(4) (5) (6) (7) (8) (9)
A. R. Troiano, Trans. Am. Soc. Met., 52, 54 (1960). R. A. Oriani and P. H. Josephic, Scr. Metall., 6, 681 (1972). D. G. Westlake, Trans. AIM€, 245, 1969 (1969). T. W. Wood and R. D. Daniels, Trans. AIM€, 233, 898 (1965). M. L. Grossbeck,Ph.D. Thesis, University of Illinois, Urbana, iil., 1975. D. K. Bakale, B. N. Colby, and C. A. Evans, Jr., Anal. Chem., 47, 1532 11975).
(10) A.E.-knner and B. P. Stimpson, Vacuum, 24, 511 (1974). (1 1) T. Schober, M. A. Pick, and H. Wenzl, fhys. Status Solidi A, 18, 175 (1973). (12) 8. J. Makenas,H. K. Birnbaum,and H. L. Fraser, to be published.
RECEIVEDfor review October 14, 1975. Accepted February 12, 1976. This work was supported by the National Science Foundation under Grants DMR 72-03026 and MPS 72~~~~~~~h under contract 05745, the Office of N00014-67-A-0305-0020, and the U.S. Energy Research and Development Administration under Contract AT( 111)-1198.
High Resolution Mass Spectrographic Method for the Analysis of Nitrogen- and Oxygen-Containing Material Derived from Petroleum A. W. Peters* and J. G. Bendoraitis Mobil Research and Development Corporation, Research Department, Paulsboro, N.J. 08066
A high resolutlon (15 000-25 000) high voltage (70 eV) mass spectrographlc method for the analysis of N,O-contalnlng fractlons of petroleum has been developed. The method permits mass and Intensity measurements on up to 2000 peaks per spectrum, and provides intensity percentagesfor arbltrary compound classes. The results are consistent wlth the Robinson and Cook method when applled to aromatic petroleum fractlons. The method Is also applied to shale oils and nltrogen-enriched petroleum fractlons.
In recent years, there has been significant progress in the mass spectroscopic analysis of petroleum fractions by both high and low resolution methods. Lumpkin ( 1 ) and Hood and O'Neal(2) have developed analyses applicable to the saturate hydrocarbon fraction and, recently, Robinson and Cook (3, 4 ) , Gallegos (5),and Takeuchi (6) have developed relatively complete analyses for most of the major sulfur types in the aromatic fraction. In view of these developments, there is limited incentive to develop additional methods for the analysis of the hydrocarbon portion of petroleum. There is, however, a considerable interest in the determination of the nitrogen- and oxygen (N,O)-containing types both in petroleum and in shale and coal derived liquids. In this area, the methods of analysis are much less well developed. High resolution methods are required, as well as a separation scheme to provide samples enriched in the N,O-containing polar components. Snyder (7) has recently developed a chromatographic method for separation of various compound types. The compound types in each fraction were identified by high resolution low voltage mass spectroscopy. Aczel et al. (8) have developed a low voltage high resolution method for the determination of polar types. The method has the advantage of being routinely applicable, and has been applied to the analysis of coal oils (9). In this paper, we report the development of a high voltage, high resolution (15 000-25 000) mass spectrographic technique specifically designed for the analysis of complex mixtures of nitrogen- and oxygen-containing compounds. The use of high ionizing voltage allows the analysis of non-aromatic as well as aromatic samples, and also provides an advantage in the analysis of samples containing a high percentage of nitrogen. Nitrogen-containing types are not easily resolvable from hydrocarbon types in the low voltage spectrum, since the mass range of the parent ions is from 250 to 500 amu. However, 968
ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
at high voltage, the major nitrogen-containing fragments occur a t a relatively lower mass (100 to 250 amu) and are clearly resolved from hydrocarbon fragments. Since high voltage operation produces many more ions and a much higher ion current than low voltage operation, photographic detection, in spite of its inconvenience, offers a reasonable alternative to electrical detection. Intensities are integrated with time, allowing one to handle relatively small samples, and also to detect weak peaks at optimum resolution. This is an important feature, since a typical petroleum sample may produce 1000 to 2000, or more, peaks under high resolution, and even a relatively intense peak of 5% of the base peak may represent only 0.01 to 0.1% of the total ion intensity. Examples of the use of the method described here include applications to raw and hydrotreated shale oils, polar petroleum fractions, and to fractions of aromatic and sulfur-containing material derived from petroleum. In the case of the aromatic hydrocarbon- and sulfur-containing samples, the results are consistent with the Robinson and Cook analysis.
EXPERIMENTAL The high resolution spectra were obtained using a duPont CEC 21-llOB high resolution mass spectrometer equipped with a bilateral source slit and both photoplate and electrical detection systems. Both Ilford Q2 photoplates, developed at 25 "C with Microdol X, and the Ionomet evaporated AgBr photoplates (Ionomet Co., P.O. Box 56, Waban, Mass. 02168) were used. Position and optical density data were obtained with a Grant-Datex comparator microphotometer (10) (Grant Instruments, Inc., Berkeley, Calif.) equipped with a 49X Kinoptic lens. The data were reduced by a modified version of Hi Res I, a program developed by Tunnicliff and Wadsworth ( I I ) , and by other original programs written in FORTRAN for an IBM 370 computer. Polar fractions were separated by column chromatography using Florisil (Floridan Co., distributed by Fisher Scientific) 100-200 mesh saturated with 6%water. At a Florisil to oil ratio of l O / l , a 1.0-gsample is dissolved in a small amount of cyclohexane and placed on the column. The nonpolar material including polynuclear aromatics,is eluted with 400 ml of n-pentane and the polar fraction is subsequently eluted with dichloromethane and, if necessary, with acetone. Fractions isolated by gradient elution chromatography were obtained as described in reference (12). The shale oil was obtained from The Shale Oil Corporation (TOSCO) and was hydroprocessed at Mobil. Samples 71A, 71B, and PG 369-378were obtained from Section M (RD IV), ASTM Committee D-2 of the American Society for Mass Spectrometry. All low resolution mass spectra were obtained from a Hitachi RMU-6 mass spectrometer.
Table I. Calculated Exact Masses for Some Typical Ions from a High Sulfur Gas Oil Sample” B. Benzothiophene Types A. Phenanthrene Types Obsd
Calcd
Formula
(mmu) Error
Obsd
Calcd
Formula
(mmu) Error
161.0391 Ci3H5 $2.3 +3.8 161.0414 163.0548 Ci3H7 161.0425 CioHgS -1.1 -0.4 163.0583 CioHiiS 175.0548 C14H7 +3.3 +3.0 175.0581 177.0734 177.0704 CidHg 175.0582 CiiHiiS -0.1 -0.4 177.0738 CiiHi3S 191.0830 191.0861 Ci5Hii -3.1 189.0719 189.0704 CisHg +1.5 -6.5 189.0738 CISHISS -1.9 191.0895 CiZH15S 205.1017 205.1017 CxHi3 0.0 203.0884 203.0861 CiGHii +2.3 -3.4 203.0895 Ci3Hi5S -1.1 205.1051 C13Hi7S 219.1180 219.1174 Ci7H15 +0.6 217.1030 217.1017 Ci7Hi3 +1.3 -2.8 217.1051 C14Hi7S -2.1 219.1208 Ci4HigS 0 Sample 71A received from Section M (RD-IV) of ASTM Subcommittee D-2 of the American Society for Mass Spectrometry. 163.0586
0
MASS AND INTENSITY MEASUREMENTS The first part (Hi Res I) of the Tunnicliff and Wadsworth program gives the position of the centroid of all peaks ( 1 1 ) . T h e relation between the mass and position of peaks on a typical photoplate is given by
Mf - M.f = C ( X 1 - X,)
= hM1.2 exp
,-
(1)
where M i , M2 and X i , Xq are the masses and positions of two peaks and P is a constant with a value of approximately 0.5. Normally high resolution spectra include peaks from a reference material such as perfluorokerosine. Given two reference peaks of known mass and position, Equation 1 may be used t o identify additional reference peaks by extrapolation to higher and lower masses until all reference peaks in the spectrum are identified. The masses of unknown sample peaks are then computed by interpolation, again using Equation 1. T h e final list of masses is an average of the values computed using all binary sets of reference masses which are reasonably close to and bracket the unknown masses. Table I gives examples of the accuracy of the mass measurements obtained with petroleum samples. Columns A and B list the masses of fragments from phenanthrene and benzothiophene types as determined for a high sulfur (6.6%) gas oil. Peaks at m/e 163,177,161,and 175 are expected to contain sulfur, consistent with the measured masses. The peaks at mle 191, 205, and 219 correspond to alkyl phenanthrene or anthracene fragments which are expected to be present in substantial quantity. The mass measurements of peaks a t nominal mle 189,203, and 217 indicate the presence of both hydrocarbon- and sulfur-containing ions, consistent with the expected occurrence of benzothiophene fragments as well as prominent hydrocarbon fragments a t these masses. These results are typical for high sulfur petroleum fractions and show that, in spite of some inaccuracy due to the presence of isotopes of sulfur and carbon, the exact mass measurements can be used to indicate the presence of sulfur-containing material. The determination of ion abundances from photoplate data has been difficult and uncertain and has led to a number of studies of the response of various photoplates to ionic bombardment (13-17). In the work reported here, the relationship between intensity and exposure for the Ilford Q2 plates is
I
,
I
I
-12(1000 - d ) 1000 - b
where Z is the intensity, M is the mass, d is the maximum darkening of the peak read from the Grant-Datex, and b is the darkening of the background read a t 0.5-mm intervals along the photoplate. A similar relationship is used for the Ionomet photoplates except that the mass dependence is eliminated.
xi I00
I
1,oou
-IuLLJ 10,000
RELATIVE INTENSITY
Figure 1. Plot of darkening (1 - T ) vs. ion abundance for selected peaks in the mass spectrum of perfluorokerosine with background corrections
Equation 2 is similar to the relationship given by Dornenberg and Hintenburger (13)and more recently by Hayes (14). Equation 2 implies that d is measured with respect to a line of maximum darkening, usually m/e 69, where PFK is used as a reference compound. It has been observed that the darkening for this and other saturated lines is similar, even for different batches of plates. Consequently, the Grant-Datex system is adjusted so that a reading of d = 900 is obtained for maximum darkening, while a clear plate is set to give a value of about b = d = 050. The correction for background or “fog”, as given in Equation 2, was found empirically to improve relative ion abundances without introducing excessive background dependence near upper and lower density values. The factor of 12 in the exponent of Equation 2 was obtained from a plot of (1000 - d ) / (1000 - b ) vs. log Z where I is the relative peak intensity. Although the intensity measurements of individual peaks are not entirely reliable, Figure 1 shows that intensity trends ar8 well represented over a dynamic range of about 100. The dynamic range may be extended by using graded exposures.
METHOD OF ANALYSIS The analysis was performed by summing the intensities of all M+and (M- 1)+peaks with mass greater than 100, where M+ corresponds to a possible molecular formula CnHZn+*R (R is heteroatomic group) and where (M - 1)+is a fragment ion corresponding to the loss of H+, CH3+, CzH5+, . . . . The result is a set of intensity percentages associated with the compound types defined by the value of x and the heteroatomic content, which in turn is determined by the mass measurements. Peaks containing sulfur are identified as having a mass 0.0018 amu or more greater than expected for a hydrocarbon, and are placed in separate sulfur-containing ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
969
Table 11. Analysis of Three Aromatic Petroleum Fractions" by High Resolution Mass Spectrographic (HRMS) Methods (Intensity % ) and by the Low Resolution Robinson and Cook (RC)bProcedure (Volume % ) PC-69-378 CnHZn+x Y
=
-6 -8 -10 -12
-14 -16 -18 -20 -22 -24
-28 -30
Compound type Mono aromatics Alkyl benzenes Naphthene benzenes Dinaphthene benzenes Di aromatics Naphthalenes Acenaphthenes, biphenyls Fluorenes Tri aromatics Phenanthrenes Naphthene phenanthrenes Tetra aromatics Pyrenes Chrysenes Penta aromatics Perylenes Dibenzanthracenes
71A
71B
RC
HRMS
RC
HRMS
RC
HRMS
38.8 12.1 13.4 13.3 26.2 6.1 9.4 10.7 14.0 8.9 5.1 8.5 5.5 3.0 2.0 1.5 0.5
32.7 8.0 12.4 12.3 36.6 12.7 12.3 11.6 17.0 9.5 7.5 8.3 5.6 2.7 0.5 0.4 0.1
36.4 9.5 9.3 17.6 30.2
31.0 6.3 9.3 15.4 34.9 13.7
46.9 19.7 13.8 13.4 24.8 7.8 8.0 9.0 10.7 6.9 3.8 6.9 4.6 2.3 1.9 1.4 0.5
34.8 9.7 12.9 12.2 30.0 10.2 9.6 10.2 14.6 7.5 7.1 10.1 6.1 4.0 2.7 2.0 0.7
8.1
11.5 10.6 10.1 5.6 4.5 6.8 4.4 2.4 0.4 0.2 0.2
12.1
9.1 10.8 6.2 4.6 2.0 1.0 1.0 0.0
... ...
CnHZn+xS x = Thiophenic 3.5 1.2 9.7 8.9 2.5 1.6 6.3 5.5 0.8 1.1 1.9 0.3 -10 Benzothiophenes 2.6 3.3 1.4 0.2 1.4 0.8 -16 Dibenzothiophenes 0.8 0.1 0.3 0.3 -22 Naphthobenzothiophenes 0.2 0.1 7.0 1.8 6.3 ... 6.2 3.7 Unidentified 4.3 1.8 4.7 ... 4.0 3.3 Class IV (X = -26) 2.7 ... 1.6 ... 2.2 0.4 Other Other sulfur- and oxygen... 1.8 12.4 2.5 containing material % S (Mass spec., est.) 2.0 0.3 % S (Elemental analysis) 6.6 1.0 Samples obtained from Section M (RD-IV) of ASTM Committee D-2 of the American Society for Mass Spectrometry. Ref. 3. classes. For example, of the peaks shown in Table I, those a t m/e 161, 175, and 203 would be considered as benzothiophene peaks, those a t m/e 163 and 177 would be placed in another sulfur-containing class, and the peaks a t m / e 189, 191, 205, 217, and 219 would be classed as hydrocarbons. The use of intensity summations employed here is similar to procedures previously reported. Hastings et al. (18) used summations of the most intense (M - 1)+fragment peaks for each type of interest, where M+ represents the series of molecular ions. Orkin et al. (19) selected summations of both (M - l ) +and M+ peaks for each class and assumed equal sensitivities. Robinson and Cook ( 3 ) extended the method to include sulfur-containing and polynuclear aromatic types and also included sensitivity corrections. In this work, we follow a procedure similar to that of Orkin et al., where neither sensitivities nor matrices including interference corrections are used. The use of high resolution minimizes interferences between compound types. Sensitivity corrections could be applied if more were' known about the compound types present and if reference compounds were available. However, this is not the case. The results presented in the following sections show that accurate sensitivities are not necessary to obtain a meaningful analysis. Since sensitivity corrections are not made, all of the results are reported in intensity percent.
APPLICATION TO AROMATIC PETROLEUM FRACTIONS Although a high resolution method should be most useful for the analysis of heteroatomic concentrates, it is also desirable that the method be applicable in other areas as well, as, for example, in the analysis of typical aromatic hydrocarbon fractions. In this area, the method should be comparable to 970
ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
other methods, such as the recently developed, widely used Robinson and Cook procedure. The results of the high resolution photoplate method described here and of the Robinson Cook method are listed in Table I1 for a series of cooperative samples submitted in the past few years to interested laboratories by a subcommittee of the American Society for Mass Spectroscopy. The high resolution photoplate analyses represent in each case an average of the results for three different exposures with a reproducibility of about f10% or better. The high and low resolution results are similar, especially for the polynuclear aromatic and thiophenic types. Variations in the amounts of mono- and dinuclear aromatics are expected since sensitivity corrections are not included in the high resolution method. Table I11 shows an additional comparison between the high resolution mass spectrographic and Robinson and Cook methods for three gradient elution chromatographic (12) fractions of a deasphalted Kuwait residuum. The results are again similar, especially for polynuclear aromatic and thiophenic types. The agreement between the Robinson and Cook low resolution and the high resolution mass spectrographic methods is encouraging considering the inherent differences in the two methods. The consistent agreement between the percentages calculated by the two methods shows that the intensity sums obtained from the photoplate do meaningfully reflect the composition of the petroleum fractions, and that errors in the calculation of individual intensities tend to be minimized by the use of summations over many peaks. The data can also be used to provide independent support for the effectiveness of the Robinson and Cook method in eliminating interferences between overlapping compound types. This is especially evident in the analysis for the major thiophenic types shown in Table 111. The high resolution
Table 111. Comparisons between Lowa and High Resolutionb Analyses of a Kuwait Residual Fraction Separated by Gradient Elution ChromatographyC MNA CnH~n+x Compound type x = Monoaromatics -6 Alkyl benzenes -8 Naphthene benzenes -10 Dinaphthene benzenes Di aromatics -12 Naphthalenes -14 Acenaphthenes, biphenyls - 16 Fluorenes Tri aromatics -18 Phenanthrenes -20 Naphthene phenanthrenes Tetra aromatics -22 Pyrenes -24 Chrysenes Penta aromatics -28 Perylenes -30 Dibenzanthracenes
+ DNA
RC 60.5 24.2 18.8
17.5 12.7 3.4 4.9 4.4 4.3 2.4 1.9 1.1 0.4 0.7 1.2 0.9 0.3
PNA
HRMS 39.1 11.0 13.2 14.9 36.6 15.6 13.0 8.0 11.5 6.8 4.7 4.2 2.8
1.4 0.2 01.2
...
Soft resin
RC 27.5 6.7 9.9 10.9 25.7 4.6 10.5 10.6 10.5 5.0 5.5 4.5 3.7 0.8 1.0 0.6 0.4
HRMS 16.3 5.2 4.6 6.5 28.3 11.5 9.6 7.2 12.6 6.5 6.1 8.2 5.8 2.4 0.5 0.3 0.2
RC 13.9 2.7 3.2 8.0 23.8 1.6 9.4 12.8 13.5 5.4 8.1 6.3 4.3 2.0 2.9 2.1 0.8
HRMS 6.4 1.7
20.0 16.3 2.7
17.4 15.4 1.9
1.0
0.1
10.8 3.7 7.1
0.7 0.7
18.9 5.1 10.5 3.3 20.8 7.7 n.1
16.0 2.1 9.8 4.1 5.7 5.3 0.4 .19
1.6
3.1 15.7 4.5 3.9 7.3 16.1 7.6 8.5 12.6 7.2 5.4 3.4 1.7 1.7
Cn H 2 n + x S x =
-10 - 16 -22
.o
Thiophenic Benzothiophenes Dibenzothiophenes Naphthobenzothiophenes Unidentified Class IV (X = -26) Other Other S compounds
5.2 3.3 1.6 0.3 15.0 4.9 10.1
...
2.8 2.1
0.7
... 0.5 0.5
... 5
.o.
.
.10
...
.8.
... ... ... 0.7 ... 0.2 Other 0 compounds ... ... ... Other S2 compounds ... * . . 4.8 % S (Mass spec., est.) 0.4 0.7 1.8 2.7 1.5 3.6 % S (Elemental analysis) 1.7 4.5 6.6 a Robinson and Cook method of Ref. 3 in vol. %. Method reported here in intensity %. The method and fraction designations (MNA = mono nuclear aromatics, DNA = dinuclear aromatics, PNA = poly nuclear aromatics) are given in Ref. 13. method, for which interferences are minimal, shows a high concentration of benzothiophenes in the PNA fraction and a high concentration of dibenzothiophenes in the Soft Resin fraction. The Robinson and Cook method shows an identical result. This gives strong support for the reality of the types reported by the Robinson and Cook method. APPLICATIONS T O T H E ANALYSIS OF POLAR FRACTIONS Considering the adequacy of the Robinson and Cook method, there is limited incentive to pursue the routine analysis of low sulfur aromatic petroleum samples by the much more expensive high resolution technique outlined here. A more promising application for high resolution methods is in the analysis of samples high in nitrogen and oxygen compounds. A high resolution analysis of liquids from coal expected to contain large amounts of oxygen, has been reported previously (9).Shale oils, which contain large amounts pf nitrogen, are especially difficult to analyze since it is necessary to resolve the nitrogen-containing types from the hydrocarbon types (20). A resolution of nearly 20 000 is required a t mass 200 and, a t this resolution, it is necessary to measure the mass and intensity of about 1000 peaks. Table IV gives the high resolution mass spectrographic analysis of 320 to 430 "C distillate fractions of a hydrotreated and an untreated Tosco shale oil. The total percentage of nitrogen agrees reasonably well with determinations made by the Kjeldahl method. It can be observed from these results that the removal of nitrogen is nonselective, in agreernent with the results of other studies (21). The resolution achieved is illustrated in Figure 2 which
211.1349
211.1492
C15H17N - 1.2
'16 H19 f 0.5
207 95 Flgure 2. Photograph of a doublet at m/e 21 1 in a shale oil, including
the exact mass, formula,relative intensity, and mass measurement error in miltimass units for each peak shows a photograph of the oscilloscope display from the Grant comparator of a hydrocarbon and N-containing doublet a t nominal m/e 211. This represents a resolution of 17 000 on the photoplate or 26 000 a t the collector, assuming the resolution to be proportional to the radius of the magnetic sector. [Equation 1,reference (IO)is used to determine the effective magnetic sector radius a t a given position on the photoplate.] Although liquids derived from oil shale and coal are of increasing importance to the petroleum industry, the polar N,O-containing portion of petroleum is also of particular interest since the composition of this fraction may have a strong influence on catalyst activity, and generally on the quality of petroleum products. Since typical petroleum products are low ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
971
Table IV. High Resolution Analysis (Intensity % ) of the Aromatic Portion of a Hydrotreated and a n Untreated Tosco Shale Oil Boiling in the Range 320 to 430 "C Tosco Shale Oil
Table V. Intensity Percentages by Compound Type in a Polar Fraction (approximately 1% by Weight) of a Lybian Crude Distillate (350-430 "C) by High Resolution Mass Spectrographic Methods Formula
x -
-6 -8
-10 -12 -14
-16 -18 -20 -22
Untreated
Hydrotreated
Mono aromatics Alkyl benzenes Naphthene benzenes Dinaphthene benzenes Di aromatics Naphthalenes Acenaphthenes, biphenyls F 1u or en es Poly aromatics Phenanthrenes Naphthenephenanthrenes Pyrenes
36.9 10.4 9.6 16.9
61.8 18.3 20.4 23.1
27.3 9.4 10.4
24.1 12.4 5.4
7.5 3.3 2.0 1.3
6.3 3.4 2.2 0.9
...
0.3
N-Containing aromatics Pyridines Naphthenopyridines Indoles Quinolines Naphtheno quinolines Carbazoles Other N, 0, S types % N (from the analysis) % N (elemental analysis) Est. mol. w t
26.7
10.2
9.4 4.4
2.4 2.3
6.3 2.8
3.5 1.4 0.2
CnHznCnH~n+x
-6 -8 -10 -12
-14 -16
2.1
8.3 1.7
0.4 0.4 0.6
2.2
0.9
1.7
250
0.5 4.2 1.7 2.4 5.4 4.7 3.3
2 0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 -22 -24 -26 -28 -30 -32
250
C11H140t 1742
C10H1002t 89
C13H6t 498
10.7
t0.7
'0.5
-0.7
-2.4
Peak A
Peak B
Peak C
'2IH27 128
'dF6+ 3129
+
il.2
Photograph of the oscilloscope display of a multiplet at m/e 162, including the exact mass, formula, relative intensity, and mass measurement error in millirnass units for each peak
972
ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE
3.4
Peak A
Figure 3.
1976
0.3 0.9 3.9 2.5 1.4 4.7 1.9 0.6 0.9 0.1
17.2
0.4 2.0 1.5 0.6 0.6 0.3 0.1 0.4
5.9
'
nitrogen concentration was reduced to 34 ppm in the nonpolar fraction and increased to 1.3% in the polar fraction, which represented 1.1wt % of the total oil. The high resolution data were obtained from two exposures including data for 1293 and 1758 measured peaks covering a mass range of 40 to 400. Figure 3 is a photograph of the set of peaks a t nominal mass 162 obtained from the oscilloscope display of the Grant-Datex Instrument. Although somewhat overexposed, the peaks are separated and identified as shown in the figure. The resolution required to separate peaks A and B is 1 2 500 or 27 000 a t the collector, while the resolution needed to separate B from C is 8000 or 17 000 a t the collector. Figure 4 is a similar photograph of a quartet a t mass 279, showing the intensity, mle, and empirical formula calculated for each peak. The resolution
270.2147 CllHi6Ni 827
CnHzn+x " 0
1.1
0.2 0.1 0.3 0.2
6.1 5.8 5.3 0.1 8.1 2.1 0.2 6.3 1.3 0.1 4.8 0.9 3.7 0.3 2.0 0.4 2.2 0.1 1.9 0.1 0.5 0.2 0.2 0.1 Totals 47.2 27.4 2.3 % N (from the analysis) = 1.1wt % % N (elemental analysis) = 1.3 wt % % 0 (from the analysis) = 2.0 wt % % 0 (elemental analysis) = 3.8 wt % % S (elemental analysis) = 2.9 w t % Average mol wt (est.) = 300
in nitrogen, it is necessary to concentrate the polar N,O-containing material. A variety of materials may be used to provide the required separation including alumina, clay, and Florisil. I t has been found that a deactivated Florisil (6% water) can be used to prepare a polar concentrate which typically represents 0.1 to 5% of the total oil and contains from 60 to 95% of the total nitrogen. The polar material may be analyzed by high resolution methods, and the nonpolar material may be separated into aromatic and saturate fractions and analyzed by conventional methods. As an example, Table V shows an analysis of the polar fraction of a 350 to 430 "C distillate cut from a Lybian crude containing 150 ppm nitrogen. After separation on Florisil, the
C12h1BL 523
CnH2n- CnH2n+xOp +xNH
X
CnH2n+s NH x =
+xO
279.1973
\279.1115
279.1596
C20H25N 315
'20H23' 97
C19H21N0 1149
-1.4 Peak B
2.7
-2.7
Peak C
Peak D
f
Photograph of the oscilloscope display of a quartet at m/e 279, including the exact mass, formula, relative intensity, and mass measurement error in millirnass units for each peak Figure 4.
required to separate B from C is 12 000 or 20 000 a t the collector, while 22 000 or 36 000 a t the collector is required to separate A from B or C from D. This quartet represents about 0.15% of the total ionization. Although the mass spectrum does not provide direct evidence for the structures found in these mixtures, one may attempt an interpretation of the results in Table V, based on literature results and evidence from other methods. The nitrogen types (C,HZ,+~ NH) show a relatively high concentration of material in classes x = -10, -16, and -22 corresponding to alkyl indoles, carbazoles, and benzocarbazoles, respectively, all benzologues of pyrrole. Somewhat lower concentrations of material are found in classes x = -12 and - 18 corresponding to alkyl quinolines and benzoquinolines. All of these nitrogen types are commonly observed in petroleum (7). The % N calculated from the analysis agrees well with the results of elemental analysis (Dumas method). The oxygenated compounds observed include a series with the formula C,H2,02, corresponding to saturated acids or esters. Molecular ions were observed from carbon numbers C14 to C19 and fragments were observed a t CIS and lower carbon numbers. Other oxygenated materials may include naphthenic acids and aromatic alcohols. Using the separation procedure described here, benzologues of furan do not elute in this fraction and are not present in the sample, although they may be observed in the high resolution mass spectrum of the nonpolar fraction eluted with pentane. The % 0 calculated from the analysis is significantly lower than the value obtained from elemental analysis. This is probably due to the expected low sensitivity and the relatively high abundance of the C,Hz,02 type. The types of material (C,H2n+xNHO) containing the NHO heteroatom group between X = - 4 and X = -18 include amides, evidenced by substantial absorption in the infrared a t 1670 cm-l. The material in classes X = -6, -12, and -18 may correspond to alkyl pyridones and their benzologues. There is enough nitrogen and oxygen to account for the entire sample, assuming one nitrogen or oxygen per molecule, and enough sulfur to account for an additional 30%. It is probable that there is very little hydrocarbon present, and that the observed 47% hydrocarbon intensity consists primarily of fragments from heteroatomic material. Some sulfur containing fragments in benzothiophene, dibenzothiophene, and other classes were also observed. However, because of the large amount of nitrogen and oxygen present, the mass measurements are not sufficiently accurate to obtain reliable estimates of the distribution of sulfur, since the mass difference between compounds Cn--3H2n+4+xS and C, H Z , + ~ is only 0.0034 amu. Consequently, sulfur containing types with the formula Cn-3H2,+4+ ,S are included in the hydrocarbon class C,HP,+~.
It is not possible to indicate the magnitude of the errors in the analysis since reliable independent methods of analysis are not available. Although the nitrogen content estimated from the analysis is in reasonably good agreement with the value determined by elemental analysis, the estimated oxygen content is too low and the hydrocarbon content is too high. Sensitivity corrections and corrections for hydrocarbon fragmentation could be made, but because of the variability and complexity of typical samples, we have not yet been able to incorporate these corrections into a general program applicable to most samples. Rough corrections can be made, based upon the elemental analysis of each sample, and may provide a somewhat more accurate composition. In summary, the analysis is useful in providing comparisons of composition between samples of polar petroleum fractions containing heteroatoms. For example, the method can be used to identify the relative amounts of nitrogen types in shale oils or petroleum products, and to identify sulfur and oxygen types not usually determined. When applied to aromatic petroleum fractions, the method has the advantage of being consistent with the widely used analysis developed by Robinson and Cook.
LITERATURE CITED (1)H. E. Lumpkin, Anal. Chem., 28, 1946 (1956). (2)A. Hood and M. J. O'Neal, "Advances in Mass Spectrometry", Vol. 1, J. D. Waldron, Ed., Pergamon Press Ltd., London, 1959,pp 179-192. (3)C. J. Robinson and G. C. Cook, Anal. Chem., 41, 1548 (1969). (4)C. J. Robinson and G. C. Cook, Anal. Chem., 43, 1425 (1971). (5)E. J. Gallegos, J. W. Green, L. P. Lindeman. R . L. LeTourneau, and R . M. Teeter, Anal. Chem., 39, 1833 (1967). (6)T. Takeuchi, K. Matsumoto, and N. Yamamoto, Sekiyu GakkaiShi, 12,929 (1969). 41,1084 (1969); L. R . Snyder, (7)L. R. Snyder, Anal. Chem.,41,314(1969); B. E. Buell. and H. E. Howard, Anal. Chem., 40, 1303 (1968). (8)Thomas Aczel, D. E. Allan, J. H. Harding, and E. A. Knipp, Anal. Chem., 42, 341 (1970). (9)T. Aczel, J. Q.Foster, J. H. Karchmer, Am. Chem. SOC.Div. Fuel Chem. Prepr., 13,(l),8 (1969). (10)K. Biemann, Adv. Mass Spectrosc., 4, 139 (1968):R. Venkataraghaven. F. W. McLaffertyand J. W. Amy, Anal. Chem., 39, 178 (1967). (11) D. D. Tunniciiff and P. A. Wadsworth, Anal. Chem., 40, 1826 (1968). (12) W. R. Middleton, Anal. Chem., 39, 1839 (1967). (13)E. Darnenburg and H. Hintenberger, Z.Naturforsch, A, 18,676 (1961). (14) J. M. Hayes, Anal. Chem., 41, 1966 (1969). (15)S.Kinoshita, Proc. R. SOC.London, 83A, 432 (1910). (16)K. I. Grais, Appl. Spectrosc., 23, 607 (1969). (17)D. M. Desiderio, "Mass Spectrometry: Techniques and Applications", G. W. A. Miine. Ed.. Wiiey-interscience, N.Y., 1971,pp 11-42. (18)S. H. Hastings, B. H. Johnson, and H. E. Lumpkin. Anal. Chem., 28, 1243 (1956). (19)B. A. Orkin, J. G. Bendoraitis, B. Brown, and R. H. Williams, ASTM Special Tech. Pub., No. 224. Symp. on Composition of Petroleum Oils, 59,ASTM, Philadelphia, Pa., 1958. (20)B. Sirnoneit, H. Schnoes, P.Haug, and A. C. Burlingame, Chem. Geol., 7 , 123 (1971); Nature(London), 228, 75 (1970). (21)M. 0. Rosenheimer and J. R. Kiovsky, Am. Chem. SOC.Div. Petrol. Chem. Prepr., 12,(4),147 (1967).
RECEIVEDfor review August 6,1975. Accepted February 17, 1976.
Determination of Uranium in Natural Waters by Neutron Activation Analysis Ernest S. Gladney," James W. Owens, and John W. Starner Los Alamos Scientific Laboratory, P.O. Box 1663, Los Alamos, N.M. 87545
A rapid procedure has been developed for the measurement of uranium in natural waters using thermal neutron activation and anion-exchange separation of radio-uranium from ethanol/HCI solvent mixtures. Detection limits of 0.05 ppb have
been achieved with analytical precisions of f10-30%. Results of uranium analyses by this procedure and by fluorometry are compared for natural water samples from Alaska and New Mexico. ANALYTICAL CHEMISTRY, VOL. 48, NO. 7, JUNE 1976
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