Gaskets for Glass Columns Used in Gas Chromatography at Temperatures above 300 "C Morton Beroza and M. C. Bowman U . S. Department of Agriculture, Agricultural Research Seroice, Beltsuille, Md. 20705 and Tifton, Ga. 31794 IN USING the new thermally stable polycarboranesiloxane stationary phase, Dexsil 300 (Analabs, Inc., North Haven, Conn.), at temperatures up to 400 "C in the gas chromatographic analysis of pesticides, the silicone O-rings used to seal the glass columns deteriorated rapidly. This difficulty was overcome by using asbestos gaskets impregnated with Dexsil 300 prepared as follows: Separate the 3 strands of a length of W. H. Curtin & Co. (Houston, Texas) No. 1444A l/ls-inch 0.d. asbestos cord, dip the strands into a solution of Dexsil 300 in chloroform, and hang them in a hood to dry. On the glass column (6 mm 0.d. in this example) place a '/r-inch stainless steel Swagelok nut and back ferrule turned backward, and wrap a 30-cm length of the strand on the glass tubing where the seal is to be made. See Figure 1. Tighten the nut firmly against the asbestos gasket with a wrench to effect the seal, taking care not to crush the glass. Raise the temperature of the oven to 150 "C for 5 minutes and tighten the nut again. Finally bake at 300 "C until the base line becomes constant. If response and retention times
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ANALYTICAL CHEMISTRY, VOL. 43, NO. 6, MAY 1971
ASBESTOS GASKET
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Figure 1. Assembly with high-temperature gasket are the same as those obtained with silicone O-rings (checked in advance for a given solution), the seal is good. Once formed, the asbestos gasket keeps its shape and does not have to be replaced when the column is removed. RECEIVED for review February 1, 1971. Accepted March 1, 1971. Mention of proprietary products is for identification only.
