The number of theoretical plates in a column is related to Q by the following formula :
r
=
16Q2
This definition is, of course, as useful as that of the authors. However, in order to express this quantity as a simple product of relative separation and relative peak sharpness, it becomes necessary to define these latter quantities as
(9)
Resolution, R. A quantitative evaluation of the degree of resolution obtained between two chromatographic peaks, as influenced by both the chemical properties of the system and efficiency of t h e column, can now easily be calculated from measured values of relative peak separation and relative peak sharpness. R
&Si2
and
&=-
(10)
Figure 3 illustrates the appearance of chromatograms of different degrees of resolution. Because a chromatographic peak approaches in shape a Gaussian distribution, a complete physical separation of sample components can never be attained ( 3 ) . Even where the detector output appears to return to zero between adjacent peaks, the component producing each peak nonetheless contributes to some small extent to the area of the other. The degree to which this effect is evident is determined by the ratios of the concentrations of the two components in the sample. If, for esample, 0.01% of component 5 is present in the peak produced by component y, the error is negligible or not, depending upon whether 2 and y are present in equal or 1000 to 1 ratios. Thus, it is not possible to assign a value of R adequate t o ensure good resolution in all cases. The necessary value of R will depend upon sample component concentration ratios and the required dpgree of analytical accuracy. For
tl
w1 I
0
3
2
t2
4
Time
Figure 3.
+ + w2
Resolution
Hypotheticai chromatograms, arbitrary units R = QS
the ordinary case, where neither peak exceeds the deflection span of the recorder, a n R value of about 2.5 represents complete resolution within the precision of the usual recording instrument. A simple formula correcting for the effect of concentration ratio is under development and will be published in the future. Having recorded the values d S,,for various compounds on various column packings, one now can calculate their relative separations and the value of Q necessary to attain a required degree of resolution with any of the packings tested, by application of the relationships presented above.
These expressions, while usable, are unnecessarily cumbersome, because their added complexity contributes nothing to their value. The authors therefore prefer their simpler expression for resolution. LITERATURE CITED
(1) Ambrose, D., Keulemans, A. I. M.,
DEFINITION OF RESOLUTION
Purnell, J. H., AKAL.CHEM.30, 1582 (1958). ( 2 ) Consden, R., Gordon, A. H., Martin, A. J. P., Biochem. J . 38,224 (1944). (3) James, A. T., Martin, A. J. P., Ibid., 50, 679 (1952). (4) Keulemans, A. I. M., “Gas Chromatography,” Reinhold, New York, 1957. (5) Martin, A. J. P., Synge, R. L. M., Biochem. J . 35, 1358 (1941). (6) Phillips, C. S. G., Second Symposium on Gas Chromatography, Amsterdam, May 22, 1958. (7) Sullivan, L. J., Lotz, J. R., Rillingham, c. B., ANAL.CHEM. 28,495 (1956). (8) Wiebe, A. K., Delaware Section, .4CS, February 18, 1956.
Phillips (6) has proposed a definition of resolution
RECEIVED for review February 13, 1957. ilccepted April 16, 1958.
Identification of Low-Boiling Sulfur Compounds in Agha Jari Crude Oil by Gas-Liquid Chromatography H. J. COLEMAN, C. J. THOMPSON, C. C. WARD, and H. T. RALL Petroleum Experimenf Station, Bureau o f Mines, U. S. Department of the Interior, Bartlesville, Okla. Gas-liquid chromatography and supplemental mass spectrometry analyses were used to identify eleven sulfur compounds in Agha Jari, Iran, crude oil. This investigation produced new analytical data concerning the low-boiling sulfur compounds in Agha Jari crude oil, information which is of direct interest to the refiner. A comparison with similar data from other crude oils may shed some light on the origin of petroleum and of the sulfur compounds found in it.
1592
0
ANALYTICAL CHEMISTRY
E
publications ( 2 , 8,9) from this laboratory have reported the separation and identification of sulfur compounds in Wasson, Tes., and W l mington, Calif., crude oils using such techniques as isothermal distillation, adsorption, fractionation, and infrared and mass spectrometry. Although these procedures are reliable, many of the steps are time-consuming, and relatirely large quantities of crude oil must be processed to produce enough final sulfur compound concentrate for fractionation ARLIER
and subsequent identification of the components by mass or infrared spectrometry. The use of gas-liquid chromatography now makes it possible to circumvent some of the more objectionable steps in the separation and identification procedures employed previously. Literature references concerning the application of gas-liquid chromatography to mixtures of sulfur compounds are limited. Sunner, Karrman, and Sunden ( 7 ) report the quantitative separation of a number of aliphatic
....................................................................
A G H A JARI CRUDE O I L
I I i
n
63.85 Kg.
AGHA JAR1 S U L F U R CONCENTRATE
l r o t h r n a l Dirthiation (Atmrxphnic Press.)
(0.211%)
--1
AROMATiC SULRIR CONCENTRATE
--
II
ALCOHOL FFACTIONS
II
HYDROCARBON DISCARD
I
n
J
,
,
BO
1 I
BOILING RANGE-338'i0O.C WT PERCENT SULFUR-255%
,
,
70
, 60
,
,
1
,
5r
,
,
,
,
,
,
2C
30
40
,
,
10
..................................................................... A G H A JARI S U L F U R C O N C E N T R A T E
' 7 '
PLUS ADDED COMPOUNDS
Sulfur E x t r a t l w
Alumina Pwsolatim 3 - 2-Butaneth8ol 4 . 3-Me-Z-thiobutone
80
3 0 do
70
....................................................................
FINAL CONCENTRATE
A G H A JAR1 S U L F U R C O N C E N T R A T E PLUS ADDED COMPOUNDS
Figure 1. crude oil
Summary of processing of Agha Jari, Iran,
I
N ~ t eenh~ncemlnt ~t v i m b e r e d peoks
- I-Propmethi01
2 - 2-Th~obutone 4 - 3-Thtopentane
thiols; Ryce and Bryce (6) have investigated the separation of a synthetic blend of volatile organic sulfur conipounds; Desty and Khyman ( 4 ) and later Desty and Harbourn (3) included several classes of sulfur compounds in their evaluation of column packings. A recent paper by Thompson, Coleman, K a r d , and Rall (IO) describes the identification of 3-methylthiophene in Wilmington, Calif., crude oil by this technique. Since the present paper was written, Amberg ( I ) has reported the relative retention times of eight thiols, five sulfides, and 11 thiophenes. The present paper reports the identification of 11 sulfur compounds by applying gas-liquid chromatography to a sulfur compound concentrate from Agha Jari, Iran, crude oil. The identifications n-ere confirmed by trapping the material producing the chromatographic peaks and analyzing the trapped niaterials by mass spectrometry. These identifications were accomplished accurately and 11-ith less expense of time and effort than in previous studies. Sample requirements 1% ere less than those necessary to produce equal resolution by other known techniques. APPARATUS
The gas-liquid chromatography column was a copper tube, inch in diameter and 6 feet long, which was filled with 40- to 50-mesh, acid-washed
T I M E , MINUTES
Figure 2. Gas-liquid chromatographic Jari 38" to 100" C. sulfur concentrate
firebrick impregnated with 17y0 by n-eight of Dow Corning 550 silicone oil. The operating temperature of the column m s 38" C., and the helium carrier gas flow rate was 100 ml. per minute. The detecting system consisted of a thermistor-type cell in a conventional bridge circuit. This cell has a sensitivity of about 1500 ml. X mv. per mg. of n-butane, using the Shell (6) system of designation. EXPERIMENTAL
The aromatic sulfur compound concentrate, from which the indiridual compounds were separated and identified, was prepared as shown in Figure 1. The conditions were such that the compounds found are thought to have been present in the crude oil and not produced in any processing steps. At no time tvas the crude oil or any of its fractions subjected to a temperature higher than 100" C. A 0.02-ml. sample of the aromatic
analysis of Agha
sulfur concentrate (shonn in the final block of Figure l ) , representing 0.014% of the original crude oil, was examined by the gas-liquid chromatographic technique, and the chromatogram shonm in Figure 2 (top) was obtained. The emergence times of the sulfur conipounds in the boiling range of 38" to 100" C. had been determined previously, and, rvith this information, a tentative identification could be assigned to most of the peaks in this chromatogram. The addition of small amounts of pure sulfur compounds to the sample cnhanced the proper peaks and produced no extraneous peaks (Figure 2. center and bottom), thus corroborating their presence in the concentrate. Final proof of compound identity was obtained by trapping, in liquid air-cooled traps, the compounds emerging from the column during formation of a peak and analyzing the trap contents by mass spectrometry. Eight compounds VOL. 30, NO. 10, OCTOBER 1958
1593
Table I. Sulfur Compounds Identified in Agha Jari, Iran, Crude Oil
Compound 2-Propanethiol 2-Methyl-2-propanethiol 2-Thiabutane 3-Methyl-2-thiabutane 2-Butanethiol 3-T hiapentane 2-T hiapentane 2-Methyl-3-thiapentane
Boiling Pooint, C. 52.56 64 22 66.65 84.8 85.0 92.10 95.6 107.38
Tentatively Identified I -Propanethi01 67.8 2-Methyl-1-propanethiol 88.5 2,2-Dimethyl-l-propanethiol 103.7
(Table I) were thus definitely identified. The presence of three compounds identified by emergence time and peak enhancement could not be conclusively confirmed by mass spectrometry of trapped fractions because of insufficient sample. The identification of these compounds must remain tentatire until confirmatory proof of their presence is secured by independent means. Three other compounds, l-butanethiol (98.4’ C.), 2-methyl-2-butanethiol (99.2’ and 3,3-dimethyl-2-thiabutane (99.0” C.),were sought but not found. The emergence time of each
e.),
of these three compounds coincides with a major component in the concentrate, and trace amounts mould be most difficult to separate and identify by gasliquid Chromatography. These compounds have been identified (9) in small or trace amounts in Wasson, Tex., crude oil and are believed to be present only in trace amounts, if a t all, in Agha Jari crude oil. CONCLUSIONS
The following eight sulfur compounds were positively identified in Agha Jari crude oil by means of gasliquid chromatography and supplemental mass-spectrometry analysis: 2propanethiol, 2-rnethyl-2-propanethiolJ 2-thiabutane, 2-butanethiol, 3-methyl2-thiabutaneJ 3-thiapentaneJ 2-thiapentane, and 2-methyl-3-thiapentane. I n addition, 1-propanethiol, 2-methyl-lpropanethiol, and 2,2-dimethyl-l-propanethiol were tentatively identified in the same crude oil. ACKNOWLEDGMENTS
The authors wish to acknovledge the aid of N. G. Foster and Pearl Tribble in supplying the mass spectral analyses of pertinent fractions used in this investigation.
LITERATURE CITED
(1) Amberg, C. H., Can. J . Chem. 36,
590-2 (1958). (2) Coleman, H. J.. Adams, K. G., Eccleston, B. H., Hopkins, R. L., Mikkelsen, Louis, Rall, H. T., Richardson, Dorothy, Thompson, C. J., Smith, H. M., ASAL.CHEX 2 8 , 1380-4 (1956). (3) Desty, D. H., Harbourn, C. L. 8., Division of Analvtical and Petroleum Chemistry, Sympbsium on .Advances in Gas Chromatography, 132nd Meeting, ACS, Xew York, K. Y., September 1957. 14) Destv, D. H.. Khvman, B. H. F.. ASAL. HEM. 29’. 320-9 (1957). (5) Dimbat, hl., Porter,‘ P. E., Stross, F. H., Zbid., 28, 290-7 (1956). (6) Ryce, S. A., Bryce, W. A,, Ibid., 29, 925-8 (1957). ( 7 ) Sunner, S., Karrman, K. J., Sunden, V., Mzkrochim. Acta 1956, 114P51. (8) Thompson, C. J., Coleman, H. J., Llikkelsen, Louis, Yee, Don, Ward, C. C., Rall, H. T., ANAL. CHEY. 28, 1384-7 (1956). (9) Thompson, C. J., Coleman, H. J., Rall, H. T., Smith, H. M., Ibid., 27, 175-85 (1955). (10) Thompson, C. J., Coleman, H. J., Ward, C. C., Rall, H. T. Southwest Regional Meeting, ACS, Tulsa, Okla., December 1957. RECEIVEDfor review January 11, 1958. Accepted May 23, 1958. Division of Petroleum Chemistry, 133rd Meeting, ACS, San Francisco, Calif., April 1958. Investigation performed as part of American Petroleum Institute Research Project 48.4 on “Production, Isolation, and Purification of Sulfur Compounds and Measurement of Their Properties,” which the Bureau of Mines conducts a t Bartlesville, Okla., and Laramie, Kyo.
Near-Infrared Analysis of Mixtures of Primary and Secondary Aromatic Amines KERMIT WHETSEL, WILLIAM E. ROBERSON, and M A X W. KRELL Tennessee Eastman Co.,Division o f Easfman Kodak
b The analysis of mixtures of primary
.
and secondary aromatic amines by near-infrared spectroscopy was investigated. By utilizing the N-H overtone and combination bands near 1.49 and 1.97 microns, respectively, mixtures of aniline and N-ethylaniline containing up to 99% of either constituent can be analyzed with standard A deviations no greater than & 1%. modification of the method permits the determination of aniline with a standover the 0 ard deviation of &O.l% to 10% concentration range. Aliphatic amines and tertiary aromatic amines do not interfere. Similar methods can be used to analyze a variety of other mixtures of primary and secondary aromatic amines.
D
past few years nearinfrared spectroscopy has been recognized as another valuable techCRING THE
1594
ANALYTICAL CHEMISTRY
Co.,Kingsport,
Tenn.
nique for the analysis of organic compounds. Methods which utilize the first overtone 0-H and K-H stretching bands near 1.4 and 1.5 microns, respectively, have been reported for the determination of water in hydrazines (S) and in nitric acid (9),the analysis of mixtures of A‘-alkyl and A‘-alkyl-K-hydroxyalkyl aromatic amines ( 7 ) ,and the determination of unacetylated hydroxyl groups in cellulose acetate ( 6 ) . Goddu has discussed the advantages of studying the fundamental 0-H stretching bands near 2.8 microns Ivith high-resolution quartz optics and lead sulfide detectors (9). He has also described the determination of terminal and cis unsaturation using overtone and combination bands near 1.6 and 2.2 microns ( I ) . The possible application of near-infrared data to the problems encountered in lipide chemistry has been discussed by Holman and Edmondson (4).
Primary aromatic amines are characterized by two intense absorption bands near 1975 and 1500 mp, Kaye (5) has assigned the band at 1975 mp to a combination of N-H stretching and bending modes and the one a t 1500 mp to the first overtone of the N-H stretching vibration. Secondary aromatic amines exhibit the first overtone band near 1500 mp but not the combination band. The present investigation vias concerned with the application of these absorption differences to the quantitative analysis of mixtures of primary and secondary aromatic amines. APPARATUS AND MATERIALS
A Cary Model 14MS spectrophotometer equipped with a log absorbance slide-Tvire was used. (A per cent transmittance or a n absorbance slide-wire could have been used equally well except for the difSpectrophotometer.
