Roberl Silberman
A Simple Gas-Liquid
State University of N e w York College of Cortland Cortiond, N e w York 13045
Chromatography Device
I n the past several years, several very simple devices have been designed or suggested for demonstrating the principle of gas chromatography.' The difficulty seems to be in designing a simple, inexpensive, detection system which can be used to get quantitative or semi-quarrtitative results. An early report of the analysis of cracking fractions for ethane describes the use of carbon dioxide as the carrier gas which is absorbed in sodium hydroxide.? This principle can easily be modified for classroom use. The necessary equipment consists of a standard gas chromatography column, a few Swagelocks, a rubber septum, a number of 8-mm glass tubes, rubber tubing,
8
MM
TUBES
)AS INLET
SiLlCOliE RUBBER SEPTUF: Diagram of devise for gas-liquid chromatography.
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lournal of Chemical Education
and sodium hydroxide solution. The set-up of the apparatus is illustrated in the figure. The carrier gas is carbon dioxide from a commercial tank a t a pressure of 10-20 psi. The sample is injected through the septum onto the column using a hypodermic syringe. For demonstration a gas or a very low boiling liquid, such as ethyl chloride, works well. A mixture of ethyl chloride and air can be separated at room temperature on a silicone oil column with the end attached to a rubber tuhe with a bent glass tuhe that can be hooked under each collector. The collection tubes are made of 8-mm glass tubing sealed a t one end and filled with concentrated sodium hydroxide solution. The effluent gases are bubbled into the collection tubes, the CO, is absorbed, and the sample gas then displaces the hydroxide solution. Measurement of the displaced volume allows one to determine quantitatively the amount of gas present. When sodium hydroxide is no longer displaced, the hooked glass tuhe is moved. In this way a several component mixture can be analyzed. If a commercial cylinder of carbon dioxide is used which contains air as an impurity, a blank must he run by bubbling the carbon dioxide into a collection tube and measuring the displacement of solution as a function of time. If the procedure is used as a demonstration, a dark colored indicator such as thymol blue can be added to the sodium hydroxide solution. The experiment is a simple one and does allow a student to do a semi-quantitative experiment. COWAN, P. J., AND SUGIAERA, J. M., J. CKEM.EDUC.,36, 246 (1959). HERBENER, R. E., J. CHEM.EDUC.,41, 162 (1964) H., J. CKEM.EUUC.,43,660 (1966). LOWELL, S., AND MALAMUD, 2 DM, NOG-, S., AND JUVET,R. S., "Gm Liquid Chromatography,"Intencience, (a division of John Wiley & Sons, Inc.), New York, 1962, p. 229.
