adapter when collecting detector effluent, providing a gas-tight seal of low dead volume and ease in changing ofcoilecti& tubes. In practice, the silicone and Teflon components of the adapter are useful to 250 "C, which is sufficient for many puiposes. This simple desim can be modified to be suitable for any threaded exit detictor port, given the appropriate nut. Unthreaded exit ports can be accommodated by creating an appropriate flange at the end of the Teflon tubing, which can be slipoed over the exit port. Use of the c o m t i d . Teflon tub;;(: when assembling the adapter allows for use of non-standard-taper collection tubes made from standard 0.d. glass tubing. 'Author to whom correspondence should be addressed. Z(a)Willet, J.E. Gas Chromatography; Wiley: New York, 1987. (b) Grob, R.L. Modem Practice of Gas Chromatography; Wiley: New
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=McNair,H.M.; Bonelli, E.J. Basic Gas Chromatography, 5th ed.; Varian: Palo Alto, CA, 1969. Ya) Mayo, D.W.; Pike, R.H.; Butcher. S.S. Microscale Organic Laboratory, 2nd ed.; Wiley: New York, 1989. (b) Williamson, K.L. Microscale Oroanic Exoeriments:Heath: Lexinaton. 1987. 5~repararwe~as CiromarographKZlatws. Pretor~~s, V Eds.: Wlley-lnlersc~ence hew York, 1971
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Journal of Chemical Educatlon
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