P r.
=
R RII
=
s
=
=
=
SI, S P = t
=
T G
=
v
=
v,
=
7
=
p
u,
= =
m
=
T
=
=
Compression ratio, p i / p , Capillary tube radius or mean particle radius Ratio of zone to gas velocity R value of component I1 or last component Important dimensionless parameter, Equation 10 Dimensionless parameters, Equation 10 Analysis time Temperature Constant in Equation 20 Gas flow velocity a t a given point in the column Flow velocity at column inlet Viscosity coefficient for carrier Reduced inlet pressure, p i / p , Collision diameter of carrier gas molecules Collision diameter of solute molecules Standard deviation in time of peak width
@
=
n
=
Column constant characterizing the resistance to flow Integral expressions, Equation 21 LITERATURE CITED
(1) Ayers, B. O., Loyd, R. J., DeFord, D. D., ANAL.CHEM.33,986 (1961). (2) Baker, W. J., Second Symposium on Gas Chromatography, East Lansing, Mich., 1959. (3) Desty, D. H., Goldup, A., “Gas Chromatography, 1960,” p. 162, R. P. W. Scott,. ed.,. Butterworths, Washington. (4)Giddings, J. C., ANAL.CHEM.32, 1707 (1960). ( 5 j lbid., 33, 962 (1961). (6) Giddings, J. C., J . Chromatog. 5 , 46, 61 (1961). (7) Giddings, J. C., Nature 184, 357 (1959); 187, 1023 (1960). (8) Ibid., 191, 1291 (1961). (9) Giddings, J. C., Robison, R. A., unpublished data. (10) Giddings, J. C., Seager, S. L., Stucki, L. R., Stevart, G. H., ANAL.
CHEM.31, 1738 (1959); 32, 867 (1960). (11) Golay, M. J. E., “Gas Chromatography,” p. 36, D. H. Desty, ed., Butterworths, London, 1958. (12) Hirschfelder, J. O., Curtiss, C. F., Bird, R. B., “Molecular Theory of Gases and Liquids,”Chap. 8, Wiley, New York, 1954. (13) James, A. T., Martin, A. J. P., Biochem. J . 50, 679 (1952). (14) Kieselbach, R., ANAL.CHEW33, 806 (1961). (15) Knox, J. H., J . Chem. SOC.1961,433. (16) Purnell, J. H., Quinn, C. P., “GaS Chromatography, 1960,” R. P. W. Scott, ed., Butterworths, Washington, n. 184. r .
(17) .Scott, R. P. W., Hazeldean, G. S. F., Ibzd., p. 144. (18) Trautz, M., Muller, W.,Ann,. Physik 22, 353 (1938). RECEIVEDfor review July 31, 1961’ Accepted December 26, 1961. Work supported by the U. S. Atomic Energy Commission under Contract AT-( 11-1)748.
Determination of Sulfur in Organic Compounds by Gas Chromatography DONALD R. BEUERMAN’ and CLIFTON E. MELOAN Department of Chemistry, Kansas State University, Manhatfan, Kan.
b Sulfur in organic compounds can be determined by combusting the compounds at 850” C. in a stream of oxygen using a platinum catalyst. The water of combustion i s removed with calcium sulfate, and the sulfur dioxide and carbon dioxide are trapped at liquid nitrogen temperatures along with some oxygen. The sulfur dioxide i s separated from the carbon dioxide and oxygen by a dinonylphthalate column using helium as a carrier gas. The complete analysis requires about 20 minutes, and a relative error of less than 1% can be expected. The method has been satisfactory with sulfoxides, sulfones, thiones, sulfides, disulfides, and thioethers, but sulfates were not converted to sulfur dioxide quantitatively under these conditions. Compounds containing fluorine, chlorine, nitrogen, and oxygen, in addition to carbon and hydrogen, were tested and found not to interfere.
T
HERE ARE, at present, two predominant methods for determining the sulfur content of organic compounds-the Carius and Pregl methods with their many variations (10). The Carius method consists of combusting the organic compound in a sealed tube in the presence of nitric acid and an
alkali salt other than a sulfate. The sulfate formed is then determined either gravimetrically or titrimetrically. The Pregl method consists of combusting the compound in a combustion tube at 650” C. using platinum as a catalyst. The resulting oxides of sulfur are then converted into sulfuric acid by their reaction with hydrogen peroxide. If nitrogen or halogens are present, the sulfate must be precipitated as barium sulfate and determined b y gravimetric techniques. Both methods require several hours for completion. Other methods have been described in the literature, but most of them are adapted to specific types of analysis. Huffman (6) adapted Pregl’s method t o the simultaneous determination of carbon, hydrogen, and sulfur. H e trapped the sulfur on silver and subjected t h e silver sulfate formed to electrolysis. The sulfur in organic compounds has been hydrogenated to hydrogen sulfide and determined b y various techniques (9). Sulfur has been determined manometrically b y Hoagland (4). The Schoniger oxygen flask (7) can be used for the combustion of sulfur compound. The above methods either require considerable time for completion or else are limited in application b y interfering substances. A fast, widely applicable, reasonably accurate method for sulfur t h a t could be used over a
wide range of sample sizes, particularly small samples, was desired. The possibility of gas-liquid partition chromatography was examined because it should provide a means of separating interfering materials. Four questions had to be answered before this approach would be feasible. Could sulfur be combusted to SO, without forming SO3? Would mater react with the SO,; and if so, could this be eliminated? Could the SO, be efTectively trapped for a concentrating step? Could SOz be separated from the other possible gases in a reasonable time? Duswalt and Brandt (3) and Sundberg and Maresh (11) devcloped a method for determining carbon and hydrogen in organic compounds by utilizing the principles of gas chromatography, enabling a carbon-hydrogen determination to be completed in 20 minutes. Scott et al. ( 8 ) modified this technique for the determination of oxygen and nitrogen. hIaresh (6) adapted i t to the simultaneous determination of carbon, hydrogen, and nitrogen. This paper describes development of techniques using gas chromatography for the determination of sulfur in organic compounds.
1
Present address, Monsanto Chemical
Co., St. Louis, Mo.
VOL. 34, NO. 3, MARCH 1962
319
Figure 1 . A. B. C. D.
E. F. G. H. 1.
1. K. L.
M.
Experimental a p p a r a t u s
Cylinder of oxygen fitted with a two-stage pressure regulator and a V e e point needle valve Bubble counter U tube fllled with Ascarite, Anhydrone, and mineral oil Cork Pyrex combustion tube-Fisher No. 2 0 - 2 2 8 Platinum or porcelain sample b o a t A r e a o f the small movable heater of the combustion furnace 10% platinized asbestos Platinum contact stars Area o f the long heater of the combustion furnace Pregl absorption tube filled with calcium sulfate, using glass wool a t the ends Cold t r a p which contains two three-way stopcocks. There a r e 4 in. between stopcocks a t the top, 2.5 in. across the bottom. The cold t r a p is 8 inches d e e p and m a d e of 7-mm. borosilicate glass D e w a r flask filled with liquid nitrogen Vacuum-may b e a water aspirator as only 20 to 30 mm. o f H g is required to prevent Os from condensing EXPERIMENTAL
The apparatus used in this T?iork (Figure 1) consisted of a combustion train, a trapping system, and a gas chromatograph. The combustion train consisted of an oxygen source, furnace. combustion tube, and a drying cartridge. The source of oxygen vias a cylinder of oxygen prepared by the distillation of liquid air. This was equipped with a txo-stage pressure regulator and needle valve. The oxygen was passed through a bubble counter U tube into the side arm of the combustion tube. The U shaped absorption tube was filled Rith Ascarite and Anhydrone to ensure that the oxygen was free of carbon dioxide and water. The combustion furnace was a Sargent automatic microcombustion furnace capable of obtaining temperatures of 900' C. The combustion tube was of borosilicate glass with a side arm inlet. The drying cartridge was a Pregl tube filled with calcium sulfate. This cartridge was used to remove water
Table I. Relation between Combustion Temperature and Formation of SOa Per Cent Temperature, Transmittance "C. Trial 1 Trial 2 Blank 100.0 100.0 650 39.8 35.1 700 63.1 59.7 750 88.7 85.9 800 99.1 99.3 825 100.0 100.0 850 100.0 100.0
320
ANALYTICAL CHEMlSTRY
from the combustion gases to prevent its reaction with sulfur dioxide to form sulfurous acid. A11 of the gas lines mere constructed from l/la-inch stainless steel tubing, Type 304. They were connected to the glass joints by inserting them into a silicone rubber seal connected to the glassware with rubber tubing. The cold trap was constructed from 7-mm. glass tubing. Silicone stopcock grease m s used very sparingly as a stopcock lubricant. The stopcocks nere held in place by Todd tension clips. These were necessary to prevent loss of material from the trap due to the increase in pressure upon vaporization of the trapped sample. The trap 11-as immersed in a 1-quart Dewar flask filled with liquid nitrogen. The gas chromatograph was of our own construction employing thermistors for a detector and a Sargent SR recorder. Helium nas used as the carrier gas. X 307, dinonylphthalate column, 20 feet long, operating a t 92" C. was used although a 10-foot column could be used. Quantitative Combustion to Sulfur Dioxide. A quantitative conversion to SO2 is required for the success of this determination so a simple experiment was performed to determine the combustion temperature beyond T i hich a n insignificant amount of SOa would be formed. Phenyl sulfoxide mas combusted a t different temperatures in a combustion tube packed with platinum asbestos and platinum stars. Oxygen was fed into the tube at a rate of 6 ml. per minute. The combustion gases were bubbled through
25 nil. of 1.011 BaC12. The BaCll was made acidic with HC1 to prevent the formation of BaC03 and BaS03. The SO, present' in the combustion gases would form a precipitat'e of BaS04. The solubility of BaSOl in the above solution was equivalent to 2 X lo-" gram of SO;. The BaC12 solution was analyzed for RaSO4 by measuring the turbidity with a spectrophotomcter. The per cent transmittance at' 520 n ~ p\vas measurcd and conipard to a blank (untreated solution) set a t 100% transmittance. Results in Table I indicate a combustion tcmpcrature of 825" C. is required for a quantitative Combustion to SO,. This is considcrably l o w r than the 1200" C.requircd for the same conversion using fused S,Oj ( 2 ) . The lower temperature is definitely an advantage and is attributed to differences in catalytic properties. Desiccants. T h e hydrogen in organic compounds undergoes oxidation to form water. This water must be removed to prevent its reaction with sulfur dioxide, which forms HLS03, a compound which will not pass through the chromatography column. Many niat,erials were tried as desiccants, b u t only calcium sulfate removed water without also rcmoving SOz. P,O6 was not tried. Anhydrous magnesium perchlorate produced explosions if t,he organic compound had not been correctly combusted. Thc most satisfactory mesh size n-as 50 to SO. T o check for the formation of H2S04 and H2S03,the tube was washed out after a combustion, and BaClz was added to the m-ashinga. N o precipitate formed. Ihen H20, was added to convert any S03-2 to and again no precipitate formed. Using R,,calculations, the amount of sulfatc required to produce a precipitatc 3hould have been around 10-9 gram. Even if an error of several hundred were prment, there would still be insufficient &SO4 and H2S03 to ruin tlie results. We feel that by having the drier next to the P t n-e avoided much of this. Rased upon the precision and accuracy of rcpetitive experinwnts, it is fclt that if any H$O, or H2S03lvere being formed and m-ere missed, then it must he doing so reproducibly, a situation which would not hinder tlie procedure. Trapping Sulfur Dioxide. T h e liquefication temperature of sulfur dioxide is -10" C. However, the flow rate through t h e trap and the surface area of the trap affect the rate of condensing t'hese vapors. It is necessary to have a trapping system t h a t quantitatively traps SO2 since a plug injection is required for chromatographic resolution. A reduction of the flow rate of oxygen through the combustion tube and cold trap resulted in incomplete combustion. The flow rate of oxygen was stabilized between r l
Table II.
Evaluation of Method
Sample Keight, Compound Phenyl sulfoxide Phenyl sulfone
Thianthrene Figure 2. column
Chromatogram using a dinonylphthalate
10 to 12 nil. per minute. Under these conditions, only liquid nitrogen quantitatively retained the SO2 in one trap. Laboratories t h a t do not have liquid nitrogen available may use tm-o traps and a slush bath. RECOMMENDED PROCEDURE
Procedure for Combustion of Sample. A combustion tube is cleaned and packed with 10% platinum asbestos (Fisher Scientific Co.) and platinum stars as shown in Figure 1. Eight centimeters of asbestos are packed in the tube, and each platinum asbestos plug is 2 em. thick. After placing t h e combustion tube in t h e Sargent microfurnace, the inlet is attached to the oxygen supply. -4 Pregl absorption tube, previously filled with 4 to 5 cm. of anhydrous calcium sulfate (the unused space is filled with glass wool), is attached to the exit end of the combustion tube b y rubber tubing covering a glass to glass joint. The absorption tube is joined to the trap b y pushing the drawn out end of the tube through the one-holed silicone rubber stopper attached to the trap as shown in Figure 1. The bypass of the trap is opened. The open end of the combustion tube is sealed with a cork, and oxygen is allowed to flow through the system at the rate of 10 to 12 ml. per minute for 30 minutes. During this time the long burner is hi~atrdto 860" C. and the mortar to about 180' C. to prevent condensation in the exit end of the tube. The trap is immersed in a Dewar flask containing liquid nitrogen, and the trap is opened to the system. A vacuum system is attached to the exit of the trap and the pressure is regulated by adjusting the screw clamp on the trap until oxygen will flow through the trap without condensing. The stopcocks are set to deadhead the system; the cork is removed from the end of the combustion tube. This allows a positive pressure in the tube during sample introduction. -4 3- to 10-mg. sample, previously weighed in a platinum boat to the nearest 0.001 mg., is introduced into the combustion tube and positioned 1 to 2 inches from the long burner. After replacing the cork in the end of the tube, the stopcocks are set to allow
the gases to pass through the trap. The short burner is heated to 850' C. and allowed to traverse toward the sample a t a slow speed. When the combustion is completed, the small burner is allowed to traverse the tube a second time to ensure a complete oxidation. To speed up the combustion process, the sample can be initially vaporized with a microburner. The small burner of the apparatus is used to sweep the system of any remaining sample. This requires only one sweep of the small burner. After the sample is combusted, the system is flushed with oxygen for 3 minutes. The trap is closed by adjusting the stopcocks, and it is then removed from the system. Analysis of Combustion Gases. A 20-foot column of 30% dinonylphthala t e which has been previously installed and conditioned is heated t o 90 to 96' C. T h e detector block is heated to the same temperature. iifter removing t h e cold t r a p from t h e D e n a r flask, it is connected to t h e gas chromatograph b y pushing t h e gas tubing through t h e silicone rubber seals. The bypass is opened and helium is passed through the instrument a t a rate of 45ml. per minute. The pressure of the gas will vary with the individual column. The potential of the detector block is adjusted, and a 1-mv. recorder is turned on. While the gas trap is allowed to warm to room temperature, about 4 to 6 minutes, the flow of helium is purging any foreign gases which may have been present in the inlet and outlet of the trap. K h e n the trap reaches room temperature as evidenced b y touching i t or the absence of any condensed material inside it, the stopcocks are opened. The stopcock furthest downstream is opened first to allow the release of pressure in the trap into the column. The other stopcock is then opened to flush the entire sample into the column. A second sample combustion can be started as soon as the first trap is removed from the combustion train. DISCUSSION
A series of different compounds was analyzed according to the above procedure. Table I1 shows the results of these determinations, and Figure 2 shows a typical chromatogram. Com-
hlg.
Mg. s d f u r Theory Found
3.767 5.668
0.597 0.898
0.616 0.930
11.746 2.503 2.916 4.627 10.231 6.240 3.111 4.042
1.723 0.367 0.428 0.679 1.501 1.848 0.921 0.677
1.644 0.386 0.423 0.652 1.432 1.877
Sulfuric acid 4,4,4-Trifluoro-1-( 2thieny1)-1,35.077 0.731 butadiene 2,2 Thio bisPchloro5.719 0.640 phenol 4.496 0.504 n-Buty1 sulfone 5.939 1.068 Mercaptoacetamide 8.042 1.223 carbamate Thiocarbamilide 5.575 0.855 3,3-Dibenzyl thiotane 2.500 0.315 Thiourea (found to be impure) 4.441 1.867 5.069 2.131 Quinine sulfate S o SO,peak
0.948
0.664
0.731 0.634
0.501
1.039 1.220 0.887 0.320 1.812 2.060
pounds containing F, C1, K j and 0, in addition to the C and 11, were successfully analyzed. A factor was obtained from the analysis of the phenyl sulfone samples by dividing the actual amount of sulfur in the .ample by the area in square inches under the SO,peak of the chromatogram. The wtxight of sulfur in each determination n-ar calculated as follon-s : Square inches under the peak X 0.604 mg. S per sq. in. The results gave an average deviation of 0.377@. There was a linear relationship between the area under the SO2 peak and the weight of S in the sample. Higher resistance thermistors should increase the sensitivity greatly. At the present time. the limit of detection is about 0.05 mg. Khile the ASTM Lamp method (1) and the Kickbold method (19) can possibly detect smaller amounts, this method is capable of being developed into a method whereby several elements can be determined simultaneously. Such cases as C and S and C. H, and S, and mixtures of halogens are currently being investigated. ACKNOWLEDGMENT
Financial support from the Kansas State University Bureau of General Research is gratefully acknowledged. VOL. 34, NO. 3, MARCH 1962
321
LITERATURE CITED
( 1 ) -4m. Soc. Testing Materials, D-1266,
Committee D-2 on Petroleum Products and Lubricants, Vol. 1, Am. SOC.Testing Materials, Philadelphia Pa., 1900. (2) Ibid., D-1552. (3) Duswalt, A. D., Brandt, W.W., ASAL. CHEW 32, 272 (1960). (4) Hoagland, C. L., J . Biol. Chem. 136, 543 (1940). (5) Huffman, E. W.D., IND.ENG.CHEN, ANAL.ED.12, 53 (1940). (6) Maresh, Charles, American Cyanamid
Co., private communication, March 20, 1961. (7) Schoniger, IT., “Facts and Methods for Scientific Research,” Vol. 1, No. 2, F and M Scientific Co., New Castle, Del., 1960. (8) Scott, R. L., Smith, D. E., Puckett, J. E., Heinrich, B. J., Technical Session on Analytical Research, 25th MidYear Meeting of the American Petroleum Institute, Division of Refining, Detroit, May 9, 1960. (9) Scott, W. W.,“Standard Methods of Analysis,” 5th ed., p. 904-25, Vol. I, Van Nostrand, New York, 1939.
(10) Steyermark, A, “Quantitative Organic Microanalysis,” 1st ed., p. 156, Blakiston, New York, 1900. (11) Sundberg, 0. E., Maresh, Charles, ANAL.CHEM. 32, 274 (1960). (12) Wickbold, O., Angew. Chem. 69, 530 (1900). RECEIVED for review September 7, 1961. Accepted December 14, 1961. Division of Analytical Chemistry, 140th Meeting, ACS, Chicago, Ill., September 1961. Abstracted from a thesis by Donald R. Beuerman submitted in partial fulfillment for the degree of Master of Science at Kansas Sate Univerisity.
Gas Chroma tog ra phic Determina tio n of C&, Produc ts from the Gamma Irradiation of Liquid Cyclopentane ARTHUR R. LEPLEY’
George Herbert Jones laboratories, University of Chicago, Chicago 37, 111.
b Fourteen CZ to Clo products have been identified gas chromatographically from the gamma radiolysis of liquid cyclopentane. Direct analysis of an entire irradiation sample of less than 100 mg. allowed both a qualitative and a quantitative determination of these products over a wide range of total gamma dosage. Use of weighed encapsulated samples and internal standards allowed a high precision of all trace products observed in the presence of up to 10,000 times their weight of cyclopentane.
G
CHROJIdTOGRAPHIC product analyses have been widely used in the study of radiation effects on organic materials (3, 7). Only since the advent of gas chromatography (2) has detailed evaluation of radiation processes become practicable. Despite this dependency, descriptions of this application of the technique are meager, which might be attributed to the routine nature of radiation product analyses. This work describes a modification of both radiation and analysis technique which simplifies procedures and allows precise determinations of radiation products. The direct analyses of irradiated samples were made using internal standards. The comparability and interpretation of results from micro and macro irradiations are discussed elsewhere (8). AS
APPARATUS
A modified version of the instrument described b y Dimbat, Portor, and Stross ( 4 ) was used. The temperature range, 0’ to 200’ C. was obtained b y placing a refrigeration radiator in the forced 322
ANALYTICAL CHEMISTRY
air circulation oven. The refrigerant was stored in the compressor ballast tank when working above 50’ C. A thermal conductivity cell, Gow Mac 9258 Pretzel, was used with a 2.5-mv. Weston recorder. REAGENTS
Cyclopentane. Phillip’s pure grade cyclopentane was purified b y gas chromatography on a tritolyl phosphate column. Reference Compounds. All b u t one of t h e required reference compounds were known. T h e following were obtained from Phillip’s Petroleum Co. as pure grade: ethylene, propylene, n-butane, isobutylene, isopentane, n-pentane, 1-pentene, 2pentene (cis and trans), 2,2-dimethylbutane, 2,3-dimethylbutaneJ methylcyclopentane, cyclohexane, n-heptane, and methylcyclohexane. I n addition, use was made of a Phillip’s gas mixture, KO. 40, as a source of ethane, propane, isobutane, 1-butane, and 2-butene (cis and trans). Methyl iodide, ethyl iodide, and mesitylene were obtained from Eastman Kodak. Cyclopentene was prepared b y dehydration of cyclopentanol over 85% phosphoric acid; b.p. 43.8’ C., n2g 1.4203. lJ5-Hexadiene was prepared from allyl bromide and magnesium; b.p. 59.6’ C., na2 1.4068. Allylcyclopentane was synthesized from cyclopentyl magnesium bromide and allyl bromide, following an existing procedure ( 1 ) ; b.p. 123.5-5.5’ C., n’d 1.4390. Vinylcyclopentane (9) ITas obtained on dehydration of P-cyclopentylethanol with 85% phosphoric acid; b.p. 98.5100’ C., n’g 1.4356. Dicyclopentyl, from the reaction of cyclopentyl bromide and sodium (11), had a b.p. of 190’ C., n2z 1.4645. Ethylcyclopentane was obtained by hydrogenation of vinylcyclopentane, in propionic acid
solution, over platinum oxide; b.p. 100-5’ C., na2 1.4185. Similarly, n-propylcyclopentane was made by hydrogenation of allylcyclopentane in ethanol solution; b.p. 130-1’ C., nabs1.4258. n-Pentylcyclopentane was obtained in a fraction, b.p. 17&80’ C., containing 10% n-decane, 50% npentylcyclopentane, and 40% dicyclopentyl, b y gas chromatographic analysis, t h a t resulted from the reaction of a n equimolar mixture of n-pentyl iodide and cyclopentyl bromide with sodium in di-n-butyl ether. Cyclopropylcyclopentane was prepared from the ditosylate of the known 2-cyclopentylpropane-1,3-diol (IO) by treatment with a mixture of zinc, sodium iodide, and sodium carbonate in boiling acetamide following the general method of Hugh and McBee as reported by Whitmore and coworkers ( I S ) . The procedure and characterization of the compound have been described elsewhere (@, COLUMNS
Preparation. All liquid phases were absorbed on 30- t o 60-mesh JohnsXanville Czz firebrick. T h e 20-foot 28% dimethylsulfolane (DMS) column contained 79 grams of packing. The TTP column held 63 grams of 28% o-tritolyl phosphate in 15 feet D C 550 silicone oil (20 grams of 25y0 liquid phase) was packed in a 6-foot column. Operation. T h e DRIS column was operated between -4’ and 0’ C. at a flow rate of 40 ml. per minute of H e for t h e identification of C1 through Cd products. Low flow rates of 25 and 20 ml. per minute of H e were emPresent address, Department of Chemistry, State University of New York, Long Island Center, Oyster Bay, N. Y.
