ANALYTICAL CHEMISTRY
430 trations for this paper were 1 square inch in cross section; columns 2 and 4 inches square have been made without difficulty. When shaved with a knife, these columns show no evidence of nonuniformity in packing. By use of the capillary-ascent method of solvent travel combined with the rigid characteristics of the column, it is a matter of small concern to transfer the bar from one solvent to another. A preliminary examination of the position of the bands can be made by spraying an appropriate reagent on the column, scraping the reagent off the sides, and then returning the bar t o that solvent or a new solvent combination for further development. This is a distinct advantage over a packed chromatographic column, where further development is impossible once the column has been removed from the glass tube. Although conventional chromatographic borosilicate glass tubes can be used for fluorescent chromatography with the longer wave-length ultraviolet light, the shorter rays (230 to 290 mp) needed for excitation of the zinc silicate are absorbed by this glass. Therefore, this method is particularly adaptable to the use of the ability of compounds to absorb ultraviolet light, because columns made fluorescent with zinc cadmium sulfide and zinc silicate can be observed without being removed from the solvent and without interference due to absorption of the short wave-length ultraviolet light by a glass envelope. A number of developed columns have been examined for uniformity of the bands through the interior of the column. Successive small layers have been removed from the surface and the new surface examined by spraying or by observation in ultraviolet light. The zones have been found t o be uniform throughout the cross section of the column. The zones have been more uniform
than have the zones of columns packed in glass, because the solvent in these columns tends to travel more rapidly along the glass surfaces than through the adsorbent. Occasionally a column will crack in a direction perpendicular to the supporting glass rod during the drying period. This defect can be remedied by gently pressing the bar together; columns with such cracks have been used without any effect on the movement of solvent or compounds. Round bars have been made with thin plastic casings as molds; however, the square bars are more convenient for applying colordeveloping reagents by means of sprays. Solvents containing water have been used to develop columns; although they impart fragility to the column, such columns can be successfully handled. These columns can he accurately cut with a coping saw and areas of interest removed and extracted with suitable solvents. ACKNOWLEDGMENT
The authors are particularly grateful to George J. Keller of this laboratory for the preparation of the drawing of Figure 1. LITERATURE CITED (1) Kirchner, J. G.. Miller, J. M., and Keller, G. J., . 4 ~ . 4 ~Cmmf., . 23, 420 (1951). (2) Mitchell, H. K., and Haskins, F. A., Science, 110, 278 (1949). (3) Sease, J. W., J . Am. Chem. Soc., 70, 3630 (1948). (4) Zechmeister, L., Cholnoky. L., and Ujhelyi, E., Bull. soc. chim. hiol., 18, 1886 (1936). RECEIVED July 7, 1950. Presented before the Division of Analytical CheniSOCIETY, Chicago, istry a t the 119th Meeting of t h e AMERICAXCHEMICAL Ill. Report of a study made under the Research and Marketing Act of 1946.
Compound Types in Gasoline by Mass Spectrometer R . A . BROWN, The Atlantic Refining Co., Philadelphia, P a .
A
NUMBER of laboratories throughout this country use commercial model mass spectrometers to obtain high precision analyses on a wide variety of organic compound mixtures (6, 7 , 10, 12, 14). Notable success has been achieved in the field of hydrocarbon analysis, where very small samples containing up to thirty components can be analyzed in 1 or 2 man-hours (2, 3, 16). In view of the speed, accuracy, and small sample requirements of these methods it appeared highly desirable to extend the scope of the mass spectrometer to compound-type analysis of complex liquid hydrocarbon mixtures such as gasolines. A study of this possibility has resulted in a quick and accurate spectrometric method, which appears to be a worth-whjle addition to numerous other procedures previously described (6, 8, 9, 11, 15). This method has been applied .to some 500 samples, and the resulting data have been used to evaluate laboratory and pilot plant products, commercial grade gasolines, and solvents over a period of 2 years. Analytical data are obtained on total paraffins, total cycloparaffins and/or mono-olehs, aromatics, and the group designated as the “coda” type-namely, cyclomono-olefins, diolefins, and acetylenes. Calculation of aromatics with unsaturated side chains has not been evaluated here, although their concentration is easily estimated. Pl’ormally such compounds are absent but, if present, appear in relatively small and constant amounts. I n the case of eome catalytically cracked gasolines, for instance, such compounds constitute 6% of all aromatics. This method reports the calculation of total aromatics only, although average sensitivity data and 10 minutes’ additional cal-
culation time are all that is needed to resolve aromatics according to molecular weight. Mono-olefins are differentiated from cycloparaffins by an auxiliary procedure, such as bromine number or nitrosation (1). Accuracy achieved is found to be *l% for aromatics and *2% for “coda” compounds in all types of mixtures. Other components are determined within *2oJ, in wide boiling mixtures but only within *4y0 in mixtures of 15” C. or less range. Calibration data presented here can probably be used directly by other
Table I. of Carbon .4toms
Numerical Summary of Compounds Studied
ATO.
4 5 6 7
8
9 10 11 12 13 14 15 16
Total
Aliphatic paraffins 2 3 5 9
18 10 1 0 1 1 1 0 2 53
Kumher of Isomers Studied CycloAliphatic olefine, Cyclomonodienes, Aroparaffins olefins acetylenes matics .. 3 2 .. 5 3 .. 1 2 1 2 11 2 1 7 3 5 2 4 21 2 .. 8 4 14 1 4 0 .. 1 0 .. 1 0 2 0 0 1 1 .. .. .. 0 .. .. .. 1 34 11 34 40 Total = 172 . I
V O L U M E 23, NO. 3, M A R C H 1 9 5 1
431 pounds numerically summarized in Table I. The list includes most of the C&S paraffins, aromatics through Cots, and a number of higher molecular weight and olefinic compounds. Comparison of the various spectra showed that ions which appear a t m / e + ratios 43, 57, 71, 85, and 99 were generally most abundant in paraffins. Similarly, relatively large peaks at 41, 55, 69, 83, and 97 appeared to be characteristic of cycloparaffins and mono-olefins, whereas ions a t masses 67, 68, 81, 82, 95, and 96 are contributed generally by cyclo-olefins, diolefins, and acetylenes. Aromatic fragments were found at m/e+ values of 77, 78, 79, 91, 92, 105, 106, 119, 120, 133, and 134. When the peaks in each group listed above are mathematically combined and treated as one, it is found that pattern coefficients of combined peaks are similar for compounds of the same type
The determination of compound types in gasoline fractions has been the object of considerable attention by petroleum chemists during the past 25 years. Numerous methods have been developed based on chemical reactions and physical constant data which are, in general, characterized by the need for skilled analysts and rather time-consuming laboratory measurements. In view of the frequently demonstrated ability of instrumental analysis to accomplish what conventional methods cannot, mass spectral data were studied to determine if such data properly used could supplant or supplement other methods of type analysis. Results of the study consist of a mass spectrometric method which is quick and reasonably accurate, and requires only 0.001 ml. of sample. Hydrocarbon types are determined, except for cycloparaffins and monoolefins which are grouped. These latter compounds may then be resolved by chemical analysis, such as nitrosation or bromination. The method can probably be used directly by other mass spectrometer users. In addition, its principle can be extended to obtain type analysis of higher boiling petroleum fractions and mixtures of nonhydrocarbon compounds.
Table 11. .\lass Spectra Patterns of Some Aliphatic Paraffins KO.
of Carbon Atoms
5 5 5
METHOD OF ANALYSIS
The applicability of the mass spectrometer to type analysis was determined by a study of mass spectra for the C,-Cl0 com-
6 6 6 6 6
8
8 8 8 8
8 8 8 8
ROJEOT N0.44 0 Y W D K f
B. N-nrXANr(sERWL
N0.147lSU0UITTLO TO A R I . RE¶EARCH PROJECT NO 4 4 0 1 HOUDRY PROCESS
0 e-YETHYLPENTANEISERIAL NO,IO)SU0YITTEDXI & P I RESEARCH PROJECT UO 4 4 BY BUREAU OF
I
D.U-HEXANE I¶ERIAL NO.9lSUBYITTED TO b e l . RESEARCH PROJECT NO. 4 4 BY BUREAU OF STANDARDS
16
eb
3b
4b
sb
66
7b
sb
$0
160 iio iio i i o
140
do
SENSITIVITY OF N-BUTANE AT MASS 4 3
Figure 1. Sensitivity of 243 in Mass Spectra of %-Methylpentane and n-Hexane 2-Methylpentane Without temperature control With temperature control n-Hexane A Without temperature control 0 With temperature control
Isobutane n-Butane Av. Isopentane n-Pentane Neopentane Av. n-Hexane 2-hfethylpentane 3-Methylpentane 2,2-Dimethylbutane 2,3-Dimethylbutane
.4v. 7 7 7 7 7 7 7 7 7
8 8 8
o
2411 243
% 4 4
mass spectrometer users as, in general, these data agree well with those published under A.P.I. Research Project No. 44 (see Figure 1). Extension of this method to kerosene and furnace oil fractions has been limited chiefly by the difficulty of obtaining a representative vapor phase sample. It is possible that this could be overcome, however, by the use of a heated inlet system.
0
Compound
n-Heptane 2-Methylhexane 3-Methylhexane 3-Ethylpentane 22-Dimethylpentane 2,3-Dimethylpentane 2,4-Dimethylpentane 3,3-Dimethylpentane 2,2,3-Trimethylbutane Av. n-Octane 2-Methylheptane 3-hlethylheptane 4-hfsthylheptane 3 Ethylhexane 2.2-Dimethvihexane
tane 8 2,2,4-Trimethvloen_ . tane 8 2,3,3-Trimethylpentane 2,3,4-Trimethylpen8 tane 8 2,2,3,3-Tetramethylbutane 8 2-Methyl-3-ethylpentane 8 3-Methyl-3-ethylpentane Av. n-Nonane 9 9 3,3-Diethylpentane 9 2,2,3-Trimethylhexane 9 2,2,4-Trimethylhexane 9 2,2.5-Trimethylhexane 2,3.3-Trimethylhexane 9 3,3,4-Trimethylhexane 9 2.2.3.3-Tetramethvl9 pentane 2,2,3,4-Tetramethyl9 pentane 2,3,3,4-Tetramethyl9 pentane Av. 10 n-Decane 10 Hydrogenated triisobutylene 16 n-Hexadecane i z I i 4 n-Paraffins 15-17 n-Paraffins
253/ 243
267/ 243
277/ 243
2691 271
% .,
..
%
%
%
..
.. .. 0 0 0 0 0.04 0.02 0.06 0.01 0.03 0.03 0.05 0.08 0.06 0.06 0.05 0.08 0.05 0.07 0.07 0.06 0.08 0.17 0.13 0.12 0.14 0.20 0.21 0.14 0.05 0.12
37.0 29.0 33.0 46.5 38.0 36.7 40.4 41.5 27.5 51.0 25.5 31.8 35.5 31.0 25.0 30.0 27.5 24.0 38.0 25.0 18.1 31.0 27.7 24.8 25.3 25.5 24.2 22.5 23.5 28.0 22.7 23.6 18.8 34.0
2.2
1.2 1.7 1.7 1.6 1.3 1.4 1.6 1.4 1.7 1.5 1.7 1.3 1.4 1.4 2.0
0.22 0.09 0 0.16 0.10 0.16 0.18 0.14 0.25 0.17 0.14 0.17 0.24 0.32 0.24 0.33 0.31 0.26 0.43 0.27 0.23 0.34 0.33 0.37 0.43 0.48 0.62 0.43 0.11 0.48 0.55
0.26
3.3 10.0 0 6.7 6.6 2.0 9.0 0.90 3.5 4.4 1.7 2.4 2.1 1.9 4.7 5.1 13.0 1.5 9.5 4.7 2.5 4.7 5.3 3.0 6.4 12.5 3.3 6.8 3.8 4.2 8.2
29.5
1.8
0.59
0.20
24.0
25.0
1.3
0.73
0.26
19.0
22.0
1.6
0.56
0.14
5.2
23.0
1.6
0.52
0.15
2.5
24.7
2.4
0.71
0.18
24.3
28.9
1.8
0.63
0.16
7.7
18.5 24.7 24.0 27.0 25.2 20.0 22.0 26.2 27.8
1.7 1.6 1.4 2.1 1.7 1.5 1.4 1.4 1.8
0.48 0.48 0.32 1.0 0.66 0.46 0.33 0.63 0.70
0.08 0.16 0.13 0.20 0.06 0.13 0.16 0.40 0.40
8.5 8.4 5.0 23.0 14.6 6.0 7.5 17.8 5.7
22.0
1.5
0.61
0.15
9.0
24.5
1.6
0.67
0.15
18.0
26.5 23.7 24.2
1.4 1.6 1.6
0.69 0.58 0.54
0.15 0.16 0.08
24.5 13.3 7.4
24.3 29.8 27.1 26.9
1.0 2.2
0.90 2.4 2.4 2.6
0.19 3.0 0.30 0.41
30.7 17.9 15.4 16.1
,.
1.5 1.0 1.4 1.3 1.5 1.3 2.5 1.7 1.8 1.8 1.3 1.4 1.7 1.9 1.4
1.5 1.5
ANALYTICAL CHEMISTRY
432 Table 111.
Mass Spectra Patterns of Some Cycloparaffins
XO.
of Carbon Atoms
Compound
243/ 241
% 5 6
6
7 7 7 7 7
8 8
8
8
8 8 8 8 8 8
8 8 8
9 9 9 9
10 10 10 IO 14
9.2 Cyclopentane Methylcyclopentane 14.8 Cyclohexane 18.8 Av. 16.8 Methylcyclohexane 5.7 Ethylcyclopentane 7.8 1,l-Dimethylcyclo11.2 pentane cis-1.2-Dimethylcy1.5. 1 clopentane trans-1,Z-Dirnethyl16.4 cyclopentane cis-1,3-Dimethylcy14.4 clopentane 1rans-1,3-Dimethylcy15.8 clopentane 12.3 Av. 1.1-Diniethylcyclohexane 16.4 czs-1.2-Dimethylcy12.7 clohexane trans-1,2-Dimethslcs15.0 clohexane cis-1,3-Dimethylcy12.9 clohexane 1rans-1,3-Dimethylcy9.7 clohexane cis-1,4-Dimethyley11.4 clohexane trans-1,4-Dimethylcr10.9 clohexane 1-Methyl-1-ethyl cy5.6 clopentane cis-1-Methyl-2-ethyl 12.5 cyclopentane trans-1-Methyl-%ethyl 12 8 cyclopentane cis-1-Methyl-3-ethyl 13.9 cyclopentane trans-1-Methyl-3-ethyl 11.9 cyclopentane Isopropylcyelopentane 1 9 . 5 14.4 n-Propylcyclopentane lI1,2-Trimethylcyclo24.3 pentane 1,1,3-Trimethylcyclo26.2 pentane c i s , c i a ,cis-1,2,3, Trimethylcyclopen20.0 tans cis,cis,trans-1,2,3-Trimethylcyclopentane 22.4 czs,trans,cis-1,2,3-Tri24.0 rnethylcyclopentane ezs,cis,trans-1,2,4-Tri16.2 methylcyclopentane ~is.trans.cis-1,2,4-Trimethylcyclopentane 1 5 . 8 15.6 Av. 23.0 Isobutylcyclopentane 8.2 Isopropyleyelohexane 5.6 n-Propylcyclohexane 1,1,3-Trimethylcyclo13.7 hemne trans-Butylcyclohexane sec-Butylcyclohexane Isobutylcyclohexane n-Butylcyclohexane p-Di-tcrt-butylcyclohexane
z53/ 241
267/ 241
2771 241
2711 269
%
%
%
%
4.6 6.7 9.5 7.0 4.9 5.8
3.5 6.0 4.4 5.2 12.3 36.7
0 0.60 1.1 0.90
148 3.6 17.8 10.7 4.1 4.1
4.3
5.0
0 60
6.6
7.7
4.3
1.1
15.6
12. A
0.70 0 .,60
7.8
3.1
1.0
6.4
4.8
0.90
9.9
6.6 6.2
5.1 10.5
1.1 0.90
12.1 9.3
tween molecular weight groups, average coefficients have been calculated corresponding with CSto Ce hydrocarbons 88 shown in Table VII. These are values estimated on the basis that mixtures of a given molecular weight consist of molecules, approximately 80% of which correspond to the measured molecular weight and 20% are divided between the next lower and higher homologs. Thus Cs coefficients are weighted as 10% GIs, 80% Cs's, and 10% Cg's. This scheme has been found adequate for both narrow and wide boiling mixtures, although it is less suitable for the latter type of mixture. Coefficients are essentially independent of filament and operating conditions; only in the case of 241,243 paraffin patterns was any effect noticed. Here a 7% change occurred when the magnet current w m changed from 0.56 to 0.70 ampwe.
Table I\'.
Mass Spectra Patterns of Some Mono-olefins
NO.
of
Carbon Atoms
4.9
10.1
I 2
0.60
5 6
10.8
1.1
3.8
5 .7
10.9
1.1
2.9
4.9
10.3
1.5
2.5
5.3
10.2
2.3
2.1
5.9
12.3
1.4
1.8
.5
5.4
10.5
1.2
1.;
5 5
3.6
16.5
0 80
3.1
5
5.5
13.3
1.1
6.4
5.0
14.9
1.0
6 8
4.3
20.5
0.90
7.4
6
4.3
20.0 58.9 34.2
0.90 1.0 0.90
5.6 1.1
6
4.2 5.6
4.4
5.1
5.5
1.2
3.7
4.3
4
4 4
5
6 6
6
6
6 6 6
6.6
1.6
6.4
3.8
0.80
49.3
5.8
4.0
1.3
40.5
6.1
4.9
1.3
22 5
5 ,6
5.5
1.3
30.5
5.4 5.2 4.9 6.5 5.7
5.4 13.8 33.2 40.1 34.8
1.2 1.2 1.3 1.3 1.0
21.3 10.4 2.1 0.40 0.90
8 8 8 8
3.9
6.9
1.6
2 4
8
94.7 9.1 13.7 7.1
9.8 6.6
34.4
a.5
9
r7.J
32.5 37.0
1.6 1.4 1.3
6.7 0.80 0.80
153.0
6.0
35.2
4.5
0 90
6 6
I
4.
45.0
7
Isobutene 1-Butene 2-Butene Av. 1-Pentene 2-Pentene 2-Methyl-1-butene 2-Methyl-2-butene 3-Methyl-1-butene AV. 1-Hexene trans-2-Hexene trans-3-Hexene 2.3-Dimethyl-1-bu. tene 3,3-Dimethvl-l-butene 2-Methyl-1-pentene 2-Methyl-2-pentene 3-Methyl-1-pentene cis-3-Methyl-2-pentene 4-Methyl-1-pentsne czs-4-Methyl-2-pentene Av. 1-Heptene 4,4-Dimetliyl-l-pentene 2,3,3-Trimethyl-lbutene AV.
n 10
1.2
12 12
12.4
14
16 a
but show marked differences for dissimilar compounds. Furthermore, sensitivities of these peaks are found to be directly related t o molecular weight. These properties make it possible, then, t o consider complex mixtures as consisting of only four components which may be resolved with four simultaneous equations. Similarity of pattern coefficients for compounds of the same type is demonstrated in Tables I1 to VI, inclusive. Paraffin coefficients in Table I1 are based on either 243 or 271, where 243 denotes the sum of peaks a t masses 43, 57, 71, and 85 and 271 the sum of 71, 85, and 99. (Other sigma values shown in the tables are d e h e d in Table VII.) These patterns are essentially the same, although a slight shift occurs with an increase in the number of carbon atoms in a molecule, and this same obserration applies to other compound types listed in Tables I11 to VI. To compensate for the pattern difference which exists be-
Compound
1-Octene 2-Octene trans-4-Octene ?,4,4-Trimethyl-lpentene 2,4,4-Trimethyl-2pentene 1-Nonene Nonenes 1-Decene 1-Dodecene Triisobutylene 1-Tetradecene 1-Hexadecene
Not included in average.
n43
241
533. z-11
%
%
1.9
fi.2
1.6 1.9 1.8 5.0 3.3 3.3 3.9 4.4
4.0 37 0 9 2 9 8
6.5 9 2
7.3 .5 8 7 8 8.4 9.2 8 8 8.0 7.6 9.5 7.8
357,'
n4 1
277' Z41
%
7
0 0 0 0
0 0 0 0
1.5 1.6
0 0 0 0
X71 269
4
% 0 0 0 0
2.4
0 38 0.44 0.39
100 91 5 68 0 80 0 63 0 80.5 11 s 0 40 8 1
1.4
2.6 0.80 1.6 1.2 2.0
0 0
5.4
5
R
3.3
0.39
2 I
6 4
4.7 7.2 4 7
8.2
1 5 2.4 3.2 1 6
0.08 0.33 0.40 0.16
1 5 5 8 .5 8 '2 8
8.0 5.0
4.0 3.1
0.40
3.4
0.60
5.6
4.6
9.4
9.4 4.8 5.2
108"
1 8 10.7
6 6
3.6 2.1
0.34 0.32
'2 1 4.6
24.0
8 4
3.8
0.3fi
10 5
:1 7
2.9
0.57
'2 8
3.0
0.44 0.46 0 43 0.90 1 2
2.1
7.6 8.3 6.6
2.8 3.2 6.1 7.6 5.8
6 2
3.5
1.7
0.50
7.1 8 4 4 9 8 7 7 9 6 5
6.4
4.3
8.0 7.5 11.2 14.8 13.4 18.3 17.0
0.54
0.15 14.3 11 5 15.8
113" 11.i 17 9 58 0 29.6 11 8 1R.j
25.0 66,O
25.0 62.2 65.7 240 72.3 82. I
,5 10
7.3 12.5 (eatd.)
2.4 1.0 0.30 4.7 2.0 13.i
5.1 18 0 18 9
8 3
24.2
2.5
p6.l .31.7
.4nalysis of a sample requires accurate sensitivity in addition to pattern coefficient data. Because it is not feasible to run a large number of calibrations with each unknown sample it a p peared necessary to relate sensitivities with a standard such as nbutane. A study of this possibility showed combined peak sensitivities to be directly related to that of n-butane at mass 43 irrespective of filament and operating conditions. Figure 1, for instance, shows the sensitivity of 243 for n-hexane and 2methylpentane observed for twelve different filaments. Similar plots for as many compounds as possible were used to obtain the average curves in Figures 2 to 8, inclusive, which show that sensitivities vary directly with molecular weight. These curves and daily n-butane sensitivities are used in computing mixtures.
V O L U M E 23, NO. 3, M A R C H 1 9 5 1 Table 1'.
433 mercury-sealed sintered disks ( 1 3 ) and Teflon cutoff valves. This modification minimized hydrocarbon sorption in the inlet system and made possible the analysis of normally liquid hydrocarbons found in the gasoline boiling range.
Mass Spectra Patterns of Some Aromatics
so. Of
Carbon Atoms 6
7 8
y77
2431 277
253/ 277
267' 277
269/ 277
%
%
%
%
%
%
0 0.06 0.05 0.04 0.04 0.03 0 20 0 20 0 20 0.08 0.08 0.08
0 0.01 0 0 0 0 0.09 0.07 0.04 0.02 0.03 0.04
0 0.34 0.08 0.09 0.09 0.06 0.05 0.04 0 03 0.01 0.03 0.08 0.02 0.02 0.10 0.10 0.10 0.09 0.10 0.10 0.06
241,'
Compound
Benzene 0.04 Toluene 1.18 1.2-Dimethylbenzene 1.17 1.3-Diniethylbenzene 1.19 1.02 1.4-Dimethylbenzene Ethylbeneene 1.0 1.2,3-Trimethylbenzene 2 2 1,2,4-Trimethylbenzene 2.3 1.3.5-Trimethylbenzene 2 2 1-Methyl-2-ethylbenzene 1.3 1-Methyl-3-ethylbenzene 1.4 1.3 1-Methyl-4-ethylbenz~ne 1 1 Isopropylhenzene n-Propylhenzene 1.6 1.3-Dinirthyl-3-et hyltreiizenc 3 7 1 .2-Diinrthyl-~-erhslt~en~eiie 3 . 5 3.4 1.~-Di:neth.l-'-etiiJ.Ibenzene 1 . : ~ - D i : n e t h ~ l - - l - ~ t l i ~ I b e n z e n3c. 4 1,3-Dirnethsl-5-ethylbenzene 3 . 5 3.5 1,4-Dirnethyl-Z-ethylbenzene 3.0 1.2-Dietbylbenzene 3.0 1,3-Diethylbenzene 1,4-Diethylbenaene z.7 l-Methyl-4-isoprop).lbenznne 0.3 n-Bntvlhenzpnp 2.5 5.1 2.2 10.0 8.0 1,2-Diisopropylbenzene 6.7 1,3-Diisopropylbensene 6.3 1,4-IXisopropylbenzene
0 1.4 0.19 0.18 0.22 0.19 0.50 0.40 0.30 0.30 0.30 0.30 0.30 0.12 0.50 0.50 0.50 0.40 0.40 0.50 0.47 0.45 0.35 0.92 0.28 7.3 0.10 0.75 3.5 11.2 8.1
0.70 0.70 1.9 2.0 2.2 0.86 2.2 2.2 2.2 1.5 1.6 1.5 1.0 0.4i 1.9 1.9 1.8 1.8 2.0 1.9 1.3 1.3 1.2 1.4 0.51 0.49 0.73 0.80 1.2 1.1 1.1
271/ 277
PROCEDURE AND CALCULATION
A sample to be analyzed is first stripped of C, and lighter compounds in a low temperature dis9 tillation column to minimize sampling errors, which 9 occur on introduction of liquids containing volatile !) Y compounds to the mass spectrometer. The dis4 ., N ~ . Aliphatic , carbon ~ ~ ~ ~ Paraffins ~ Known“ 11,s. .Itoms 82.2 77.8 6 85.5 81.9 6 81.6 75.6 6 69.6 72.9 1 6 2.2 3.4 6.5 73.6 69.9 98.5 7 100 7 77.4 75.0 68.6 7 61.5 66.5 65.2 7 45.1 44.5 7.5 7.2 1.4 7.5 20.5 23.8 7.5 43.9 45.9 7.5 51.1 54.3 7.5 13.7 9.2 8 65.9 65.8 8 31.4 26.1 8 62.8 63.7 8 75.6 68.3 8
CycloparaffinKno>vna M.S. 8.8 12.5 9.8 13.4 19.8 13.9 26.9 30.2 94.1 93.7 24.4 28.1 1.5 0.0 22.6 24.9 31.4 38.5 22.5 23.2 17.0 16.8 98.6 92.8 15.8 14.5 37.4 36.1 40.6 43.8 90.8 86.3 34.2 34.1 73.9 68.6 37.1 36.3 24.4 31.7
AromaticsKnown= AT S. 9.0 9.7 4.7 4.7 4.6 4.6 0.2 0.2 3.7 2.9 2.0 2 0 0.0 0.0 0.0 0.1 0.0 0.0 11.6 11.0 37.9 38.5 0.0 0.0 61.7 63.7 18.0 18.7 5,l 5.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.0 0.0
a Known composition determined by complete resolution of compounds in mixture.
_
_
_
_
~
_
~
~
SOURCES OF ERROR
0
S E N S I T I V I T Y OF N - B U T A N E AT M A S S
Figure 5.
43
Sensitivity of 269 in Mass Spectra of Cycloparaffins
Deviation in the sensitivities and pattern coefficients of compounds with the same molecular weight is a major source of error. Such errors are most marked in the case of narrow boiling mixtures, because, otherwise, cancellation of errors takes place due t o the presence of a large number of compounds. Data in Table S I of sensitivity deviations for C4-Cs paraffins show that the sensitivities of most compounds are of the same order of magnitude, although exceptions to this rule occur a t 271 for n-hexane, 2,4dimethylpentane, Smethylpentane, 2,2,Strimethylpentane, and 2,2,4trimethylpentane and at 269 for the propyl and triniethylcyclopentanes. Pattern coefficients are essentially constant except for 4-methyl-l-pentene, 2,4,4-trimethyl-l-pentene (Table IV), coda compounds in general, and the 267/241 pa& terns observed for cycloparaffins (Table 111). Because this last pattern is vital for an accurate analysis of coda compounds, the presence of cycloparaffins reduces the accuracy of this determination.
WITH O R WITHOUT TEMPERATURE CONTROL lONIZlNQ VOLTAQE. 50 OR 70 VOLTS
MAQNETIO CURRENT. O x ) AMPS
S E N S I T I V I T Y OF N - B U T A N E AT M A S S
Figure 6.
I
43
Sensitivity of Z41 in Mass Spectra of Mono-olefins
fairly good agreement. The rather large discrepancy in the aromatic values is probably a sampling error and not due to the method of calculation, because reliable results are generally obtained for this compound type. Analysis of several narrow boiling paraffin-aromatic mixtures is shown in Table X along with the “known” composition, which actually is that based on an accurate determination of all the compounds in the mixture. Such analyses, in general, agree within *4% in the case of paraffins and * 0 . 5 % for aromatics, although paraffins appear systematically low in the compoundtype method. These samples, however, were calculated some time before the present method of analysis was devised and such systematic errors are believed to be no longer present.
SENSlTlVlTY
Figure 7.
Of
N-BUTANL
AT MASS 4 3
Sensitivity of 269 in Mass Spectra of Mono-olefins
A serious source of error results from the lack of calibration compounds of the olefinic type, particularly the cyclomono-olefins, for which sensitivity data are the least reliable of all compounds. Determination of these compounds is undoubtedly the most inaccurate part of the analysis on a relative basis, although the error is reduced somewhat by use of the check calculation provided.
ANALYTICAL CHEMISTRY
436 Table XI.
Deviation of Sensitivity for CI-CS Paraffins
Compound Isobutane n-Butane Isopentane n-Pentane n-Hexane 2-Methylpentane 3-Methylpentane 2,P-Dimethylbutane 2,3-Dimethylbutane n-Heptane 2-Alethylhexane 3-Methylhexane 3-Ethylpentane 2,Z-Dimethylpentane 2,3-Dimethylpentane 2 4-Dimethylpentane 3:3-Dimethylpentane 2,2,3-Trimethylbutane n-Octane 2-hlethylheptane 3-Met hylheptane 4-hlethylheptane 2,3-Dimethylhexane 2,4-Dimethylhexane 2,5-Dimethylhexane 3.3-Dimethvlhexane ' 3;4-I>itnethilhexane 2.2,3-l'riniethylpentane 2.2.4-l'riniethylpentane
2.3.3-Trirtiethslpentane 2.3..l-Triil.erhvlFentane Cyclopentane Methylcyclopentane Cyclohexane hlethylcyclohexane E t h lcyclopentane 1,l-himethylcyclopentane cis-1,2-Dimethylcyclopentane trans-1 2-Dimethylcyclopentane czs-1 3-'Dimethylcyclopentane trand-1,3-Dirnethylcyclopentane 1,l-Dimethylcyclohexane cis-1 2-Dimethylcyclohexane trans-1.2-Dimethylcyclohexane cis-1 3-Dimethylcyclohexane trani-1 3-Dimethylcyclohexane cis-l,4-'Dimethyicyclohexane trans-l,4-Dimethylcyclohexane 1-hlethyl- 1-ethylcyclopentane
Maximum % Deviation of 4 v . Sensitivity Curve from Pure Compound 243 271
-5 6 6 - 15 14
- 25
-1 15 -4 12
187
- 53 305 - 69 - 22 -6
- 13 - 14
- 22 26 - 11 - 22
-31 -3 42 110 - 60
-5
- 19
6
-2
5
-1 -2 9 - 14 3 - 18 24 15 -2 -5 - 10 241
-io
20
63 -3
- 30 - 13 - 16 44
- 49
40 500 300 - 34 - 34
569
- 38 - 14 - 47
14 20 20
55
2 1
l5
} 15 16 -31
40
83 66 41
1-24
CALCULATIONS
s from 1. A gasoline sample of 57.3-micron pressure m ~ a scanned mass 32 to 186 a t a magnet current of 0.70 ampere. Peaka in the mass spectra necessary for the calculation were:
- 29
m/e
j33
A.?
154
-9 -6
11 - 18
I
I
16
(see calculations 3b and 3c), as these vary somewhat with the ratio of cycloparaffin to mono-olefin.
- 34
132
i
43
Figure 8. Sensitivity of 277 in Mass Spectra of Aromatics with Saturated Side Chains
}-24
1-16 Isopropylcyclopentane n-Prop ylcyclopentane 1 1 2-Trimethylcyclopentane 1:l:3-Trimethylcyclopentane cts,c~~,cis-1,2,3-Trimethylcyclopentane cis,czs,trans-1,2,3-Trimethylcyelopentane cis,trans,cis-1,2,3-Triinethylcyclopentane cis,cis,~~ans-1,2.4-Trimet hylcyclopentane cis,tran8,n's-l,2,4-Trimethylcyclopentane
SENSITIVITY OF N-BUTANE AT MASS
- 21
11 - 13 20 - 23
PO
MAONETIOCURREYT i0.70 AMPS
I
I
166
'
+
41 43
m/e+
Peak Height
91 92
102 1356 1491 111 104 577 572 136 171 79 19.9 172 560 403
96 97
607 179 3.8 14.0 215 65.5 602 193 81.4 182 0.6 56.4
176 _ ..
95 ..
:1 :
106 119 120 133 134
i47 148
'0
2. Calculation of 2 values (figures in parenthces reprment m / e + values). (41) Z41 = 1920 = 4413
The presence of such compounds in catalytically cracked gasoline has been definitely established, however, by analyses such as reported in Table IX. Resolution of mono-olefins and cycloparafis is based on bromine number or nitrosation and is consequently subject to the limitations of these methods. rlccording to a recent article by Dinneen et al. ( 4 ) nitrosation is more reliable than bromination, as olefins determined by the latter method may be systematically high. Because mono-olefins are calculated as the difference between olefins determined chemically and the coda compounds of the mass spectrometer analysis, validity of the chemical determination is of prime importance. Of lesser concern than the mono-olefin value itself is the effect that this determination has on the selection of pattern coefficients to be used in calculations
Peak Height 1920 2349
(6:)(83) + (551 1306 + 571 + 560
Similarly, 243 = 4815 253 = 278
271 = 1041 277 = 2287
267 = 425 269 = 1352
3a. A molecular weight determination based on the microburet technique ( 13, f 7 ) indicated that eight carbon atoms per molecule should be used in calculations. b. A bromine number indicated approximately 25'% olefin material. The selection of pattern coefficients for the cycloparaffin-mono-oleh group was based on a 50-50 distribution of these two t pes of compounds. (Had the bromine number indicated 0% o&ms, for instance, coefficients corresponding to cycloparaffins only would have been used.) c. Using the coefficients shown in Table VI1 and the mas8 spectra of the mixture, four simultaneous equations were set a8 follov,-s: 0.266 P 1.00 O&C.P. 0.75 Coda 0.012 A = 4413 1.00 P 0.26 O&C.P. 0.13 Coda 0.004 A = 4815
++
+ +
+ +
V O L U M E 23, NO. 3, M A R C H 1 9 5 1 0.0047 P 0.0015 P
437
+ 0.105 O&C.P. + 1.00 Coda + 0.0004 A = 425 + 0.014 O&C.P. + 0.08 Coda + 1.00 A = 2287
On a routine basis precalculated inverse solutions are used t o solve such equations. These inverses reduce the analysis time and also enable a calculator to employ various combinations of coefficients for a single sample. This latter procedure is followed whenever a partial calculation indicates that a cycloparaffinmono-olefin distribution other than that being used is applicable. Choice of pattern coefficients is limited to five cycloparaffinmono-olrfin ratios-namely, 0, 0.33, 1.0, 3.0, and m. Partial Solution Sensitivity. Pressure, P hlilihtttic paraffins = 3942 190 (Figure 2) 20.8 Mono-olefins and/or cycloparaffins = 3293 121 (Figures 4,6) 27 2 Coda = 59 1.50 1; Aromatics = 2230 176C (Figure 8) “ Based on n-butane sensitivity of 74.5 a t mass 43. b Sensitivity of 267 coda value is estimated b y equation: sensitivity = 0.85 X sensitivity 277 of aromatics. This equation represents a n a p r m x i rnation of sensitivities observed for compounds in Table VI. I t has n o known theoretical significance and was selected for convenience only. C T h e sensitivity of 277 for the aromatics is determined graphically hy using a value for t h e average number of carbon atoms which is 0.4 kinit bigher t h a n the average determined. I n this case, therefore, the sen-itivity of 176 was t h a t obtained for 8.0 0.4 or 8.4 carbon atoms per molecule. Basis for this procedure lies in the empirical observation t h a t the mean molecular weights of aromatics in a nurnher of gasoline blends were consi3tently higher t h a n the rest of the sample. [n many cases, however, this correction may not be justified and should be checked when applied t.o a mimhrr of samples from t h e same source.
b. The coda type compounds are next checked by calculating a residual 253 : 253
3
278, A(253) =
The negative residual indicates the absence of coda type compounds. Had a positive answer been obtained, the residual peak would have been converted to a partial pressure, using a sensitivity value 37.8, which is estimated by the equation, Sensitivity of 253
=
4. Check Calculations. a. The paraffins and mono-olefins are further checked by means of two simultaneous equations based on 269 and 271. To do this, contributions of ocher types must be removed-for example: 269
1352, A(269) = 1352
-
59 X 0.25 - 2230 X 0.00
271
= 1337 1041, A ( 2 7 1 ) = 1041 = 1039
-
59 X 0.002 - 2230 X 0.0008
Equatiorw. 0.085 P 1.00 0 k C . P . 1.00 P 0.095 0 k C . P .
+ +
= =
1337 1039
Solution I’araffim Olefins
- oycloparaffins
= =
921 1259
Sensitivity 1 2 . 5 (Figure 3) 56 8 (Figure 5 )
Partial Pressure. P
17.6 22.2
0.4 (sensitivity of n-butane a t mass 43)
+8
5 . Sormally, samples are reported in terms of volume per cent. T h r final calculation would therefore be outlined:
;
+
278 - 3942 X 0.016 - 3293 X 0.063 2230 X 0.017 -30
Partial presuure Method 1 Method 2 Mean Mole to volume factor (Figure 9) Volume Volume R
MiCycloparafphatio fins and/or ParafMonofins olefins Coda
.4romatics
20.8 17.6 19.2
27.2 22.2 24.7
0.4 0.0 0.2
12.7 l2:7
1.63 31.3 37.2
1.47 36.3 43.0
1.43 0.3 0.4
1.28 16.32 = 8 4 . 2 1 9 . 4 2 = 100.0
CONCLUSlON
Gitsoline distillates and petroleum solvents may be analyzed according to compound type on a Consolidated hlodel 21-101 mass spectromrter equipped with a modified inlet system. Constituent compounds, such as aliphatic paraffins; cycloparaffins and /or mono-olefiris, cyclo-olefins, diolefins, and/or acetylenes; and aromatics are determined within +4y0 Monoolefins are determined by bromine number or nitrosation. Three man-hours are required for a complete analysis and i t is believed the data presented here can be used directly by other users of mass spertrometers ACKNOWLEDGMENT
The author wishes to thank W. S. Young for helpful advice given during the progress of this Fork, and Frances Galbraith, Vilma illanganaro, Betty Hollis, and G. L. Martin for compiling the extensive mass spectral data. The help of Joseph Colucci, P. J. Contino, and Joseph Spontak in carrying out the experimental program is also gratefully acknowledged. LITERATURE CITED
(1) Bond, G. R., Jr., IND.ENG.CHEM.,ANAL.ED., 18, 692 (1948). (2) Brewer, A. K., and Dibeler, V. H., J. Research Natl. Bur. Standards, 35, 125 (1945). (3) Brown, R. A., Taylor, R. C., Melpolder, F. W., and Young, W. S., ANAL.CHEM..20, 5 (1948). (4) Dinneen, 0.U., Smith, J. R., and Ball, J. S., Petroleum Refiner, 29. No. 5. 129 (1950). ( 5 ) Faragher, W. F., RIorrell, J. C., and Levine, I. M., IND.ENCI. CHEM., ANAL.E D . , 2, 18 (1930). (6) Gifford, A. P.. Rock, 8. M., and Comaford, D. J., ANAL.CHEM., 21, 1026 (1949). (7) Johnsen, S. E J., Ibid., 19, 305 (1947). (8) Kurtz, S. S., Jr., and Headington, C. E., IND.ENQ.CHEM., ANAL.ED.,9, 21 (1937). (9) Kurtz, S. S., ,Jr., Mills, I. W.,Martin, C. C., H a r v e y , W. T., and Lipkin, M. R., ANAL.CHEM.,19, 175 (1947). (10) Langer, Alois. and Fox, R. E., Ibid., 21, 1032 (1949). (11) Mair, 0. .J.. J . Research SatE. Bur. Standurds, 34, 436 (1945). (12) Taylor, R. C., Brown, R. A., Young, W. S., and Headington, C. E., . ~ N A L . CHEM.,20, 396 (1948). (13) Taylor, R. C., and Young, W. S., IXD.ENG.CHEM.,ANAL.ED., 17, 811 (1945). (14) Thomas, R. W.,a n d beyfried, W. D., ANAL.CHEM.,21, 1022 (1949) (15) Thomas, C . L.. Blooh. H. S., and Hoekstra, IND. ENCT. CHEM., ANAL.ED., 10, 153 (1938). (16) Washburn, H. W., W h y , H. F., Rock, S. M., and B e ~ v y C, . E., Ibid., 17, 74 (1945). (17) Young, W.8.. and Taylor, R. C., ANAL.CHEM.,19, 133 (1947). \ - - - - ,
Figure 9.
Mol. to Volume Factors for G to Clz Hydrocarbons
RECEIYEDM a y 12, 1950. Presented before the Division of Analytical Chemistry a t the 117th Meeting of t h e AMERICAN CHBMICAL SOCIETY,Hoiiston, Tex.
