time of 3 seconds before the needle was extracted gave satisfactory results. Peak height measurements were more difficult to repeat quantitatively but were measured more easily for compounds having low retention times. Peak areas were affected less easily by slight instrumental variations. Careful techniques, including close control of temperature, helium gas flow rate, and injection, and cleanliness of the thermoconductivity cell filaments gave a precision of 1 0 . 0 2 bmole. If necessary, the use of an internal standard would help compensate for slight variations in technique and instrumental conditions. ACKNOWLEDGMENT
Most of the work on this study was
supported by a U. S. Public Health Service Grant No. RG-5575. LITERATURE CITED
(1) Ambrose, D., Keulemans, A. I. M., Purnell, J. H., ANAL. CHEM.30, 1582 (1958). (2) Ambrose, D., zurnell, J. H., “Gas Chromatography, D. E. Desty, ed. p. 369, Academic Press, New York, 19.58. (3) Desty, D. H., Swanton, W. T., J . Phys. Chem. 65, 766 (1961). ( 4 ) Green, S. W., “Vapor Phase Chro-
matography,” D. E. Desty, ed. p. 388, Academic Press, New York, 1957. ( 5 ) Hardy, C. J., J . Chromatog. 2, 490 (1961). (6) Harrison, G. F., “Vapor Phase Chromatography,” D. E. Desty, ed. p. 332, Academic Press, New York, 1957. (7) Haslam, J., Jeffs, -4.R., Analyst 83, 455 (1958). (8) Hoare, M. R., Purnell, J. H., Trans. Faraday SOC.52, 222 (1956).
(9) Jordan, J. E., “Vapor Pressure of Organic Compounds,” Interscience, New York, 1954. (10) .Littlewood, 8.B., Phillips, C. S. G., Price, D. T., J . Chem. Soc. 1955, 1480. (11) Pollard, F. H., Hardy, C. J., Anal. Chim. Acta 16, 135 (1957). (12) Porter, P. E., Deal, C. H., Stross, F. H., J . Am. Chem. Soc. 78, 2999 (1956). (13) Purnell, J. H., Spencer, M. S., h’ature 175, 988 (1955). (14) Rossini, F. D., Wagman, D. D., Evans, W. H., Levine, S., Jaffe, I., “Selected Values of Chemical Thermodynamic Properties,” National Bureau of Standards Circular No. 500, Washington, D. C., 1952. (15) Urone, P., Smith, J. E., Am. Ind. Hyg. Assoc. J . 22,36 (1961). (16) Warren, G. W , Priestley, J. J., Jr., Haskin, J. F., Yarborough, V. A., ANAL. CHEW.31, 1013 (1959). RECEIVED for review November 16, 1961. Accepted January 22, 1962.
Identification of Alcohol Peaks in Gas Chromatography by a Nonaqueous Extraction Technique ROBERT SUFFIS and DONALD E. DEAN Shulton, Inc., Clifton, N. 1. b A technique for the identification of the gas chromatographic peaks due to alcohols has been developed. The method is based on the qualitative separation of the alcohols from other components by a nonaqueous extraction. The peaks removed by the extraction procedure are identified by gas chromatography. Further characterization may be obtained by spectrophotometric methods.
T
of the separated components in gas chromatography has been the subject of considerable study. The most coinnionly utilized techniques involve the isolation of the compounds by solvent trapping or freezing-out. Further analysis is performed by infrared spectrophotometry (1) or mass spectrometry ( 3 ) . Another technique involves the application of functional group identification reactions to the column effluent ( 5 ) . These methods have proved very useful, but they have certain limitations. If very small samples are used, resolution is poor; when destructive detection methods are used, i t may be difficult to use this type of approach. A misture may be analyzed by applying class reactions and then running the gas chromatograms before and after the reaction (4). The disappearance of certain peaks mill identify the functional 480
HE IDESTIFICATIOS
0
ANALYTICAL CHEMISTRY
group of those compounds. This information together \\ ith retention time data nil1 often lead to a definite identification. The identification of alcohols by this technique, known as separation analysis, is the subject of this paper. The method depends on the use of a nonaqueous estraction technique for the qualitative separation of alcohols from other organic compounds. il carbon tetrachloride solution of the misture is extracted with propylene glycol. Alcohols are quite soluble in the propylene glycol layer, whereas aldehydes, ketones, hydrocarbons, and esters are considerably more soluble in carbon tetrachloride. The relative decrease of any peak in the chromatogram of the carbon tetrachloride layer identifies that component as an alcohol. Acids, phenols, and amines are also soluble in propylene glycol. Hon ever, they may be evtracted and identified by aqueous acid or alkali extraction before the nonaqueous extraction. Prior methods for the separation analysis of alcohols involve reaction of these components IT ith benzoyl chloride or 2,4-dinitrobenzoyl chloride ( 2 ) . Our method has the advantage of not introducing any reagents and not converting the alcohols to new compounds. This makes it possible for the alcohols to be separated and identified by infrared or ultraviolet spectrophotometry. The separated layers may be ana-
lyzed directly by ultraviolet spectrophotometry after suitable dilutions. For infrared spectrophotometry, the layers can be extracted with a suitable infrared solvent after water is added to remove the propylene glycol. K h e n equal volumes of propylene glycol and carbon tetrachloride are shaken in a separatory funnel, two layers form. The lower layer is carbon tetrachloride containing 0.1% propylene glycol; the upper layer is propylene glycol with 15% carbon tetrachloride. Ethylene glycol, nitromethane, or acetonitrile may also be used as the polar liquid. Cyclohexane, petroleum ether, or carbon disulfide may be substituted for carbon tetrachloride. APPARATUS
Gas chromatograph, Perkin-Elmer Model 154C Vapor Fractometer a i t h helium as the carrier gas. Infrared spectrophotometry, PerkinElmer Model 21 infrared spectrophotometer. PROCEDURE
Extraction Procedure. A 2-gram sample of the pure compound or miuture is dissolved in 25 ml. of carbon tetrachloride. This solution is placed in a separatory funnel, and 25 ml. of propylene glycol are added. The separatory funnel is shaken thoroughly. The tn-o layers are separated, and
Table 1. Distribution Ratios between Carbon Tetrachloride and Propylene Glycol for Various Organic Compounds
Carbon ProTetra- pylene chloride Glycol Layer, Layer, Alcohols Ethyl alcohol Isopropyl alcohol %-Butyl alcohol Isoamyl alcohol n-Hexyl alcohol n-Octanol Benzyl alcohol Phenylethyl alcohol
TIME, MINUTES
Figure 1. Chromatogram of geraniol mixture
crude
a n appropriate size sample of each layer is r u n on the gas chromatograph. Preparation for Spectrophotometry. The carbon tetrachloride layer is extracted tnice with equal volumes of water. T h e carbon tetrachloride layer is dried over anhydrous sodium sulfate. An equal amount of water is added t o the propylene glycol layer. This layer is extracted twice with carbon tetrachloride or carbon disulfide. The lower layer is n ashed twice with water and dried over anhydrous sodium sulfate. RESULTS AND DISCUSSION
The distribution coefficients for a representative group of organic conipounds were determined (Table I). I n addition, we also determined the dis-
7
6
5
4
3
2
1
0
TIME, MINUTES
Figure 2. First carbon tetrachloride extract of crude geraniol mixture
Hydrocarbons %-Hexane n-Heptane Isooctane Benzene Toluene Aldehydes and Ketones a-Butyraldehyde n-Hexylaldeh yde Benzaldehyde .4cetone 2-Butanone 2-Heptanone Esters Ethyl acetate Butyl acetate Hexyl acetate Ethyl butyrate Benzyl acetate
%
74
12
88
11
17 20
89
83
32
80 76 68 94 89
93
7 4
91
9 7
74 89 93
26
24 6 11
96 94 93
64
77 84 87
89 94
86 91
6
L
11 7
0
36 23
16
Figure 3. Carbon tetrachloride layer of crude geraniol after two extractions with propylene glycol
13
11 6
14 9
tribution coefficients for 18 compounds containing a terpene skeleton. These data are summarized in Table 11. All the preceding data were determined by gas chromatographic analysis of the equilibrium phases. I n all cases there is a considerable difference between the behavior of alcohols and that of esters, aldehydes, ketones, and hydrocarbons. Although the separations are not quantitative, the distribution differences are great enough for qualitative identification. Any component that is more than 50% soluble in the propylene glycol layer may be identified as an alcohol. The method n a s applied to the analysis of tlvo natural products. X crude milture of geraniol and citronellol containing other impurities and a sample of geranium oil were run through the extraction technique The changes in composition were follo~~-edby gas chromatography. Figure 1 s h o w the chromatogram of the crude geraniol mixture. These chromatograms nere run using a 6 foot by inch aluminum column packed with 2,5% by w i g h t Carbon-ax 1640 on 60- to 100-mesh Chromosorb-K. The column temperature was 175" C. The helium flow rate v a s 60 cc per minute. Components 5 and 7 nere tentatively identified as citronellol and geraniol, respectively. If component 6 mere a n alcohol, n e could, on the basis
of retention time data, identify it a s nerol. If it were not a n alcohol, it wpuld be geranyl acetate which has the same retention time as this impurity. The sample was extracted; the chromatogram of the carbon tetrachloride layer is shown in Figure 2. The citronellol and geraniol have decreased greatly relative to the other peaks, particularly that of component 6. The carbon tetrachloride layer was extracted again with propylene glycol.
3
7
6
5
4
3
2
l
i
,
I
1
0
TIME, MINUTES
Figure 4. First propylene glycol layer of crude geraniol mixture VOL. 34, NO. 4, APRIL 1962
481
in
T
Table 11. Distribution Ratios between Carbon Tetrachloride and Propylene Glycol for Essential Oil Ingredients
Carbon ProTetra- pylene chloride Glycol Layer, Layer,
16 12 TIME, MINUTES
8
20
24
Figure 5. nium oil
Chromatogram of
4
0
gera-
.
Figure 3 shows the chromatogram of the second carbon tetrachloride extract. Peaks 5 and 7 show a further decrease confirming that these components are citronellol and geraniol, respectively. Peak 6, which was originally only a small impurity, is present in a higher concentration in the second extract than either geraniol or citronellol. Figure 4 shows the chromatogram of the propylene glycol layer. The two large peaks in this layer are citronellol and geraniol. All other components are either missing completely or are considerably reduced. This definitely establishes that component 6 is not a n alcohol. On that basis, this component was identified as geranyl acetate. This method also shows that components 1 to 4 are not alcohols.
TIME, MINUTES
Figure 6. First carbon tetrachloride extract of crude geraniol mixture
482
ANALYTICAL CHEMISTRY
Terpene Hydrocarbons p-Cymene Limonene Pinene Terpene Alcohols Linalool Geraniol Terpineol Isopulegol Menthol Borneol Terpene Aldehydes and Ketones Citral Camphor Menthone Carvone Fenchone Ionone Terpene Esters Linalyl acetate Geranyl formate Geranyl acetate
%
70
97 94 94
3 6
46 33
54
38 44 36 48
6 67 62
56 65 53
98 89 87 89 88 91
2 11 13
99 91 96
1 9 4
11
12 9
This extraction technique was helpful in identifying the alcohol components in geranium oil. These chromatograms were run using a 12 foot by 1/4 inch aluminum column containing 287, by
i
0
Figure 7. Carbon tetrachloride layer of geranium oil after two extractions with propylene glycol
Feight DC-550 silicone oil on 60 to 100 mesh Chromosorb-W. The temperature was 150" C. The helium flow rate was 35 cc. per minute. Figure 5 shows the chromatogram of geranium oil. The sample was extracted, and the car-
15
1
2
3
4
5
6 7 .8 9 IO I I WAVELENGTH, MICRONS
12
13
14
I
2
3
4
5
6 7 8 9 IO II WAVELENGTH, MICRONS
12
13
1415
Figure 8.
Infrared spectra of geranium oil extracts Top-Carbon tetrachloride layer Bottom-Propylene glycol layer
bon tetrachloride layer is shonn in Figure 6. Peaks 5, 9, and 10 decreased. On closer observation, it can be seen that peak 10 has shown a smaller decrease than either peak 5 or peak 9. The peak heights of components 9 and 10 are reversed after extraction. The carbon tetrachloride layer mas extracted once more n i t h propylene glycol. Figure 7 shoii s the chromatogram of the second carbon tetrachloride eLtract. Peaks 5 and 9 have decreased greatly and are almost absent. Removing most of component 5 has shown the presence of a minor component, which was not resolved in the original chromatogram. Peak 10 shows only a very small decrease after the second extraction. This fact indicates that peak 10 is actually composed of more than one component, one of mhich must be an alcohol. The major portion of this compound was removed in the first extraction. The other component of peak 10 has been identified as geranyl formate by its retention time. To establish the identity of the three alcohols, the infrared spectra of both the layers of the initial extraction mere run and are shown in Figure 8 To find out
nliich bands in the spectrum are due to alcohols, one chooses those bands that are stronger in the propylene glycol layer. These bands appear a t 2.90, 9.00, 9.45, and 10.05 microns. The band a t 9.00 microns is due to linalool. The band a t 9.45 microns is due to citronellol, and a t 10.05 microns, the band is assigned to geraniol. The bands a t 9.75, 5.82, 7-95, 8.15, 8.55, and 11.25 microns appear much stronger in the carbon tetrachloride layer. These bands must be due to esters, ketones, or terpenes. The band a t 5.75 microns has been assigned to the esters, and the one a t 5.85 microns to menthones. The bands a t 7.95 and 8.15 microns are assigned to citronellyl acetate and geranyl acetate, respectively. The band a t 8.55 microns is due to citronellyl and geranyl formates. The band a t 11.25 microns is due to terpenes. The infrared spectra of the extraction layers enable one to determine which bands in the original spectrum are due to alcohols and which are not. If there is doubt concerning any band because of almost equal intensity in both layers, this can be resolved by looking a t the spectra of further eutractions. The infrared
spectra have confirmed the identity of peaks 5 , 9, and 10 as linalool, citronellol, and geraniol, respectively. This extraction technique has been used for the rapid identification of alcohols in the chromatograms of complex mixtures. This technique can be used to complement the data from the isolation of components separated by gas chromatography. If further identification is necessary, the infrared or ultraviolet spectra of the layers can be run. This information, coupled with retention time data, should lead to a positive identification of the alcohol peaks in gas chromatograms. LITERATURE CITED
(1) Anderson, D. M. W., Duncan, J. L., Chem. & Ind. (London) 1958, 1662. (2) Bayer, E., Koepfer, G., Reuther, K. H. 2. anal. Chem. 164, 1-10 (1958). (3) dohlke, R. S.,ANAL.CHEM.31, 535 (\ -19.59’). - - - I -
(4) Rowan, R., Ibid., 33,658-65 (1961). (5) Walsh, J. T., Merritt, C., Ibid., 32, 1378-81 (1960). RECEIVED for review October 19, 1961. Accepted February 5, 1962. Division of Analytical Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961.
Determination of Dissolved Gases in Aqueous Solutions by Gas Chromatog ra phy JOHN W. SWINNERTON, VICTOR J. LINNENBOM, and CONRAD H. CHEEK U. S. Naval Research laboratory, Washington, D. C.
b A gas chromatographic method has been developed for the determination of small amounts of dissolved gases in aqueous solutions. The equipment consists of an all-glass sample chamber in which the dissolved gases are stripped from solution b y an inert carrier gas, a four-way by-pass valve, a commercially available gas partitioner, and a 1-mv. recorder. Calibration for routine work is accomplished b y carrying out the determination on a sample of water saturated with pure gas a t a known temperature and pressure. At present, the method is capable of determining dissolved gas concentrations as low as 0.3 p.p.m. in 1 - to 2-ml. samples of solution.
T
HE APPLICATION of
gas chromatogw h y to the determination of small amounts of dissolved gases in solution offers several advantages not found in either manometry or mass spectrometry. The method is less time consuming and better suited for routine
analytical work, sample size can be kept small, the instrumentation is relatively simple, and no loss is esperienced in either precision or accuracy. Paglis (5) has employed this technique for the determination of dissolved oxygen in petroleum liquids; however, his procedure involves introduction of the entire sample onto the chromatographic columns, and thus requires a pre-column employing both a liquid partition agent and an activated charcoal adsorbent in order to separate the hydrocarbons from the oxygen. Elsey (1) has also used gas chromatography for the determination of dissolved oxygen in lubricating oil; his procedure differs from that of Paglis (5) in that a preliminary separation of dissolved gas from the liquid is effected by injection of the sample into a preheated glass chamber, thus eliminating the necessity of an extra chromatographic column to adsorb the hydrocarbons. I n the procedure described below, the essential feature is the use of a special sample chamber designed a t this
laboratory, in which the dissolved gases are stripped from solution by the carrier gas and carried directly into a conventional gas chromatograph for analysis. This method has been found effective for the determination of dissolved gases in concentrations as low as 0.3 p.p.m. in 1to 2-ml. samples of liquid. Originally developed for the determination of radiolytic gas yields in irradiated aqueous solutions, the method is also applicable for routine oceanographic and water pollution work, and for the determination of dissolved gases in nonaqueous solutions. EXPERIMENTAL
Apparatus. A Fisher gas partitioner Model 25 was used in this work. This instrument employs two chromatographic columns in series, each having its own detector (Figure 1). A variety of columns may be used. I n this work, Column No. 1 consisted of 30% H M P A (hexamethylphosphoramide) on 60- t o 80-mesh Columpak, 6 feet by 1/4 inch. Column No. 2 consisted of 60- to 80-mesh Columpak, 4 VOL. 34; NO. 4, APRIL 1962
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