Apparatus for Rapid Degassing of Liquids. Part 111 Rubin Battino, Mark Banzhof, Michael Bogan, and Emmerich Wilhelm Department of Chemistry, Wright State Unicersity, Dayton, Ohio 45431
DEGASSING OF LIQUIDS is important for many procedures. We have previously reported ( I , 2) (Parts I and 11, respectively) on two apparatuses for the rapid degassing of liquids. The apparatus in I used an all glass pumping system to circulate the liquid, and the apparatus in I1 used rotating Kel-F paddles in a horizontal cylinder. Although both I and I1 work quite well, they are mechanically complicated and difficult to fabricate. Recently Bell et al. (3), reported on an apparatus for degassing liquids by vacuum sublimation. Their procedure is slow (1 to 2 hours for 40 cm3) and can only handle small (ca. 40 cm3) samples. The apparatus described in this paper is easy to fabricate, very easy t o use, capable of handling liquid samples of the order of 500 cm3, and degasses rapidly. We find it quite superior to I and I1 jn all aspects. ERLENMEYER
APPARATUS AND PROCEDURE
The apparatus is shown in Figure 1 and is drawn to scale as indicated. The apparatus was fabricated from a standard 2-liter heavy wall filtering flask with tubulation. The stopcocks used are the Fischer and Porter quick-opening needle (4 mm) valves with Teflon (Du Pont) stems. The stopcocks hold vacuum to better than 1 micron and provide grease-free
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(1) R. Battino and F. D. Evans, ANAL.CHEM., 38,1627 (1966). (2) R. Battino, F. D. Evans, and M. Bogan, Aitnl. Chirn. Acta, 43, 518 (1968). (3) T. N. Bell, E. L. Cussler, K. R. Harris, C. N. Pepela, and P. J. Dunlop, J . Pliys. Chem., 72,4693 (1968).
Figure 2. Degassing apparatus made from a 3-liter Erlenmeyer flask
II VAC 2 LITER FILTER FLASK
Figure 1. Degassing apparatus made from a 2-liter filter flask 806
ANALYTICAL CHEMISTRY, VOL. 43, NO. 6, MAY 1971
connections. The 35/25 O-ring joint provided a greasefree vacuum tight closure for introducing the stirring bar and the liquids. A 20 cm long condenser was added at the tubulation end of the filter flask and was used to minimize loss of liquid to the liquid nitrogen trap. A thermocouple gauge (calibrated against a McLeod gauge) served as a pressure indicator. The sample size was 500 cm3 for all trials. This resulted in a ca. 4 cm deep layer of liquid in the flask. After adding the liquid, the stirrer is turned on and the speed of stirring is increased slowly. We found that a 3 in. long octagonal cross-section stirring bar with a spinning ring in the middle was most efficient. With good stirring action, the liquid is splashed up against the walls of the flask and a strong vortex is formed around the bar. Two different procedures were followed depending on whether the liquid was volatile or nonvolatile. For a volatile liquid with stopcocks S1, S2, and S3 closed, the system is pumped down t o its base pressure (normally 5-10 p ) , using a rotary forepump and a mercury diffusion pump. Stopcock S4 is closed and S3 opened for 2-3 seconds. After waiting 1 minute for the vapor to freeze out, the pressure is read and stopcock S4 is opened to pump down the trap section. When the base pressure is reached, the procedure of expanding from the filter flask to the trap section is repeated. When the pressure reaches the base pressure of the system for two successive trials, the liquid is considered degassed. This procedure assures that the pressure increment above base pressure is due only to residual permanent gases.
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.
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