High Resolution Mass Spectrometry Interpretation of Spectra of Petroleum Fractions E. G. CARLSON, G. T. PAULISSEN,
R. H.
Housfon Research laboratory, Shell Oil ,A coinicident-field mass spectrometer, which has a resolving power approaching one order of magnitude higher than that of the conventional analytical instrument, has been adapted for operation with highboiling petroleum fractions. It is possible to obtain resolution of ions having the same nominal mass, but arising from different combinations of elements in the molecules which constitute petroleum. New techniques for the interpretation of spectra have been developed in conjunction with the highresolution instrument. By means of these techniques evidence has been found for the presence in petroleum fractions of several molecular types for which there has been only indirect evidence or which have not previously been reported.
Ass SPECTROhIETRY has gained wide acceptance in the petroleum industry for the analysis of hydrocarbon mistures boiling in the distillate range. Commercial mass spectrometers for use in this area have been of the single-focusing type with limited resolution. This limitation restricts their usefulness to materials lighter than petroleum residues-Le., to distillate fractions which have a minimum amount of overlapping types (CnHln+rdiffering in z-number by 14 units). The extremely useful information obtained niakes it highly desirable to extend the use of this technique to the study of residue fractions and of distillates containing overlapping types. The objections stemming from resolving power can be largely overcome with a double-focusing mass spectrometer. Several instruments of this type which are suited to the analysis of organic materials have been described (6, 9). The present work has been concerned with a double-focusing coincident-field mass spectrometer which was adapted for operation with highboiling petroleum fractions.
HUNT, and M. J. O’NEAL, Jr. Co., Houston I , Tex.
Two general features of the basic instrument combine to limit its useful mass range. I n the first place mass dispersion occurs between the plates of the electrostatic analyzer as they lie within the magnetic sector. Thus, part of the ion beam always impinges on the plates. Secondly, a coincident-field instrument of this type requires less accelerating voltage for a given m/e (mass-to-charge ratio) than an equivalent tandem unit. This latter point may be a n advantage with regard t o electronics and insulation; however, it brings with i t the problems associated with low-energy ions which are easily affected by stray fields. When operating with high molecular weight samples, the unheated analyzer plates tend t o pick up static surface charge. Since the ions are of low energy, the build-up of such stray fields soon destroys the resolution. To reduce this surface charging, battery-operated heaters were installed on each plate (Figure 1). Because of the design of the mounting system, the gap between the plates contracts when the system is heated. Mounting brackets were designed so that the gap could be adjusted correctly before evacuation and heating. Furthermore, since the collector end of the plates is rigidly fixed, the expansion along the arc changes the geometry of the electrostatic field-terminating aperture a t the source end. To prevent this difficulty this aperture was mounted directly on the plates. With the field plates maintained a t 200” C., the instrument can
Table 1. Selected Doublets in HighResolution Mass Spectra
Doublets HI& Hg-D CH-C’3 CHrN CH4-0
xrco
C&-S SiCaH-, Oz-s
APPARATUS
Basically the instrument employed is a 60°, 12-inch radius unit of the coincident-field double-focusing type which has been described by Voorhies et al. (9). A schematic representation is shown in Figure 1.
CyHCl” CsH-Cl” CjH,-Ar c~H7-Br~~ CBH9-Br8’ CidHwHglQ* CiaHzr-Hg*o*
Mass Difference, AM, A.M.U. 0.0939
Resolution Required at Mass 200, 200/AM 2,130
0,0045
44; 000
0.0015
0.0126 0.0364 0.0112 0.0905 0.0034 0.0178
0.0233
1R0.000 -_.
15,900
5,500 17 ,900
2.210 59; 000
11,200
8,580
0.0420
4.770
0 1365
2: 900 1,470
0.0689 I
0.1541 0.2687 0.2032
1,300 740 990
be operated for two months or more before cleanup is necessary. The resolution obtained over the mass range 20 to 1000 is about 1 in 2000 measured a t 5% of the peak height. GENERAL CONSIDERATIONS
The exact mass of a neutral atom differs slightly from the mass number of the atom. Aston ( I ) established that the isotopic mass of Ole is not four times that of He4, He4 is not four times HI, etc. Many compilations of atomic masses have appeared in the literature, one of the most recent and complete being that of Duckworth ( 7 ) . The exact mass of a n ion of known empirical formula can be calculated from the exact masses of the constituent atoms. For example, nonane and naphthalene, both of nominal mass number 128, have calculated masses of 128.1972 and 128.1033 a.m.u. (atomic mass units), respectively. A knowledge of the exact masses, however, is of less utility than the difference between exact masses, especially of ions having identical nominal mass numbers. I n the example of nonane and naphthalene, this difference is 0.0939 a.m.u. This value, observed for overlapping hydrocarbon ions, corresponds to the difference in exact mass b e h e e n one carbon atom and 12 hydrogen atoms. The mass differences of this and other selected doublets which can appear in the high-resolution mass spectra of petroleum are shown in Table I. The great variety arises from the presence of atoms other than carbon and hydrogen. Some of the important doublets, not specifically given in Table I, can be calculated from the basic doublets. For instance, C,Ha-CO, is identical to 2(CH4-0). A fairly complete liqt of doublets commonly encountered in organic chemical rrork has recently been reported by Beynon (2). Resolution is defined in many ways. For instance, the criterion may depend upon the valley between peaks, the interference a t the center of one peak due to the other, the peak width a t onehalf peak height, etc. Beynon (2) has pointed out that the definitions of resolution do not give a realistic estimate of how close two peaks can approach before they are indistinguishable from a single peak. Much useful VOL. 32, NO. 11, OCTOBER 1960
1489
146
Figure 1. trometer
146%
147
153%
154
147%
148
14W'~
Schematic of double-focusing mass specR = 12 inches
4 = 60 degrees B = Magnetic field E = Electrostatic field plates T = Field terminating apertures F = Plate Heaters
S=
Ion Source
153
V = Accelerating voltage supply
A = Vibrating reed amplifier
qualitative information can be derived even if a peak is barely perceived to be a doublet. Several doublets-e.g., C3Hd-Ar and CI5H22-Hgz02-are familiar landmarks even in conventional single-focusing instruments. At the other extreme, some doublets of importance t o petroleum technologye.g., CH,-K, CH-C13, and S-C3H--4can be resolved only with instruments of very high resolving power as indicated in the third column of Table I. INTERPRETATION
The interpretational aspects deal with the region of petroleum spectra in which overlapping hydrocarbon types are resolved. The upper limit of this region for the instrument described is about m/e 400. At this mass hydrocarbons differing in z-number by 14 units are still sufficiently resolved to furnish much useful qualitative information. Mass Marking. The initial step is the identification of the nominal mass and z-number of each spectral peak. The nominal mass numbers are readily identified by techniques commonly used for conventional spectra. Indexing according t o z-number is less straightforward. Several hydrocarbon peaks usually can be positively identified both as to mass and z-number from previous knowledge of the sample or by the presence of doublets, which include such established landmark peaks as mercury, carbon dioxide, or argon. The peaks belonging to the same carbon number as the starting peak are identified by a divider, with its spacings set equal to the length of record equivalent to the mass of one hydrogen atom. The peak identification is made by moving the divider along the record 1490
ANALYTICAL CHEMISTRY
155
154'4
155%
MASS-TO-CHARGE R A T I O N
Figure 2. Half-mass region of high-resolution mass spectrum of catalytically cracked heavy gas oil
in the direction of increasing mass until the peak of highest z-number is reached (highest in a positive sensr). The process is repeated in the opposite direction until the lon est z-number is reached. Usually one or more hydrocarbon-overlap doublets are present which include peaks from the starting carbon number. The companion peaks are thus identified and form the starting points for indexing the neighboring carbon numbers. Mass Defect. It is convenient t o use the term "mass defect" in a new sense for the interpretation of petroleum spectra. It is defined as the difference between the exact masses of the ion in question and a reference hydrocarbon ion which has t h e same nominal mass number. The standards adopted are all hydrocarbon ions whose z-numbers ' a r e in the + 2 through -11 family. Family in this sense includes 14 consccutive z-numbers: $16 + +3, + 2 + -11, -12 + -25, etc. The + 2 -11 is chosen as the standard reference, inasmuch as the $ 2 is the highest z-number nornially observed for monoisotopic hydrocarbons. This family includes more hydrocarbons than does any other familyonly 25 masses, all below mass 60, having no hydrocarbon representatives. This system of mass defects should also prove useful in the interpretation of spectra of materials containing no carbon or hydrogen atoms, since hydrocarbons offer many advantages as mass markers. The standard mass defect is positive if the exact mass is less than that of the reference and negative if it is greater. Hydrocarbon spectra are readily interpreted by virtue of 4
the fact that all of the peaks have mass defects which are multiples of 0.0939 a.m.u. Hydrocarbon ions belonging to the + 2 -11 family have mass defects of 0.0000 a.m.u., by definition; those in the - 12 + -25, 0.0939 a.m.u., -39,0.1878 a.m.u., those in the -26 etc. Accordingly, the standard mass defect of nonane is 0.0000 a.m.u. and of naphthalene is 0.0939 a.m.u. Spectra of nonhydrocarbons are complicated by the mass defect contribution of the hetero atom or atoms. Sonhydrocarbon ions of the type produced from petroleum consist of a hydroca~bon portion, Cn(Hzni+ or (CH2)ntHZt,and a hetero portion, A, which can be one or more atoms of one or more elements. The standard mass defect of A is defined in the same way as the defect of hydrocarbon ions-Le., the difference between its exact mass and the exact mass of the reference hydrocarbon, real or fictitious, having the same nominal mass as A . (Many masses below 60 cannot be represented by real hydrocarbons.) The mass defect of the ion, (CH2)n~Hz~.4, can be calculated from the standard mass defect of A , the nominal mass number of the ion, and the value of either n' or z'. Conversely, the empirical formula of the ion can be derived from the observed mass defect, the nominal mass number of the ion, and the standard mass defect of A . The exact masses and the standard mass defects of selected nuclides are listed in Table 11. A general method of calculating the mass defect, DI,of an ion (CH2),tHz?A is as follows: Let the reference hydrocarbons of A and (CH2),~HZ,A be (CH2).H, and (CH2).H,, respectively, 4
--f
and the mass defect of '-1 be DA,nhere C, H, and A are the exact masses of carbon (12.003817 a.ni.u.), hydiogen (1.008144 a.m.u.), and the hetero moiety, A , respectively. Then:
DI
and, DI = D a
DA = (CH,),H, - d
(1)
(CHz),HS - (CHz),'H,'A
(2)
Table II.
Suclide
1 008144
10 01613 11 01281 12 003817 13 007493 14 00753 15 00488 16 000000 18 00488 19 00444 23 99267 24 99378 25 99085 26 99011 27 98582 28,98570 29.98329 30.98358 31.98224 33.97865 34. Si998 36.97759 39,97509
+ [(CHz)J% -
Hence, the mass defect, D I , of organic ions containing -4 is the sum of Da and the mass defect of a hydrocarbon representing the combination of the reference hydrocarbon of A and the hydrocarbon portion of the ion. The latter defect is a hydrocarbon defect, and, therefore, occurs as multiples of 0.0939 a.m.u., the hydrocarbon overlap. Therefore, the expression for DI may be written:
Da
+ 0.0939 [(n' +
2)
- n] (4)
50.96009 53 95873
or, its equivalent,
The standard mass defects of combinations of hetero atoms are calculated readily from the standard mass defects of the constituent atoms. For example, the hydrocarbon equivalent of SO3 is (CH2)BH--lo 3(CHZ)IH+z or (CH2)6H--4 and the mass defect is -0.0034 3(0.0364) or 0.1058 a.m.u. I n the case of S O z , the hydrocarbon equivalent calculated from the constituents is not a member of the reference 2(CHz)lH+z family-i.e., (CH2),H0 or (CH.J3Ht4. The calculated defect, 0.0126 2(0.0364) or 0.0854 a.m.u., is the mass defect rclatire to the hydrocarbon (CH&H+l. The mass defect relative to t'he reference hydroIO is 0.0939 a.m.u. carbon (CH2)4Hless, or -0.0085 a.ni.u. It should he re-emphasized here that an ion containing a hetero atom or group does not necessarily exhibit the same standard mass defect as the hetero atom 01' g1'0up. The compounds of most elements shorn the standard mass defect of the element in only a limited number of the possible ions which ma). lie formcd from them. This is true because of the mathematical considcrations which limit the instances ' y) . fcr d i i c h the term 2 - ( 214 in Equation 4a is equal to zero. For example, in the frequently encountered case of ions containing one atom of sulfur, the value of 2' is limited by valence considcrations to a maximum of + 2 . Since g = -10, the value of 2 for the reference hydrocarbon of the ion cannot lie above -8, and, by definition, cannot be less than - 11 if the ion is to
~
Bra1 I Hg202
+
5
1
1 1
1 1 1 1 1
2 2 2 2 2 2 2
2 2 3 3
3 3 3 3 4
4 4
1 4 5 0
.4.hI.U. -
0.0000
+ 1
0.0015
+ 2 - 10
-0,0652 -0,0286 -0.0171
- 4 - 3
- 2
0.0000 0.0045
- 1
0.0126 0.0234 0,0364 -0.0461 -0.03i5 0,0150 0.0220
0 + 1
+ 2 - 10 - 9 - 4 - 3
- 2 - 1
0 ,0331 0 0420 0 .054.1
0 + 1
0.0827 0.032 - 0.0128
$ 2 -11 - 10
-0.0o:H 0 Olr5 0 02:%:3 0.0420 0 . Oii80 0 079(j 0 .1Oi1 0,1277 0 . 1351 0 . 1420 0 .0(jO;% 0 09:i!i 0 1114 0 .14-18 0.161:3 0 . 13135
-
8 7 5 2 5 2 0 + 1 + 2 - 10 -
T
70.94737
5 5 5
i - 1
i8 04349
A
- - 3
80.i4213 126.94503 202 0332
6 9 15
- 5
- 1
0.1541 0.2411
- :3 + I - 8
0,2032
Taken from Ducknorth ( 7 ) .
Table 111.
+
+
0 0
Standard
Mass Ilcfect,
Y
X
5G.95351 57.95377
68.94755 Br79
Reference Hydrocarbon, (CH*)zHv
55,952i2
59.94982 62 94961 6 4 . 91843
+
+
Exact lIass,G A.M.U. 2 014741 4 00387
(CH*)n'+zHz'+vl (3)
DI
Mass Defects of Selected Nuclides
Effect of z-Number and of Type and Amount of Hetero Atoms on Mass Defect of Nonhydrocarbon Ions No. of
Hydrocarbon Overlaps, - Reference Hydrocarbon (n'- n orx) group, HeteroA, [ z - (zi4+ Y)] Ion, Ion, (CH,)nJHz'd (CH2)nHz ( CHz )zHy
+
Sominal Mass KO.
(CH?)~H-IO
( CHz ISH-i o
(CH?)?H-la ICH.),H-,n ( CH;~,H-;; (CH,)J-lo (CH,)aH-io 242 241 240 227 226
0 0 1 1 2
3 1
Standard Mass Defect, A.1I.U. A -0 -0 -0 -0 -0 -0 -0 0 0 0 0 0 0
0034
Ion
0034
-0 0034 -0 0034 0 0905
0034 0034 0034
0 1844 0 2783 0 0905
0364 0364 0364 0364
-.O ,0575
0034 0034
0364
0 0905
--0.0575
0.0364 0.0:364
0.1303 0.2252
0364 0 0364 0 0211 0 0153 0 0517
0.0964 0.0728
VOL. 32, NO. 11, OCTOBER 1960
1491
O.lO'J2 0.1456
have a mass defect equal to the standard mass defect of sulfur, This is illustrated in Table 111,where the sulfur-containing ion a t mass 241 (z’ = -1, z = -11) exhibits the standard mass defect, while the similar ion a t mass 240 (z’ = -2, z = 2) exhibits this defect plus one hydrocarbon overlap. There are also shown in Table I11 examples of ions containing one atom of oxygen. Again, valence limits the maximum value of z’ to +2, but in this case the value of y, +2, dictates a maximum value of 0 for z’ if the ion is to exhibit the standard mass defect of oxygen. Hence, the oxygen-containing ion a t mass 240 (z’ = 0, z = +2) has the standard mass defect equal to that of oxygen, while the ion a t mass 241 (2’ = +1, z = -11) exhibits the stand. ard defect minus one hydrocarbon overlap (an example of a negative hydrocarbon overlap), Other appdrent anomalies which result from the limitations on the values of the term o f z - (2’ 14 I/) are illustrated for oxygen- and sulfurcontaining ions in Table 111. The standard defects of ions containing one or more oxygen atoms a t masses 226 and 228 serve to illustrate the multiplicity of values which may be observed. This type of anomaly is general for all hetero atoms or groups except those whose nominal mass numbers are divisible by 14 (NI4, Si2g, Fe66, etc., for which y = 0). I n these cases the ions exhibit the standard mass defect of the hetero atom if the value of z‘ is in the reference family, f 2 to -11. The empirical formulas of hydrocarbon ions are readily established from the observed mass defect by the number of units of 0.0939 a.m.u., giving rise to the observed defect. The formulas of nonhydrocarbon ions are deduced by the following procedure. The observed mass defect, together with values corresponding to the observed defect plus 0.0939 a.m.u. and minus one or more units of 0.0939 a.m.u., are compared with the entries in tables of standard mass defects calculated for hetero atoms and combinations of hetero atoms likely to be encountered. Possible empirical formulas are deduced for each match found. For any particular match the formula of the hydrocarbon portion of the ion is the difference between the formulas of the reference hydrocarbons of the ion and the hetero group corrected for the number of hydrocarbon overlaps involved in the match:
ion of composition CnHZn + has an ap-
+
+
where w is the number of overlaps. The values of n and z are established by the nominal mass of the observed peak and the values of x and y by the 1492
ANALYTICAL CHEMISTRY
j
j,
C6HI0
~2
C6H13 H14 3 , CsC13H!, , C7H ‘ C 7 H 2 C7H 84 85 86 87
‘6Yl
83
MA S S-TO
- CHARGE
RAT I O
/
-
Figure 3. Selected regions from highresolution mass spectrum of platformate a. Half-mass region b. Toluene-hexane parent region
particular A for which the match occurs. Thus n‘=n -x+w Z’
=z - y
-1
4 ~
For example, a mass spectral peak a t mass number 316 has an observed mass defect of 0.109 a.m.u. A match is found for 0.109 minus 0.0939 or 0.015 a.m.u. which corresponds t o the standard mass defect of three oxygen atoms. As w is equal to 1, the empirical formula of the hydrocarbon portion is: (CH,),’Hs’
=
(CH2)23H-6
- (CH2)dH-s
+ (CHz)iH-i4 = (CHz)mH-iz
and the ion is (CH~)ZOH--~ZO~ or C20H2803
The mass defect of sulfur (0.0034 a.m.u.) is such that sulfur-containing ions cannot be resolved from hydrocarbon ions by present analytical highresolution instruments. It is possible, however, to establish the presence of sulfur in chromatographic fractions prepared from sulfur-containing stocks. The mass spectra of successive fractions exhibit apparent hydrocarbon series that are out of sequence with respect to the order of adsorption of hydrocarbons. Such series are due t o sulfur types whose mass defects correspond t o hydrocarbons in families one or more removed from those expected to be present in the fraction, The presence of sulfur-containing ions often can be verified by the relative abundance of the heavy isotope peaks. M a s s Defect of Doubly-Charged Hydrocarbon Ions. A doubly-charged
parent mass corresponding to Cn/2 Hn+ (sp),The peak will appear a t whole mass numbers if z is even and a t half-mass numbers if z is odd. If z and n are both even, the half-mass peak cannot be distinguished from the peak of the singly-charged ion of one half the mass. For example, doubly-charged naphthalene, CIOHO,and singly-charged CsHd ions result in superimposed peaks. If z is even and n is odd, however, the apparent exact mass lies midway between the exact masses of singlycharged ions on the (z/2)+7 and ( 4 2 ) -7 series. Doubly-charged ions of odd carbon number are thus displaced 0.0470 a.m.u. from singly and doublycharged ions of even carbon number. This is illustrated in Figure 2, which shows the partial spectrum of a heavy gas oil from catalytic cracking. APPLICATIONS
The applications are concerned primarily with the mass region below m/e 400, the mass limit a t which useful resolution of hydrocarbon doublets can be effected with our instrument. Pure Compounds. A number of pure hydrocarbons of low molecular weight have been studied. As expected, only a few doublets are present and all of these can be accounted for by impurities such as argon, oxygen, carbon dioxide, etc. The characteristics of the spectra of low-boiling saturates and aromatics are all in the spectrum of a stabilized platformate prepared from a C6/C7 feed stock. Selected regions of such a spectrum are shown in Figure 3. The following points are of interest: CsH4-argon doublet at m/e 40 CiHi CJY3H7 - 7- COZ triplet at a m/e 44 Half-mass peaks of carbon numbers C6 and C7 illustrating the displacement of the odd-carbon ions Metastable peak a t m/e 41. This metastable peak apparently corresponds t o the transition, 43 42. I n conventional spectra metastable peaks resulting from the loss of one or three hydrogen atoms are very rare ( 5 ) The extent to which hydrogen is stripped from the benzene ring
-
High molecular weight pure compounds have been studied in order to guide instrumental operation and to elucidate fragmentation modes. Perfluorotriisobutylamine, because of its high volatility coupled with high molecular weight, is ideal for testing instrumental behavior. A portion of its spectrum is shown in Figure 44. The parent peak region of a blend of 2-nhexyldibenzothiophene, 2-n-decylnaphthalene, and n-C,o is shown in Figure 4,b. The components have mass num-
I
CARBON NUMBER n
1
1
1
564
1
1
1
1
1
1
1
1
1
MASS-TO-CHARGE
268
1
1
576 577
570 RATIO
+
2 70
269 MASS-TO-CHARGE
RATIO
Figure 4. Partial high-resolution mass spectra of highmolecular-weight compounds a.
b.
Perfluorotriisobutylamine Blend of pure compounds of nominal mass 268
bers of 268 but differ in exact mass; their mass defects (measured from the exact mass of n-Cl,) are 0.1845, 0.0939, and 0.0000 a.m.u., respectively. Peaks a t mle 269, 270, and 271 result from heavy isotopes, primarily those of carbon and sulfur. The spectrum of 2-n-hexyldibenzothiophene illustrates the usefulness of high resolution spectra for studying fragmentation modes. For example, the loss of a neutral fragment of mass 45 from the parent ion might occur by the cleavage of the sulfur atom plus a hydrogen atom and a carbon atom from the ring. The observed mass defect of the m/e 223 ion, however, is 0.18 a.m.u., indicating that the sulfur atom is present. Actually, the sulfur atom is retained in all significant ions of mass equal to the nucleus, m/e 184, or higher. Carbon Number Distribution of Sulfur Types. I n conventional mass spectrometry it is necessary to deduce the carbon number distribution of two overlapping types. I n some spectra this is facilitated by the presence of
p
Figure 5. Distribution of overlapping types in high-resolution mass spectrum of polyarom,atics from West Texas straight-run residue Observed mass defects of ions of 1 reference z-number 0 0.09 a.m.u. (C,H2,-d 0 0.1 8 a.m.u. (C,H2,-2,)
two maxima. If not, the two distributions cannot be distinguished. High-resolution spectra supply the two distributions directly. An example is shown in Figure 5 for a set of doublets on the +1 reference z-number series. The data are taken from the spectrum of a polyaromatic concentrate recovered from a West Texas straightrun residue. As this fraction is relatively narrow in type, the principal doublets are due not to overlapping hydrocarbon types but to the presence of sulfurcontaining ions. The peaks on the z = -27 series are ascribed to dibenzothiophene fragments. Two maxima appear in the distribution of the z = -13 peaks, one a t Clz and a second a t about C17. The second maximum was not anticipated on the basis of conventional spectra. The first maximum in this series isascribed tonaphthalene fragments and the second is tentatively ascribed to dicyclic sulfides, Cn’Han)- 3 S. The mass defect of the latter differs from hydrocarbons on the - 13 series by
9
(FRAGMENT)
210
212
214 216 218 220 MASS -TO- C H AR G E RAT IO
222
224
Figure 6. Partial high-resolution mass spectrum of a West Texas monoaromatic concentrate showing presence of thiophenes VOL. 32, NO. 1 1 , OCTOBER 1960
1493
only 0.0034 a.m.u. Thiabicycloalkanes are known to be present in some crude oils-e.g., in Agha Jari kerosine (4). Another possibility for the second maximum is tricycloalkyl benzenes which have mass defects identical t o naphthalenes. Evidence for Thiophenes in Virgin Gas Oil. Alkylthiophenes boiling in the gasoline and kerosine range have been shown definitely t o be present in some crude oils (3, 8 ) and indirect evidence from conventional mass spectrometry points to their presence in some light gas oils. Evidence is shown in Figure 6 for their presence in a monoaromatic fraction recovered by chromatography and distillation from the light gas oil region of West Texas crude oil. The peaks a t m/e 210 and 224 have a mass defect of 0.09 a.m.u. and are assigned to alkylthiophenes having, respectively, nine and 10 carbon atoms in side chains. Cycloalkylthiophenes appear to be present also but in lesser amount. rllthough the present instrument cannot resolve thiophenes from C,H?, - 14 hydrocarbons. the latter are absent as indicated by the very IOU alkylnaphthalene peak a t m/e 212. Cycloalkylnaphthalenes are expected to be preseiit in considerably lower concentration than alkylnaphthalenes in this fraction. Tri- and tetracyclic sulfides, if present, would not be distinguished by mass defect from alkyl and cycloalkylthiophenes. Sulfides, however, are not expected to appear in monoaromatic fractions prepared by chromatography. Nonhydrocarbon Components in Catalytic Cracking Streams from West Texas Gas Oil. The sulfur and oxygen types in the feed and products from the catalytic cracking of West Texas gas oil have been studied by highresolution mass spectrometry. Benzothiophenes appear on t h e -20 series (mass defect of 0.09 a.m.u. a t -6 reference z-number) and dibenzothiophenes on t h e -26 series (mass defect of 0.18 a.m.u. a t +2 reference z-number) in the spectra of fractions pwpared from both feed and product. -4small amount of material on the -40 series starting a t m/e 240 appeals out of sequence in the spectrum of heavy gas oil. If the ions responsible contain only one sulfur atom, the empirical formula n ould be C,H2, - 28s and the mass of the nucleus peak would he considerably larger than m/e 240. Condensed systems of t\vo benzene rings and two thiophme rings, such as
resolved peaks on the -14 and -15 series beginning with mass 168. It is suggested that these result from dibenzofurans,
\
s/-v
Other
‘
fit the mass defect and nucleus peak 1equirements. In the spectra of polyaromatic concentrates, oxygen-containing ions a1e evidvnt i t i’ ~ i i ; o i i r i t a4 pattially
oq:q
comparative amounts of the various hydrocarbon types based on the total ion intensity of the ions in the parent region. Both waxes contain about the same n-alkane content. Was 2 contains more isoalkanes and wax 1 more cycloalkanes and aromatics.
(1) Aston, F. R., “Mass Spectra’of Iso-
topes,” Edward Arnold and Co., London, 1933.
( 2 ) Beynon, J. H., “Advances in Mass
Spectrometry,” J. D. M‘aldron, ed.,
p. 328, Pergamon Press, London, 1959. (3) Birch, S. F., J . Inst. Petrol. 39, 185
(1953).
( 4 ) Birch, S. F., Collum, T. V., Dean,
R . A., Denyer, R. L., Ind. Eny. Chem. 47,240 (1955). ( 5 ) Bloom, E. G., Mohler, F. L., Lengel, J. H., Wise, C. E., J . Research ~Vutl. Bur. Standards 40, 437 (1948). (6) Craig, R. D., Errock, G. A;, “hdvances in hfass Spectrometry, J. D. FValdron, ed., p. 66, Pergamon Press, London, 1959. (7) Duckworth, H. E., ‘.Mass Spectroscopy,” Cambridge University Press, London, 1958. (8) Thompson, C. J., Coleman, H. J., Mikltelsen, L., Yee, D., Ward, C. C., Rall, H. T., A s . 4 ~ . CHEM. 28, 1384 (1956). (9) Voorhies, H. G., Robinson, C. F.,
Hall, L. G., Brubaker, W. M., Berry, C. E., “Advances in Mass Spectrometry,” J. D. Waldron, ed., p. 44, Pergamon Press, London, 1959.
RECEIVED for reviey December 24, 1959. Accepted June 6, 1960. Presented at the meeting of Committee E-14 on Mass Spectrometry of the .Imerican Society for Testing lfaterials, Los Angeles, Calif., 31ay 17-23, 1959.
~
~
