A Simple Method for Reducing the Breakage of Glass Columns in Gas Chromatography Glass columns are routinely used in gas chromatography and gas ehramatography/mass spectrometry analysis of many biologically important compounds. These columns have the advantage of being quite inert (after washing with a silylating agent prior to packing) to labile compounds such as catecholamines, steroids, drug metabolites and pesticides and easy to pack via the suction technique. Further, since they are transparent, any gaps in column packing, which would result in loss of efficiency, are easily detected and corrected. A major disadvantage is their fragile nature. Metal and Teflon columns have sufficient flexibility to withstand the stresses oi column installation, normal instrument vibrations and expansion and contraction during heating and cooling periods; glass columns, on the other hand, often crack under these conditions. We have designed a simple device that circumvents the breakage problem and gives the column flexibility without loss of inertness.
GLASS
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The end of the glass column is connected to a brass union as shown in the illustration. The union can either be a ' / r in. ta ' / r in. or a I/+ in. to '/a in. reducing union. The union is in turn connected to a short piece of Teflon tubing (1.3-1.5 in. in length). The Teflon tubing is then connected to the injection port or detector fittings. Thick-walled Teflon tubing must be used since this has less tendency to collapse a t the end and cause a blockage, or to "cold flow" which requires constant tightening to prevent leaks. (Suitable thick-wall Teflon tubing can he obtained commercially from Scientific Glass Co., Bloomfield, New Jersey.) When using a 'In in. to '/+ in. union, ' I sin. i.d. (3mm)/0.03 in. wall tubing is best; with a ' I r in. to 'Is in. reducing union, 3/32 in. i.d. (2mm)/0.03 in. wall tubing is best. The Teflon ferrules used need not he the preformed commercially available type but can be made in situ by wrapping a narrow strip of Teflon ribbon dope thread sealant (Permacel) around the glass or Teflon tubing and tightening the appropriate Swage-Lok fitting. The tape molds itself to the shape of a ferrule. Should a leak develop the tape can easily be removed and replaced. The column is then packed by the usual procedure to the end of the Teflon part of the column. The passage of vaporized sample through the short i 3 / r in.) brass union appears to cause no decomposition of the sample components. The increased flexibilitv of the column causes it t o rest on the eratine .. .. over the heating elements and fan of the o w n . To pre\rrnt "hot spotsMin the column that rno) rriult i n h i e of rfuciency and rerdsmg power n narmv pad 01 Pyrex brand glass wcol n placed under the rolumn rmrlnp. 11shghrlv f r . m rhs hrnt aourrr ~~
Institute of Rehahililalion Medicine New York liniversity Medical ('enter New York, N e w Yurk LUOiti
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M. Alice Becker N. Eric Naftehi
Volume 52. Number 2, February 1975
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