rough surfaces of opaque materials. The emission method could certainly be directly applied to various lubrication lxoblems with existing instrumentation a< it was possible to obtain evidence of interactions between oleic acid and a metal surface. an analytical method, the emission technique offers the advantages of simplicity of sample preparation and examination. Empirical methods could be developed for specialized applicationb for routine work, such as quality control of pigments or coatings. The
samples must be hot, so that heat-sensitive materials could not be reproducibly examined, at least at present. This particular failing can be turned to advantage, however, for studies of thermal degradation of opaque or not easily handled materials such as rubbers, leather, plastics, coatings, or various fabrics. The method has potential application for the study of boundary lubrication, solid lubricants, solid-state reactions, and gas-solid interactions a t the surfaces of wires, ribbons, metal single crystals, and catalysts.
LITERATURE CITED
(1) Eischens, R. P., Pliskin, W. A , , Advan. Catalysis 10, 51 (1958). RECEIVEDfor review July 13, 1964. Accepted September 9, 1964. Report of work done, in part, under contract with the U. S. Department of Agriculture and authorized by the Research and Marketing Act. The contract was supervised by the Northern Utilization Research and Development Division of the Agricultural Research Service. Support from the Petroleum Research Fund of the American Chemical Society by Grant S o . PRF1247-A3 is acknowledged, as is National Science Foundation Instrument Grant No. GP1434.
Analysis of a TrinucIear Aromatic Petroleum Fraction by High Resolution Mass Spectrometry H. E. LUMPKIN Research and Development, Humble Oil and Refining Co., Baytown, Texas
,This paper describes the first use of high resolution mass spectrometry combined with the low ionizing voltage technique for the analysis of a complex mixture. Identifications are achieved by precise mass measurement of the molecular ion, assumption of a reasonable structure, then measurement of fragment ions to prove or disprove the assumed structure. The analysis of a trinuclear aromatic fraction from the 347-60" C. boiling range of a high sulfur and nitrogen crude is used as an example of these methods. In addition to six condensed aromatic hydrocarbon types, five sulfur, two oxygenated, and one nitrogen compound type were found. A quantitative analysis for each of these types based on low voltage sensitivities is given; however, accuracy is limited to some extent by the availability of pure compounds. HE M A J O R use of high resolution mass spectrometry has been the identification and structural determination of pure compounds, or of the major component of a simple misture. Beynon has pioneered this field and his book (1j is re,:lete with esamples of the use of this methcd. High resolution mass spectrometry and organic chemistry are happily joined in the excellent work of Biemann and his associares (2-4, 8), particularly in the structural elucidation of many complex Compounds encountered in natural products. The low ionizing voltage method introduced by Field and Hastings (6) has continued to be developed in this
laboratory (9, 10) as well as in others (5) and is now in widespread use as an analytical technique. One of the major disadvantages of the technique when applied to complex petroleum mixtures is the ability to distinguish only seven classes of compounds. For example, alkyldibenzothiophenes cannot be distinguished from alkylnaphthalenes as both form molecular ions in the C,,H2,-iz mass series. When high resolving power is available, however, this disadvantage no longer esists and the number of compound types which can be determined in admisture is limited only by the resolution and limits of detectability of the instrument. This paper describes the use of high resolution mass spectrometry with the
6 5 6 - 6 8 0 ' F. BOILING RANGE FRACTION
TRI NUCLEAR AROMATIC
Figure 1 . Separation aromatic fraction
of
trinuclear
low ionizing voltage technique for the analysis of a complex petroleum mixture. EXPERIMENTAL
A sample from the trinuclear aromatic portion of a coker gas oil was selected for this study. The sample had been suhjected to distillation, thermal diffusicn, and chromatographic separation (Figure 1) some years ago. Although it was not kept from contact with air during its soi)aration, the fractions were tightly sealed during the interim pericds. =\ double focusing in.trunient having an electrcstatic analyzer radius of 15 inches and a magnetic analyzer radius of 12 inches was used in this investigation. The instrument is calmble of a resolution of over 1 to 10,000 and uses the X e r (12) peak inatrhing system for mass measurement (manufactured by -1ssociated Elect r i d industries, Lt,d,, it is designated as lIS9). Recorded spectra of the sample were obtained a t four operating modes: low resolution high voltage (70-volt ionizing voltage): low resolution low voltage (about 8-volt' imizing yoltage), high resolution high voltagc, and high resolution low vc~ltage. Sc>lection of parent peaks for further inve was made from the lcw resolution low voltage run. Howevcr, mass measurements must be made at high resolution, and both high and low voltage spectra a t high resclution were used to locate and recognize the ma+ drsired and to select the 1)eaks anlong the multiplets which were the molecular ions to be measured. .I minimum amount of low voltage sensitivity data on available ]jure compounds were obtained. These data indicated that the relative sensitivities VOL. 36, NO. 13, DECEMBER 1964
2399
Table
1.
Mass series CJL-s - 10
- 12 - 14
- 16 - 16 - I8 - 20
of
Summary Analysis Petroleum Fraction
Compound types Indanothiophenes Indenothiophenes Indenes Dibenzothiophenes Saphthalenes Acenaphthenothiophenes Dibenzofurans Acenaph thenes Carbazoles Fluorenones Fluorenes Phenanthrenes Benzodithiophenes Cyclopentaphenanthrenes
a
On alkyl substitution, parent peaks of 224, 238, etc., would be formed, and p bond rupture would form an abundant mass 181. The absence of the mass 167 oxygen-containing inn is not readily explained, but it may be due simply to low abundance.
2 4 7 9 2 8
1 1 13 3 16 8 2 8 3 0 ~
100 0
Table 11.
Dibenzofuran CItHgO 1101. n't. 168
Wt. "/c 42 1 8 0 4 39 7 2 3 15
Mass Measurements in - 14, - 15 Series
1101. formula
hIeasd. m a w Calcd. mass C,,H,, 167 0866 f 6 167 0861 C;;H9b 181 0662 f 9 181 0653 181 0891 C13HIIN 181 0897 i 9 181 1021 f 9 181 1017 CI4H13 195 0271 f 6 195 0269 CI?H,S 195 0810 C14H110 195 0812 f 6 195 1048 Cl4HiaN 195 1065 f 8 195 1171 f 6 195 1174 CisHij 209 0425 C,,HaS 209 0421 i 6 209 0971 f 10 209 0966 C;;H,b 209 1330 CI6Hl7 209 1317 i 10 238 0816 ClsH14S 238 0816 i 8 Cl,HI,O 238 1356 i 10 238 1358 ClsH,, 238 1717 i 7 238 1721 Estimated experimental limits of mass measurement x 1 0 F from experimental mass ratios. 0
among various classes of compounds were quite similar to those observed previously (IO) on a 180' magnetic deflection instrument. From the sensitivity data and the high resolution low voltage scan, a quantitative analysis of the fraction was calculated by conipound type and by carbon number. A summary of this analysis is given in Table I.
Figure 2. m / e 195
and CnHSn--15 series are given in Table 11. These data indicate the precision of the measurements and will serve as a basis for identifications in these series, as discussed below. The C,,Hv,-14,-1s series was one of the most interesting series of peaks in the sample. The low voltage high resolution spectra showed trildets in the CnH2n-14series a t masses 224, 238, 252, 266, 280, and 294. Ma:: measurements at 238, 266, and 294 established that the same compound types, one containing sulfur, one an oxygen, and the third a hydrocarbon, extended throughout the molecular weight range of the sample. An investigation of the fragment peaks was then necessary to establish as much structure as possible, a t least to determine if the sulfur and oxygen were in side chains or in the nuclei. RIass measurements a t masses 209 and 195 still revealed sulfur and oxygen; however, a t mass 181 no sulfurcontaining ion in the series could be found. It was felt that the sulfur was in the nuclei and that a compound type of nuclear molecular weight of 196 or 210 was indicated. .Isthe C13HjSion a t mass 195 is likely due to the abundant dibenzothiolihene class, the following structure was assigned to the sulfur compound type in the C,H2,,_14series:
.\
n
DISCUSSION AND RESULTS
By far the most interesting as well as time-consuming parts of the investigation were the mass measurements, calculations, and interpretations leading to the identifications of the compound types. Many mass measurements were necessary. Occasionally the instrument was noisy or the resolution was insufficient in a series of measurements and the measurements had to be repeated. Often a compound type could not' be identified from its molecular formula alone and it was necessary to measure a qeries of fragment peaks. -\ll of the mass measurements made in this study will not he given here; however, some selected measureinents and assigned molecular formulas in the CnH?,,-11 2400
ANALYTICAL CHEMISTRY
High resolution spectra of
Acenaphthenothiophene CIIHloS 1101. Wt. 210 On alkyl substitution, parent peaks of 224, 238, etc., would result; the nucleusH would giT e mass 209. I t mass 181 the oxygen and hydrocarbon ions were still prerent, but a t mass 167 only the hydrocarbon ion, CISHI1,was found. The o ~ j g e ncoinpound type has been aqsigned as dibenzofuran. Benzofuran, an analogous 2-ring aromatic compound, was identified in a shale oil fraction by \.'an Meter
et a / . ( 1 1 )
The hydrocarbon is identified as the familiar acenapthene.
@I c
Acenaphthene ~ ~ nIoi. H wt. ~ 154 ~
h n abundant peak due to C13H11 would be expected from alkyl acenaphthenes. When the low voltage spectra were examined it was noted that parent peaks existed a t masses 181 and 195. No combination of C, H, 0.and S gices odd numbered compound molecular weights. whereas 1, 3, 5, etc., S atoms in combination with C, H, 0, and S alnays give odd molecular weights. Mass measurements revealed a nitrogen compound type a t masses 181 and 195. This leads to a proposed qtructure for the nitrogen compound type'
QqJQ k ClXHgK
Carbazole 3101. wt. 167
Mass measurements made a t mass 195 on the single peak still present a t 8.0 e.v. showed it to be Ci4H1J, corresponding to ethyl or dimethyl carbazole. Helm et al. ( 7 ) have shown that carbazoles are found in some crude sources. The power of the low voltage technique in combination with high resolution is indicated in Figure 2. At 8.0 e.v. only the molecular ion of the substituted carbazole appears a t m e 195. A s the electron energy is increased, fragment ions from the other compound types appear in order of increasing appearance potential. until a t the normal i o volts, four peaks due to sulfur-, oxygen-, and nitrogen-containing, and the hydrocarbon molecules are seen. LITERATURE CITED
(1) Beynon, J H , "11ass Ppectrometrj and Its Application t o Organic Chemistrq, Elsevier Publishing Co , Amsterdam, 1960, and references cited therein (2)_Biemann,K , d n n Rei Biochem 32, 1 x 1 (1963)
( 3 ) Biemann, K., Bommer, P., Burlingame, A. L., Mcl'lurray, W. J., Tetrahedron Letters 1963 (28), p. 1969. (4) Bommer, P., McMurray, W., Biemann, K., J . A m . Chem. SOC.8 6 ,
1439 (1964). (5) Crable, G. F., Kearns, G. L., Norris, M. S., ANAL. CHEM.32, 13 (1960). (6) Field, F. H., Hastings, S. H., Zbzd., 2 8 , 1248 (1956). (7) Helm, R. V., Latham, D. R., Ferrin,
(12) Pu'ier, A. 0 . ) "Nuclear Masses and
C. R., Ball, J. S., Ibid., 32, 1765 (1960). (8) Jongh, Don C. de, Biemann, K., J . A m . Chem. SOC.8 6 , 67 (1964). (9) Lumpkin, H. E., A~YAL.CHEM.30, 321 11968). (10) Lumpkin, H. E., Aczel, T., Ibid., 36, 181 (1964). (11) Meter, R. A. van, Bailey, C. R., Smith, J. R., Moore, R. T., Allbright, C. S., Jacobson, I. A., Jr., Hylton, V. M., Ball, J. S., Ibzd. 2 4 , 1758 (1952).
Their Determination," H. Hintenberger, ed., pp. 89-102, Pergamon Press, Xew York, 1959. RECEIVEDfor review August 3, 1964. Accepted September 28, 1964. 12th Annual Conference on LIass Spectrometry, ASTM Committee E-14, Montreal, Canada, June 1964.
Determination of Beta-Olefinic Methyl Groups in Esters of Fatty Acids by Nuclear Magnetic Resonance CURTIS A. GLASS and HERBERT J. DUTTON Northern Regional Research laboratory, ARS, USDA, Peoria, 111.
b An analytical method for determining 15,16-unsaturation in fatty acids by nuclear magnetic resonance spectrometry is described. Utilized in the determination are the low field member of the p-olefinic methyl proton triplet and the central peak of non/3-olefinic methyl proton triplet. The areas of these signals are deiermined by the instrumental integrator and b y paper tracings, and precision of the two methods is compared. Application to the kinetics of hydrogenation is presented.
3.0
2.0
4.0
5.0
,
7.0
6.0
,
8.0 '
I
9.0
,
'
10.0 7 1
Methyl Oleate
A
in flavor and odor stability of hydrogenated vegetable oils is t,he amount of 15,16unsaturation (p-olefinic) that remains after reduction (2). Det,ermining the amount of this structure is difficult. A4vailable oxidative cleavage methods ( I , 6) are not quantitative because the low-boiling propionic acid fragment is partially lost in solvent evaporation steps. The possibilit,y of using nudear magnetic resonance (XMR) to determine this structural arrangement was first considered by Storey ( 7 ) and by Johnson and Shoolery (4) u-ho noted that the resonance of the terminal methyl protone was shifted slightly downfield by a p-olefinic bond. The latter men concluded that a quant,itative measure of the amount of this grouping was not possible because of overlapping signals. In the present report, various procedures for exploiting this second-order shift, in resonance have been studied, a quantitatire procedure is described, and precision has been determined. N IMPORTANT FACTOR
EXPERIMENTAL
YMR spectra were measured with a I'arian -4-60 spectrometer. Samples were studied as 20% solutions of
r*.
Methyl Linolenate
i i
/I
I
I
L i 2.0
I
3.0
7
,
,
4.0
Figure 1.
J,
v : 5.0
,
,
6.0
!
,
1
7.0
I
8.0
9.0
10.0
r
NMR spectra of methyl esters of fatty acids
methyl esters in carbon tetrachloride with tetramethylsilane (TMS) and benzene present as internal references. The standard Varian 5-nim. 0.d. tubes and a room-temperature probe were employed throughout. Chemical shifts are given in parts per million a5 7 values (10.00 - p.p.ni. from TMS). The oleate, linoleate, and linolenate were obtained from the Hormel Foundation.
RESULTS AND DISCUSSION
Figure 1 presents the S M R spectra of methyl oleate and niethyl linolenate The sharl) signal at 2.65 7 is a second reference, benzene. The folloiving assignments for methyl oleate are as made previouily ( 3 ): the signal a1woximating a tripkt at 4.63 7 , Olefinic protons, a sharp signal at 6 . 3 i 7 , niethoxy VOL. 36, N O . 13, DECEMBER 1964
2401
