Allen, L. E., J . Agr. Food Chem. 6 , 778 (1958). (3) Blackburn, S., Lowther, A. G., Biochem. J . 48, 126 (1951). (4) Boyne, A, W., Carpenter, K. J., Woodham A. A., J . Sci. Food Agr. 12 832 (ld61). (5) bar enter, K. J., Biochem. J . 77, 604 (1960p. ( 6 ) Carpenter, K. J., Proc. Nufr. SOC. Engl. Scot. 17,91 (1958).
( 7 ) Carpenter, K. J., Ellinger, G. &I., Poultry Sci. 34, 1451 (1955). (8) Carpenter, IC. J., Ellin er, G. M., Munro, M. I., Rolfe, E. J., brit. J . Nutr. 11 162 (1957). ( 9 ) barter, F. L., Cirino, V. O., Allen, L. E., J . Am. Oil Chemisfs' SOC.38. 148
(mi).
(10) Conkerton, E. J., Frampton, V. L., Arch. Biochem. Biophys. 81, 130 (1959).
(11) Dustin, J. P., Czajkonska,
C., Moore, S., Bigwood, E. J., Anal. Chim. Acta 9, 256 (1953). (12) Frampton, V. L., U. S. Dept. of Agriculture, New Orleans, La., unDublished data. 1963. ( I $ ) Handwerck,' V., Bujard, E., Mauron, J., Biochem. J. 76, 54P (1960). (14) King, W. H., Kuck, J. C., Frampton, V. L., J . Am. Oil Chemists' SOC.38, 19
(1961). (15) Lea, C. H., Hannan, R. S., Biochim. Biophys. Acta 4, 518 (1950). (16) hlann, G. E., Carter, F. L., Frampton, V. L., Watts, A. B., Johnson, C., J . Am. Oil Chemists' SOC.39, 86 (1962). (17) hlartinez, W.H., Frampton, V. L., J . Agr. Food Chem. 6,312 (1958). (18) Martinez, W. H., Frampton, V. L., Cabell, C. A., Ibid., 9, 64 (1961). (19) Moore, S., Spackman, D. H., Stein,
W.H., ANAL.CIIEM.30, 1185 ( 1 9 5 8 ) ~ ~ (20) Schober, R., Prinz, I., Milchwisse schuft 11 , 466 (1956). (21) Seki, T., J . Biochem. Tokyo 47, 253 (1960). (22) Spackman, D. H., Stein, TT'. H., Moore, S., AKAL.CHEW30, 1190 (1958). RECEIVEDfor review October 29, 1962. Accepted August 5, 1963, Division of Analytical Chemistry, 142nd Meeting, ACS, Atlantic City, N. J., September 1962. S. Raghavendar Rao was granted a research associateship by the United Nations Children's Fund to participate in this research. The use of a company name and/or product by the U. S. Department of Agriculture does not imply approval or recommendation of the product to the exclusion of others which may also be available.
Determination of Hydrocarbons in Crude Cap itIa ry -Column Gas Chrorna tog ra phy
Oil by
RONALD 1. MARTIN and JOHN C. WINTERS Research and Development Deparfment, American Oil Co., Whiting, Ind.
b A capillary-column method has been developed for determining saturates through C7 and alkylbenzenes through Clo in crude oils. The hydrocarbons to be determined are separated from the crude with a packed prefractionator column, collected in a liquid-nitrogen trap, and then released into either of two capillary columns through a stream splitter. Components through C7 are well resolved in 4 hours on a 500-foot capillary column coated with 1 -octodecene. Alkylbenzenes through Clo are resolved on an 8OO-foot column coated with polyethylene glycol. Uncertainties in the results generally are less than 6% relative.
D
of composition is needed to characterize crude oils fully and t o provide insight into the formation of petroleum. Conventionally, individual components are determined by analyzing narrow-boiling distillation fractions with a variety of techniques (1-8, 6, 8, 14-16, 18, 20). dlthough results are usually satisfactory, these analyses are prohibitively lengthy and have been made on only a few crudes. Thus, generalizations on crudeoil composition had to be based on limited data. Packed-column gas chromatography has recently been used for determining individual components in crude oil (7,9,IP, 17,19). This approach, which has many advantages over distillation, has given analyses as far as CT (9), but resolution is less than ideal even with runs on three different columns. A new method was desired that would ETAILED KNOWLEDGE
1930
ANALYTICAL CHEMISTRY
provide a n improved resolution of components through C7 and would be faster. There also was a need to extend the analyses to alkylbenzenes through CIo, because these components have been determined in only two crudes-those both by distillation (14, 28). Capillary columns, which have excellent resolving powers (4, 6),were investigated. This led to the development of a new method for determining saturates through C, and alkylbenzenes through Clo. The method is accurate, can detect trace components, and does not need a prior distillation. The relative speed of the new method has allowed many crude oils to be analyzed. Analyses with this method of 24 crude oils (IO,11) have led to new generalizations on composition, and have provided a basis for speculation on petroleum origin. EXPERIMENTAL
The apparatus is diagrammed in Figure 1. Hydrocarbons of a selected boiling range are separated from the crude oil by the prefractionator column and are collected in the liquid-nitrogen trap. The prefractionator, a short packed gas chromatographic column, separates approsimately by boiling point. After the desired boiling-range fraction has been trapped, the prefractionator is bypassed by changing the position of the 4-way valves. The trap is then warmed and the hydrocarbons are carried into the capillary rolumn through the stream splitter. The individual components are detected by hydrogen-flame ionization as they emerge from the capillary column. Volatile compounds remaining on the
orefractionator are removed bv backflushing. For hydrocarbons through C7, a caDillarv column coated with 1-octad&ene " is used. For alkylbenzenes through Clo, one coated with polyethylene glycol is used. Hydrocarbons through C7. Numerous liquid phases were tested for separation of hydrocarbons through C7. As shown in Figure 2 for a typical crude oil, excellent separations were obtained with a 500-foot by 0.010-inch stainless-steel capillary coated with 1-octadecene. Abbreviations on the chromatogram are identified in Table I. Except for cycloheptane, which has been reported as a trace component in only one crude (id), all hydrocarbons through C, and the 10 lowest-boiling Cs's are well resolved. Methane and ethane, however, are not determined because of nonquantitative collection in the liquid-nitrogen trap. The column was operated a t 30" C. with a helium exit flow of 0.85 cc. per minute at a gauge pressure of 35 p s i . Just as on silicone-coated capillary columns ( I S ) , elution positions of some hydrocarbons change with temperature on the octadecene column. A temperature of 30' C. gives optimum resolution. An increase or decrease of only 3' C. causes a t least one pair of compounds to elute together. With a n increase in temperature, cycloparaffins and aromatics are retained longer relative to paraffins. Alkylbenzenes through C,O. Dehermination of alkvlbenzenes through Clo is complicated b y interfering sat& rates that accompany the alkylbenzenes from the prefractionator column. These saturates would hopelessly cover the alkylbenzenes if a column separating in boiling-point order were used. However, this interference is minimized b y
using a polar liquid phase t h a t selectively retains alkylbenzenes past saturates of similar boiling points. Good separations w r e obtained with a n 800-foot by O.Cl0-inch column coated with polyethylene glycol (Union Carbide Carbowax 400). This column has high separating power for individual alkylbenzenes and also is selective in retaining the alkylber zenes past saturates. Separation of alkylbenzenes through CIo is shonn in Figure 3 for a typical crude; saturrttes are not included, nor is lJ2,3,4-tetramethylbensene, the highest-bo ling Clot which elutes 70 minutes p u t lJ2,3,5-tetramethylbenzene. Abbreviations on the chromatogram are identified in Table 11. The column \+a
