especially Fred Kohler, for excellent cooperation in the construction of the instrument. REFERENCES
(l),Condon, R. D., “The Design Considerations of a Gas Chromatography System Employpg High Efficiency Golay Columns, Perkin-Elmer Corp., Norwalk, Conn., 1959; ANAL. CHEhf. 31, 1717 (1959). (2) Corse, J., Dimick, K. P., “Flavor Research and Food Acceptance,’’ A. D . Little, ed., p. 302, Reinhold, New York, 1958. (3) DalNogare, S., Harden, J. C., ANAL. CHEM.31,1829 (1959). (4) Golay, M. J. E., “Gas Chromatog-
raphy 1958,” p. 36, Academic Press, New York, 1958. (5) Guild, L., Bingham, S., Aul, F., “Gas Chromatography 1958,” p. 226, Academic Press, New York, 1958. (6) Hardy, C. J., Pollard, F. H., J . Chromatog. 2, l(1959). (7) James, A. T., Martin, A. J. P., Bzochem. J. 50, 679 (1952). (8) Keulemans, A. I. M., “Gas Chromatography,” Reinhold, New York, 1957. (9) Lipsky, S. R., Lawdowne, R. A,, Lovelock, J. E., ANAL. CHEM.31, 852 (1959). (10) Lipsky, S. R., Lovelock, J. E. Landowne, R. A., J . A m , Chem. SOC.81, 1010 (1959). (11) Lovelock, J. E., Nature 182, 1663 (1958). (12) McWilliams, I. G., Dewar, R. A,,
“Gas Chromatography 1958,” D. H. Desty, ed., p. 142, Academic Press, Kew York, 1958. (13) Stross, F. H., “Gas Chromatography 1958,” D. H. Desty, ed., p. 186, Acsdemic Press, New York, 1958. (14) Sullivan, J. H., Walsh, J. T., Merritt, C. J., ANAL.CHEM.31, 1826 (1959). (15) Teranishi, R., Nimmo, C. C., Corse, J . ,Zbid., 32,896 (1960). RECEIVED for review November 27, 1959. Accepted May 2, 1960. Division of Analytical Chemistry, 137th Meeting, ACS, Cleveland, Ohio, April 1960. Use of a brand name does not imply that such products are endorsed by the U. S. Department of Agriculture or that they are recommended over the products of other firms.
Molten Salt Mixtures as Liquid Phases in Gas Chromatography WALTER W. HANNEMAN, CHARLES F. SPENCER, and JULIAN F. JOHNSON California Research Corp., Richmond, Calif.
b A new column for gas chromatography permits operation in the temperature range from 150’ to over 400’ C. The column packing is an inorganic salt eutectic on firebrick. A typical composition is a mixture of sodium, potassium, and lithium nitrates supported in a conventional manner on crushed insulating brick. The melting point of this eutectic is about 150” C. The upper limit of operation is determined by the thermal stability of the sample. The resolution of the column is relatively low compared to conventional organic packings. However, retention volumes are also low, permitting use of long columns. This paper describes the column packing material and presents tables showing the resolution on various types of organic compounds, particularly polyphenyls.
silicone’gum, and polyethylene. Liquid phases and instrumentation have been described (1-6, 8). The desirable properties of a high temperature liquid phase are thermal stability, low volatility at elevated temperatures, and sufficient resolving power to be useful. As considerable effort has not produced such an organic liquid, inorganic molten salt mixtures were tried and found to be very useful. The use of such materials for temperatures above 500” C. has been suggested by Phillips (9). Juvet and Wachi (’7) have reported partial separations of volatile transition metal chlorides on inorganic salt eutectics. However, no results on the use of molten salts to separate organic compounds appear to have been reported to date.
T
The gas chromatograph constructed in this laboratory was of conventional design. It had two stirred air thermostated ovens to permit operation of two columns in series. Temperatures were regulated by resistance actuated controllers and were uniform to +0.5” C. Detectors were of the thermal conductivity type using resistance wire elements. The use of two detectors was a departure from the conventional design. Schematically, the arrangement was preheater, injector block, Detector S o . 1, column, Detector N o . 2. Detectors Kos. 1 and 2 were carefully matched. By switching the bridge and recorder
EXPERIMENTAL
nE UTILITYof
gas chromatography for separating mixtures of high boiling organic compounds has been limited by the lack of a completely satisfactory stationary liquid phase. Problems encountered include the loss of liquid phase by vaporization and by decomposition. The loss by vaporization interferes with trapping portions of the sample for subsequent examination by ultraviolet, infrared, or highmass mass spectrometry. Liquid phases that have been used a t temperatures of 300’ C. and higher arp silicone greases, Apiezon greases,
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ANALYTICAL CHEMISTRY
circuit from No. 2 to No. 1 while simultaneously blocking the exit and removing the septum in the injector block, it was possible to provide backflushing utilizing appropriate plumbing without the use of valves. This was necessary because no suitable packing-free valve that would operate a t these temperatures could be found. The gas chromatographic columns used in this investigation were 50 feet in length. Although the original column w&s made from ‘/r-inch outer diameter copper tubing, with constant use at high temperature the copper tubing, rather than the column packing, was the first to fail. Subsequent columns have been made from ‘/d-inch outer diameter stainless steel tubing. One column packing was a eutectic mixture composed of sodium, potassium, and lithium nitrates (18.2:54.5:27.3 weight %). This salt mixture was dissolved in water and GC-22 firebrick, 42- to 60-mesh size, was added. The amount of salt mixture was 28.6 weight The mixture was evaporated to dryness and the column packed in the usual manner. Before any analysis could be run, it was necessary to bake out any retained water by heating the column a t a temperature above 300’ C. until the base line on the recorder was stable. This column could be operated in the range of 150’ (the melting point of the salt eutectic) to 400’ C. Helium mas used a t a flow rate of 35 ml. per minute as measured a t the column exit with a sqap bubble flowmeter. Samples ranging from 1 to 150 pl, were used. To determine the conditions for optimum resolution, the H E T P (height
x,
I
I
di
2 -
E
'1 t
-~ Degrees Centigrade 250 300 350 400 3.4 1 0 0 4 0 61 2 12 4 4 3 1 5
e/
Biphenyl m-Terphenyl m-Quaterphenyl l,OOOa 121 34 m-Quinquephenyl 12,500" 1,3OOa 200 4
4 t
3L 0
Table I. Retention Times in Minutes of Polyphenyl Compounds
I
2
1
4
5
8
7
8
S
I
O
I
I
6 9
Extrapolated values.
GAS VELOCITY, ml./tec
a
5
1 1
10
LI
10
10
MINUTiS
Figure 2. phenyls
Separation
of
m-poly-
Column liquid, salt eutectic; temperature, 400' C.; helium flow, 35 ml./min.
Plots of the log of the retention time us. the number of carbon atoms for the
normal paraffins a t 300' (2. and covering the range of CIS to C28 mere made. .4 straight line relationship, typical of gas-liquid chromatographic measurements, was observed. The retention times of polyphenyl compounds measured a t column temperatures from 250' to 400' C. are listed in Table 1. Figure 2 is a n illustration of a chromatogram :it 400' C. and shows that separation of the polypheryl compounds on the basis of the number of rings can bc effected. These fractions can thcn b(, collected and, upon rerunning under optimum conditions, good resolution can he obtained. Figure 3 shows a chromatogram of a mixture of phenyl-m-terphenyls run a t 340' C. Times from the air peak are given as abscissa. The general utility of such a stationary liquid phase has been demonstrated by measurements on several compounds of diverse types. These results are listed in Table 11. The following compound types are included : pyridines, quinolines, sulfides. aromatic ethers, aliphatic aromatic ethers, furans, ketones, isothiocyanates, amines, thiazoles, terpenoid compounds, olcfinic, acetylinic, paraffinic, and polyaromatic hydrocarbons. DISCUSSION
Gas chromatographic columns using molten inorganic salts as the stationary liquid phase apparently behave in the same manner as columns with conven-
Y
LO
4.
MINUTES
of
isomeric
Temperature, 340' C.; other Conditions same as Figure 2
Figure 1 . Influence of helium velocity on column efficiency
RESULTS
20
Figure 3. Separation phenyl-m-terphenyls
i
equivalent to a theoretical plate) was dctermined as a function of the gas velocity. Typiral results are shown in Figure 1. The minimum corresponds very closely to that determined for columns containing organic stationary liquid phases-eg., silicone and asphalt. All measurements reported were carried out at flow rates of 35 ml. per minute.
0
25.4
tional organic liquid phases. This seems to fit the observed variation of HETP with flow rate, the linear plots of log retention time 1's. carbon number
Table
II.
for homologous series, and the syminetrical peaks. I n any case, useful separations are obtained. Further, it is possible to trap uncontaminated fractions for subsequent identification and analyses by other analytical methods. Small samples are required for optimum resolution. However, the sample size, about 1 pl., is such that it can be handled (mil?- with thermal conductivity detectors. This gives the advantage of linear response and does away with the elaborate calibrations frequentlrequired by other tj.pes of detectors. The low solubility also results in relatively short retention times. This makes opwation at lower temperatures
Retention Times in Minutes of Materials Studied
150 5,7 10.5 13.5 2.0 6.1
160 4.3 7.8 9.5 1.5 5 2
2,3-Lutidine 2,bLutidine 2,j-Lutidine 2,6-Lutidine 2,4,6-Collidine Qujnoline Quinaldine 2,6-Dimsthylquinoline 1-Chloronaphthalene 1-Bromonaphthalene 1-Methylnaphthalene 12.8 2-Methylnaphthalene 13.3 1-Methoxynaphthalene 40.8 27.2 1-(.Y,S-Diethylamino j-naphthalene Phenyl sulfide Benzyl sulfide Dibenzothiophene Diphenyl ether 20.3 Benzyl phenyl ether Dibenzyl ether Dibenzofuran trans-Stil bene Diphen yla eetglene p-Dicyclohexylbenzene 1,6-Diphenylhexatriene 1,4-Diphenyl-1,3-butadiene Triphenylethylene 2-hlethyldiphenylmethane
4-Methyldiphenylmethane 2-Ethyldiphenylmethane 4-Ethyldiphenylmethane Acetophenone Phenyl isothiocyanate S,A'-Diniethylbenzylamille
1-Methylmercaptohenzot hiazole Cineole
--
31.0
10.0
6.0
7.8 4 5
5,l
3.8
Degrees Centigrade 175 200 225 250 275 300 2.8 5.0 6.1 0.9 4.0 19.5 8 7 3 . 3 10.1 5 . 0 2 . 3 12.0 6 . 6 3 . 1 13 9 6 7 2 . 9 23 8 11.6 4 9 0.5 8 . 2 4.0 8.0 3.7 17,6 6.1 3.4 1.8 7,2 3.6 1.8 52.7 13.0 2.9 33 0 8 4 2.1 12 8 6.3 17.8 8 . 4 3 . 5 30.6 13.7 6 1 23.9 11.7 5 . 2 58,5 8 . 5 4 2 2.2 38 0 10.5 5 . 0 1 1 4 3.,5 2 . 4 13.3 5 . 2 1.8 33.6 15.2 6 . 8 23.4 11.6 5 . 4 11 9 5,o 2.3 12.6 5 . 3 2 3 16 4 6 6 2 . 9 18.6 7 . 4 3 3 13 7 4.2 5 0 3 3 47 2 25.0 6.5 2.5
VOL. 32, NO. I I , OCTOBER 1960
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both practical and desirable. Use of molten salt stationary phases makes possible separations of high boiling compounds limited only by their thermal stability. LITERATURE CITED
(1) Adlard, E. R., Whitman, B. T., “Gas Chromatography,” D. H. Desty, ed., p. 351, Butterworths, London, 1958. ( 2 ) Cropper, F. R., Heywqpd, A., “Vapor Phase Chromatography, D. H. Desty,
ed., p. 316, Butteraorths, London, 1957. (3) Davies, A. J., Johnson, J. K., Ibid., p. 185. (4) Felton, H. R., “Gas Chromatography,” V. J. Coates, I. S. Fagerson, and H. J. Noebels, eds., p. 131, Academic Press, Sew York, 1958. (5) Guild, L., Bingham, S., Aul, F., “Gas Chromatography,” D. H. Desty, ed., p. 226, Butterworths, London, 1958. (6) Hawkes, J. C., “Vapor Phase Chromatography,” D. H. Desty, ed., p. 266, Butterworths, London, 1957.
( 7 ) Juvet, R. S., Wachi, F. M., ANAL. CHEM.32.290 11960).
Xoebels, eds., p, 51, y4cademic Press, New York, 1958. RECEIVEDfor review March 17, 1960. Accepted June 13, 1960. Division of Analytical Chemistry, 137th Meeting, ACS, Cleveland, Ohio, April 1960. Work conducted in part under Atomic Energy Commission Contract .4T(11-1)-174.
Analysis of Sulfonic Acids and Salts by Gas Chromatography of Volatile Derivatives J. J. KIRKLAND Industrial and Biochemicals Department, Experimental Station, E. I. du font de Nemours 8, Co., lnc., Wilmingfon, Del.
b Gas chromatography has proved to b e extremely valuable for analyzing a wide range of nonvolatile sulfonic acids and salts. Following quantitative conversion to volatile derivatives, complex mixtures of difficultly analyzed homologs and isomers can b e separated by conventional techniques. Aliphatic, aromatic, and alkyl aryl sulfonic acids and their salts are conveniently converted to corresponding sulfonyl chlorides by reaction with thionyl chloride or phosgene in the presence of a catalyst. Free sulfonic acids, including hydrates, may also b e similarly analyzed as methyl ester derivatives after esterification with diazomethane. Procedures are given for carrying out the conversion reactions, and illustrations of the analysis of typical mixtures are shown.
G
because O f its exceptional selectivity, has been used for the analysis of a wide range of volatile rnaterials containing close-boiling homologs and isomers. Nonvolatile, or lowvolatility compound., have also been analyzed, following conversion to more volatile derivatives (1, 5, 7 ) . Kew methods are herein proposed for analyzing complex mixtures of nonvolatile sulfonic acids and salts by gas chromatography of volatile derivatives. The suggested techniques are faster, more convenient, and more precise than liquid and paper chromatography approaches, and have the advantages of higher selectivity and accuracy over possiblt infrared spectrophotometric procedures. Aliphatic, aromatic, and alkyl aryl sulfonic acids and salts may be conAS CHROMATOGRAPHY,
1388
ANALYTICAL CHEMISTRY
verted in very high yields to corresponding sulfonyl chlorides by reaction with thionyl chloride or phosgene in the presence of certain formamide derivatives (g-4). This procedure has been found convenient for the quantitative preparation of sulfonyl chloride derivatives which can be analyzed by conventional gas chromatography techniques. Esterification reactions have previously been employed for the gas chromatographic separation of carboxylic acids; however, sulfonic acids have not been handled in this manner. I n this study, methods have been developed for analyzing sulfonic acids using this principle. I t was found that diazomethane is a convenient reagent for the esterification, but that chromatographic separations must be carried out a t reduced pressure to prevent sample decomposition. The esterification approach is preferred for the analysis of free sulfonic acids containing other functional groups which react with thionyl chloride or phosgene, or with compounds which isomerize or decompose during the vigorous reaction with these reagents.
stirred air bath was maintained constant ( h 0 . l o C.), with a Thermotrol proportional controller (Model 1050, Hallikainen Instruments, Berkeley, Calif.). T o permit independent heating, the vaporizer block of the instrument was equipped with a small metal contact heater powered by a Variac. Programmed temperature separations were carried out on a Model 202-B gas chromatograph (F & 11 Scientific Corp., 1202 Arnold Ave., S e w Castle County Air Base, h’ew Castle, Del.). This unit was equipped with a 1-mv. Minneapolis-Honeywell Brown recorder. Reduced-pressure separations of sulfonic esters were made on an F Br: M Scientific Corp. Model 17-A gas chromatograph. The column outlet was connected in succession to a cold trap, 5-liter surge tank, Cartesian manostat, and vacuum pump. The manostat regulated the outlet pressure, which was measured with a mercury manometer. Carrier gas was delivered into the column a t the desired flon- rate by means of a fine control needle valve placed between the regulator and the column inlet. Only a very slight positive pressure on the inlet of the needle valve was needed to attain the desired flow rate, I n front of the valve, a rotameter was inserted to estimate the carrier gas flow through EXPERIMENTAL the column. A mercury manometer was connected in parallel n i t h the Apparatus and Reagents. G a s CHROMATOGRAPHIC IXSTRUMENTS. A4 column input t o measure the input pressure. The detector bridge output Perkin-Elmer Model 154-A Vapor was monitored with a 1-niv. 1IinneFractometer, equipped with a 1-mv. apolis-Honeyr-iell Brown recorder. Leeds & Korthrup Speedomax Type Dry helium was used as the carrier G recorder, was used for isothermal gas in all operations. Helium floiv rates separations of sulfonyl chlorides. T h e were measured with a soap film meter, instrument was modified t o permit except in the reduced pressure separaoperation up t o 225’ C. by t h e additions. tion of sufficient insulation a n d heatCOLUMN^. For the isothermal sepaing capacity. Thermistors of 8000rations of sulfonyl chloride derivatives, ohm resistance mere installed to provide a 2-foot silicon grease column was adequate sensitivity a t the higher temprepared b y coating 40- to 50-mesh peratures. The temperature of the
