High Temperature Seal for Gas Chromatography Detectors R. L. Faley and J. F. Long, Polychemicals Department, E. 1. du Pont de Nemours & Co., Victoria, Tex.
of a Crau-ford Swagelok tube U fitting to mount gas chromatogSE
raphy hot-wire detectors allows easy insertion and removal and ensures freedom from leaks or abnormal electrical noise from ambient temperature and pressure to 500" C. and 50 p.s.i.g. This mount has been in successful operation for over 2 years and can be applied to any block where Crawford fittings are adaptable. Electrical leads are carried into the detector block cavity by 22-gage tungsten wire swaged into 316 stainless steel tubing inch in outside diameter with magnesium oxide (Therm0 Electric Co., Inc., Saddle Brook, N. J.), A section of the tubing and magnesium oxide is stripped off to expose the tungsten wire, which serves as a support for the platinum filament (Figure 1). The detector block is fitted with a Swagelok male connector, modified by d a r g i n g the opening a t the pipe thread end to allow the stainless steel tubing to project '/,e inch below the
fitting when installed. A Swagelok '/4-inch nut, and front and back ferrule are slipped onto the tubing and positioned in the block. Details of mounting the detector will depend on the size of the detector block cavity. The length of tubing in the
block can be vsried to provide for positioning the filament a t any desired location in the gas stream. Leads to the measuring bridge are silver-soldered to the tungsten wire and the platinum filaments are gold-soldered or platinum spot-melded.
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Figure 1. A. 6. C.
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Exploded view of detector and mount F. G.
Detector block Modifled male connector Platinum wire Tungsten wire '/,-inch 0.d. stainless steel tubing
Magnesium oxide Front ferrule Back ferrule Nut Bridge leads
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Construction of long lengths of Coiled Glass Capillary D. H. Desty, J. N. Haresnape, and B. H. F. Whyman, Petroleum Division, Research Centre, The British Petroleum Co. Ltd., Sunbury-on-Thames, Midd lesex, England
on the application of capilIthexlary column gas chromatography in petroleum industry [D. H. Desty, A. WORK
Goldup, B. H. F. Khyman, J . Inst. Petroleum 45, 287 (1959)] some difficulty was encountered with adsorption on the wall of the metal tubes. It seemed worthwhile to examine tubes having an entirely different surface and to investigate the possibility of drawing long lengths of glass capillary. A versatile laboratory machine was developed, which can draw capillary having a wide range of diameters and wall thickness in lengths of several hundred feet coiled into the form of a compact helix. Such tubing probably has applications other than in gas chromatography. An application for patent protection has been filed. In an automatic drawing procedure a thick-walled glass tube, a few millimeters in diameter, is fed continuously into a heated zone, maintained a t a temperature high enough to cause the glass to flow. The fine capillary is then drawn continuously from the heated end of the tube a t a constant rate, greater than the tube feed rate by a factor appropriate to the reduction in
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ANALYTICAL CHEMISTRY
as the metal tube. The capillary then issues from the end of the bending tube as a close-wound helix and is collected on a suitable device. The detailed operation of the apparatus is shown in Figure 1. The parts are mounted on a thick brass plate and the original thick-n-alled glass tube is
cross section required. The straight capillary tube, which results from this operation, is passed into a heated metal tube bent into an arc, the temperature of a portion of the tube a t the entry point being maintained a t the lowest temperature necessary t o cause the capillary to bend into the same curve
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Figure 1.
Capillary apparatus
Brass base plate 2. Support 3. Thick-walled glass tube 4, 5. Feed rollers 6,7. Rubber tires 8. Furnace 9, 10. Draw rollers 11. Porcelain tube 12. Bending tube 13. Bending tube support and earth connection 14. Connection to low voltage transformer 1 15. Connection to low voltage transformer 2 16. Furnace support and earth connection 1.
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