Table I. Comparison of Degassing Rates Liquid Water Benzene Olive oil
Fast stirring 28 min for 5 p 20 min for 5 p 30 min for 5 p
Slow stirring 38 min for 5 25 min for 5
...
p p
Liquid transfer to trap 1 cm3 17 cm3 0 cm3
For a nonvolatile liquid, the entire system (S3, S4 open) is pumped on for 2 minutes, S4 is closed and the pressure is read after 1 minute. The procedure is repeated until the base pressure is attained. COMPARATIVE TESTS
Our test liquids were water, benzene, and olive oil (the same as in I and 11). The results of comparative tests are shown in Table I. The time shown is the time necessary to attain the base pressure (as indicated) by using the appropriate procedure. In contrast to I and I1 olive oil degassed faster with the current design. On the other hand, this apparatus was significantly less efficient than I and I1 for benzene, but better than I for water. However, thoroughly degassing 500
cm3 of a liquid in 30 minutes or less is still a very convenient procedure. This is especially the case considering the small amount of liquid transferred to the trap. The current design also permits transfer of degassed liquid under exclusion of the atmosphere via stopcock S2 to another vessel. A second version of the apparatus (Figure 2) gives results comparable to those shown in Table I. It was fabricated from a 3-liter erlenmeyer flask. Fast stirring using an egg-shaped stirring bar creates a vortex and forces liquid up the wall exposing a large surface area to vacuum. CONCLUSIONS
The apparatuses shown in Figures 1 and 2 will degas 500 cm3 of a volatile or nonvolatile liquid down to a residual gas pressure of 5 p in 30 minutes or less. They are simple to fabricate and operate and can be readily scaled up or down to handle other quantities of liquids. RECEIVED for review October 16, 1970. Accepted January 28, 1971. This work was supported by Public Health Service Grant No. G M 14710-04. E. W. is a Senior Fulbright Research Scholar on leave of absence from the University of Vienna, Vienna, Austria.
Simple Matallic Connection of Glass Capillary Columns to Chromatographs Jacqueline Ganansia, Catherine Landault, Claire Vidal-Madjar, and Georges Guiochon Ecole Polytechnique 17, rue Descartes, Paris, France 5’
CONNECTING GLASS capillary columns to gas chromatographic instruments is always difficult: the glass is brittle, column flexibility is limited, and the connections have to withstand in most cases high temperatures while remaining leakproof. For this reason, metallic columns are often preferred to glass columns in spite of the lower cost and better performance of the latter. In our laboratory, we are using metallic capillary tubes of a special alloy, Dilver P, which can be sealed to borosilicate glass (1). The outer diameter of the tube is small enough to be introduced in the glass capillary column (o.d., 0.4 mm; i.d., 0.2 mm). The chromatographic packing material must be removed from both ends of the column for a distance of 1-1.5 cm when packed capillary or thin-layer open tubular columns are used. This is easily done using a thin wire. Next the end of the metallic capillary tube is heated in a tiny oxidizing flame to form a thin coating of oxide over a length of about 1 cm. It is then introduced in the glass capillary column. A micro burner with three convergent small flames ( 2 ) is used for the sealing. The glass is first sealed at the tip of the metal tube protruding (1) J. Talmant, 87, rue de Paris, 93 Pantin, France.
(2) C. Landault, Thesis, University of Paris, 1967.
into the column and then the glass is slowly melted toward the outlet of the column. At the other end of the metallic capillary tube, a metallic tube of a larger diameter can be soldered. This allows connection of the column to the instrument with the usual metallic fittings ( l/le-inchSwagelok for example). No loss of efficiency has been observed as dead volumes are reduced to a minimum (3): the metal capillary tube can be introduced right into the injection port and into the detection device (in the burner tip if a flame ionization detector is used). Fittings prepared this way are usually leakproof at inlet pressures of 10 atm. We have also experimented with this kind of connection at very high temperatures, using gas-solid chromatography ( 4 ) to separate polynuclear aromatic hydrocarbons. No leak occurs, until around 600 “C,where the glass column itself fails. RECEIVED for review November 9, 1970. Accepted January 11, 1971. (3) C. Landault and G. Guiochon, CAromutogruphia, 1, 119, 277 ( 1968). (4) C. Vidal-Madjar, J. Ganansia, and G. Guiochon, “Gas Chromatography 1970,” N. Stock, Ed., The Institute of Petroleum, London, to be published.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 6, MAY 1971
807
