Paul J. Cowan' and James M. Sugihara University of Utah salt Lake City
A Gas Chromatography Demonstration Apparatus
chromatography is one of the most valuable methods available for the separation of mixtures. A lecture demonstration or a student experiment dealing with paper or column chromatography is readily accomplished. However, an extension to gas chromatography presents some difficulties. I n the work described herein, an inexpensive apparatus was constructed and shown to effect satisfactory separations of mixtures of several organic liquids. Detection of the components in the effluent stream was accomplished using a simplified version of the method described by Scott,%who measured changes in temperatures above a hydrogen flame by means of a thermocouple. I n this study a visual observation of changes in nature and height of the flame was found to permit a semiquantitative detection. A four-foot length of 6-mm glass tubing was bent into a U-shape with one leg about twice as long as the other. A glass tee was attached to the short end, and the vertical opening was closed with a rubber serum bottle cap. A second tee was attached to the horizontal opening and the resulting two openings connected to a manometer and the hydrogen source. A wad of glass wool was placed below the rubber cap to provide increased solid surface to facilitate evaporation of the sample. A heatiug tape was wrapped around this section of the apparatus to bring about rapid evaporation of the liquid sample. The heating tape may be extended to the U-tube, permitting chromatography at higher temperatures for mixtures of less volatile compounds. A short piece of l-mm capillary tube was connected to the long end of the U-tube. The U-tube was packed with Tide3 detergent powder, previously screened to remove - 100 mesh particles. the smallest particles were found to impede the rate of gas flow to the extent that the solid tended to be dislodged from the tube. Dinonyl phthalate on a fire brick support4was also used as the stationary phase. The flow rate of hydrogen was varied between 35 to 300 ml per minute. I n most experiments a rate of flow of about 100 ml per minute was found to be advantageous. This variable influenced the rate of passage of a given compound through the column but, within the limits applied, did not affect the degree of separation of the mixtures used. After hydrogen had flushed air from the system, the gas emitted through the capillary was Abstracted from the Master of Science Education Thesis of Paul J. Cowan, University of Utah, June, 1958. I Member of the Academic Year Institute, University of Utah, 1957-58. 'SCOTT,R. p. W., Ndure, 176, 793 (1955). A product of Practer and Gamble Co., Cincinnati, Ohio. ' A product of Central Scientific Co., Chicago, Illinois.
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Journal of Chemicol Education
SMALL CAPILLARY
n
SMALL PLASTIC BOTTLE WlTH
-+
LEAK HOLE
SAMPLE ENTRANCE
/ LIGHT OIL I N MANOMETER COLUMN FILLED WlTH PACKING
ignited. The sample (0.01 to 0.02 ml) was introduced through the rubber cap using a hypodermic syringe. The time of arrival of each of the components could be readily determined by a change in the characteristics of the hydrogen flame. The nearly colorless flame became luminous in the presence of organic compounds. The presence of halogenated substances was readily detected by attaching a coil of copper wire to the exit nozzle. A bright blue-green colored flame was obtained as described by Beilstein's test.s The apparatus was calibrated for several compounds, and changes in the flame characteristics were noted. The time of arrival, the time required for the flame to reach maximum height, the time of disappearance, and the maximum height of the flame were determined for each of a variety of organic liquids, for example, ethyl ether, acetone, carbon disulfide, chloroform, carbon tetrachloride, benzene, toluene, ethylbenzene, and the xylenes. Flame heights rose from about 0.5 mm t o as much as 8 mm depending upon the nature of the compound and the sample size. The duration of the luminous flame varied from about 15 seconds for ethyl ether to a little more than a minute for the xylenes but was again dependent upon the sample size. The flame reached its maximum height after approxi-
AND
SERENEE, R. L., F u s o ~R. , C., CURTIN, D. Y., "The Systematic Identification of Organic Compounds," 4th ed., John Wiley h Srms, Inc., New York, 1956, p. 60.
mately one-third of the total time duration, indicating a small degree of trailing. The plot of flame heights versus time gave curves from which areas under each of the humps were found to correspond to the sample size in a semiquantitative fashion. Different mixtures of compounds were found to be separable. The calibration dates were used to identify each of the components. Data (see Table 1) ,from a mixture of ethyl ether, carbon disulfide, carbon tetrachloride, and benzene gave a graph with four discrete humps with the order of appearance of the components in the order given. The complete separation of this mixture was effected using Tide detergent as the fixed phase, maintained at 60". A mixture of ethyl ether, acetone, 1,l-dichloroethane, carbon tetrachloride, and chloroform appeared in the order given from a column packed with dinonyl phthalate on a firebrick support a t a temperature of 110' (see Table 2). Separation was complete. With dinonyl phthalate as the stationary phase again a t a temperature of 110°, benzene, toluene, ethylbenzeue, and o-xylene were separable but not mxylene and p-xylene. The examples given below are merely representative of the types of separation possible in this simple illustration of gas chromatography.
Table 1.
Compound
A Sewration Usina Tide Deteraent Time of appearance (min) Start Max. End
Nature of flame
Ethyl ether 0.60 0.65 0.75 Bright yellow Carbon disul6de 0.85 0.90 1.10 Light-blue to lavender Benzene 1.65 1.78 1.96 Brieht vellow and srnokv tetrachloride and smoky Column length = 200 cm; temp = 60%; flow rate = 111 ml/ min: samde she = 0.01 ml.
Table 2.
A Separation Using Dinonyl Phthalate Time of appearance (-..., Start PEax. End U"",
Compound
Nature of flame
Ethyl ether Acetone 1,l-Dichloroethane Carbon tetrachloride Chloroform
0.94 1 .OO 1.12 Bright yellow 1.28 1.40 1.E. 1.82 1.90 2.05 Light-blue turning to yellow 2.46 2 . 60 3.04 Blue turning to yellow and smoky 3.55 3.70 4 . 3 0 Blue turning to yellow and smokv Column length = 165 cm; temp = 110°C; flowrace = 88.5mlI min; sample she =: 0.02 ml.
Volume 36, Number 5, May 1959
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