not likely to lead to exact values for p j and q1 since the isotopic composition of the constituent elements of the compound being studied will never be known exactly. If isotope abundancies were known exactly, such calculations would yield exact results. Thus, in theory, a calibration graph for a particular determination could be drawn without reference to any experimental observation using a standard material. In practice, natural variation in the isotopic composition of elements will be sufficient to make such a procedure unsafe and, in addition, an accurate value for the enrichment achieved in the labeled material is unlikely to be available. On the other hand, the values obtained will be sufficiently close approximations to the truth to act as a guide to the likely success or failure of a potential assay procedure. Such calculations may also be of use in assessing the enrichment achieved vs. the enrichment expected for labeled internal standards. The second part of the theory, summarized in Equation 17 is of particular use in calculating the results of assay procedures. In theory, it will always be better to fit the data corresponding to an experimentally determined calibration graph to Equation 17 since this equation should exactly describe the data. In practice, it may be that as the special cases outlined in Equations 18 and 19 are approached, fitting the points to the equation for a straight line will not give significant error. Whether or not this is so will depend on the circumstances of each individual assay procedure. In any event, an assay procedure is always improved by a
proper understanding of its underlying principles; accordingly, it is to be hoped that the relationships outlined above will be of use in analytical practice.
LITERATURE CITED (1) A. M. Lawson and G. H. Draffan, Prog. Med. Chem., 12, 1 (1975). (2) H. F. Holland, R. E. Teets, M. A. Bieber, and C. C. Sweeley, "A Proposed Standardisation of the Method used in the Calculation and Presentation of Data from isotope Dilution Experiments," 21st Ann. Conf. Mass Spectrom., San Francisco, Calif., 1973. Am. SOC.Mass Spectrom., N.C.-4, pp 55-9 (1973). (3) J. R. Chapman and E. Bailey, J. Chromafogr.,89, 215 (1974). (4) M. G. Horning, W. G. Stillwell, J. Nowlin, K. Lertratanangkoon, D. Carrol, I. Dzidic, R. N. Stillwell, and E. C. Horning, J. Chromafogr., 91, 413 (1974). (5) W. F.Holmes, W. H. Holland, B. L. Shore, D. M. Bier, and W. R. Sherman, Anal. Chem., 45, 2063 (1973). (6) J. E. Holland, C. C. Sweeley, R. E. Thrush, R. E. Teets, and M. A. Bieber, Anal. Chem., 45, 308 (1973). (7) J. F. Pickup, Ann.,Clin.Blochem., 13, 306 (1976). (8) H. Hintenberger, A Survey of the Use of Stable Isotopes in Dilution Analyses", in "Electromagnetically Enriched Isotopes and Mass Spectrometry", M. L. Smith, Ed., Butterworth, London 1956, p 177. (9) R. K. Webster, "Isotope Dilution Analysis" in "Advances in Mass Spectrometry", I. D. Waldron, Ed., Pergamon, London, 1959, p 1. (IO) P. D. Klein, J. R. Haumann, and W. J. Eisler, Anal. Chem., 44, 490 (1972). (11) B. Samuelson, M.Hamberg, and C. C. Sweeley, Anal. Biochem., 38, 301 (1970). (12) L. Bertilsson, A. J. Atkinson, J. R. Althous, A. Harfast, J-E. Lindgren, and B. Holmstedt, Anal. Cbem., 44, 143 (1972).
RECEIVEDfor review February 18, 1976. Accepted June 29, 1976.
Characterization of Sulfur-Containing Polycyclic Aromatic Compounds in Carbon Blacks M. L. Lee and Ronald A. Hites" Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Mass. 02 139
Computerlzed gas chromatographicmass spectrometry and high resolution mass spectrometry have been used to identify sulfur-containing polycyclics and polycyclic aromatic hydrocarbons in carbon blacks obtained from sulfur-containing petroleum feedstocks. Twenty-eight compounds have been identlfied, seven of whlch are sulfur-containing polycyclics.
Carbon black is a material of considerable commercial importance: More than 1.5 billion pounds per year of domestic carbon black are used in the manufacture of tires alone (1). It is also a material of potentially great environmental concern because of (a) wide environmental distribution of carbon black, primarily in automobile tire dust, and (b) the potent carcinogenicity of a number of compounds adsorbed on carbon black such a,s certain polycyclic aromatic hydrocarbons (PAH). These considerations have led to several studies of the organic compounds associated with carbon black. For example, two recent studies (2, 3 ) reported the identification of cyclopenta[cd]pyrene as a major constituent of carbon black extracts; in addition, 11other PAH ( 2 )and several oxygenated polycyclics ( 3 )were also reported. This paper reports on the analysis of organic extracts of several carbon blacks which were manufactured under varying conditions. Of particular interest is the first reported identification of sulfur-containing polycyclics in carbon black. In addition, the detection of high-boiling PAH has been extended to include compounds of molecular weights up to 376 (C30H16). Capillary column gas chromatography combined with mass 1890
spectrometry (GC/MS) has allowed the positive identification of 21 compounds and the tentative identification of 10 others (see Figure 1).High-resolution mass spectrometry (HRMS) of these same samples has verified the elemental composition of individual compounds, especially for the sulfur polycyclics.
EXPERIMENTAL Samples of four different furnace blacks (see Table I) were obtained from a commercial source (Cabot Corporation, Boston, Mass). The aromatic feedstocks used in the production of three of these furnace blacks were derived from refinery and naphtha-based ethylene type tars. They were over 90% aromatic hydrocarbons, and had a considerable amount of organic sulfur (1.2-3.1%). Appropriate amounts (see Table I) of each furnace black were extracted with methylene chloride for 18 h in a Soxhlet apparatus. Soxhlet thimbles were extracted with Nanograde methylene chloride (Mallinckrodt) for several hours prior to each sample extraction to remove any organic contaminants in the thimble or apparatus. The methylene chloride extracts were then evaporated to minimal volumes (1-10 ml) by rotary evaporation under Figure 1. Compounds identified in carbon blacks by GC/MS and HRMS a Structure is presumed correct but has not been verified by comparison with authentic compounds. Exact position of benzo group is not known. The increase in molecular weight of PAH species also increases the number of possible isomers: the lack of authentic compounds in this molecular weight range prevents the elucidation of the exact structures for these particular GC peaks. The structures given are examples only; many other isomers are possible. Detected only by high resolution mass spectrometry. The structures given are examples only: many other isomers are possible
ANALYTICAL CHEMISTRY, VOL. 48, NO. 13, NOVEMBER 1976
@ naphthalene
18
IO
a
'*
q
& II
acenapht hy lene
benrorq]dibenzothiophene
fJQ 3
26'
benzordef] naphthobenzot hiophene
pyrene
2
&
19 benzo [ ~ I p y r e n e
d iben zat h io p h e n e
28' 12 benzo[ghi] - fluorant hene
4 phenanthrene
benzo [a] - pyrene 2gd
a 5 anthracene
13 c y c l open t o [g] pyrene
21 p e r y lene
S
30d 6 4~ -cyclopenta phenanthrene
[&I-
14 b en z Q.] anthracene
22
8
I n d e n a [I , 2 , 3 - d 1 pyrene
3Id
0
15 chrysene f luoranthene
23
a
benzo [ghi]pery Iene
0
benz u a c e n a phthylenea
benzall] f luoranthene and b e n z o k ] fluoranthene
24 anthant hrene
benzo[def] dibenzathio phenea 17 b benzof luoran thene
25 coronene
ANALYTICAL CHEMISTRY, VOL. 48, NO. 13, NOVEMBER 1976
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'-1 26
A ' r 2-7 l
n~
TIME(MIN)
I
I
I
I
0
10
20
30
740
Figure 2. Packed-column gas chromatograms of the extract of ( A ) furnace black 1 and (B)furnace black 3 (see Table I).GC conditions: See text. Key: See Figure 1
Table I. Carbon Black Characteristics
No. Feedstock 1 Ethylene tar 2 Refinerytar 3 Naturalgas 4 Ethyleneand refinery tars
Weight of carbon Yield Furnace Particle black of temp, size, extracted, PAH, K nm g % 1400-1600 260 8 0.2 75 2 0.1 1400-1600 1400-1600 75 2 0.1 1800-2000 30 34 0.01
vacuum prior to gas chromatographicanalysis. The total yield of PAH from the four carbon blacks is given in Table I. Gas chromatographic mass spectrometry of each sample was performed on a Hewlett-Packard 5982A GC/MS system interfaced to a HP 5933A data system. A 19 m X 0.26 mm i.d. glass capillary column coated with SE-52 methylphenylsilicone stationary phase was used to separate mixtures prior to mass spectral analysis. The oven temperature was programmed from 70 to 250 "C at 2 "C/min during each 1892
chromatographic run. High-temperature gas chromatograms were run on a HP 5720A gas chromatograph with a 180 cm X 0.32 cm 0.d. stainless steel column packed with 3% Dexsil 300 on 80/100 mesh Chromosorb W which was programmed from 70 to 370 "C at 12 "C/ min with a carrier gas flow rate of 25 ml/min. High resolution mass spectral information was obtained on each sample by introducing an aliquot of the methylene chloride extract into a high-resolution mass spectrometer through a direct introduction probe system and slowly vaporizing the sample at a continually increasing temperature while several exposures on a photographic plate were made. After development, the plate was read on a computerized comparator, and the exact masses were converted to elemental compositions. The HRMS system consists of a DuPont Instruments 21-HOB mass spectrometer and a D.W. Mann comparator interfaced to an IBM 1802 computer. This system and its operation have been previously described elsewhere ( 4 ) .Both mass spectrometers were operated at 70-eV ionizing energy.
RESULTS AND DISCUSSION Figure 2 compares packed-column gas chromatograms of extracts from furnace blacks 1 and 3 (see Table I). Peak numbers refer t o compounds listed in Figure 1 which were identified by gas chromatographic mass spectrometry and retention data. In all cases where an exact identity is reported,
ANALYTICAL CHEMISTRY, VOL. 48, NO. 13, NOVEMBER 1976
TEMP InCl
70
90
I
110
130
150
170
the mass spectrum and GC retention time were identical with those of authentic materials. The gas chromatograms of extracts from carbon blacks 2 and 4 are very similar to that of carbon black 3 (Figure 2B) and are, therefore, not shown. These GCIMS data, taken together with the PAH yields given in Table I, indicate that the amounts and structures of PAH associated with carbon blacks are quite dependent on the conditions of carbon black formation. Wallcave et al. (2) found that of eight carbon blacks examined, cyclopenta[cd]pyrene was not detected in three of them and varied considerably in concentration in the others. Of the four furnace blacks analyzed in this study, the organic composition of number 1 differed substantially from the other three, which were qualitatively quite similar to one another. Furnace black 1was manufactured by a different process than 2 and 3, although furnace temperatures were the same. In addition, the higher furnace temperature used in the production of number 4 seemed to reduce the total amount of PAH by a factor of ten as compared to the others, although the qualitative distribution of PAH was still very similar to 2 and 3. The main difference in the manufacture of 2 and 3 was the nature of the feedstock used. A high-resolution gas chromatogram of the extract of furnace black l is shown in Figure 3. Again, numbers refer to compounds identified and listed in Figure 1.In addition to the identification of a number of previously unresolved isomers and trace compounds, four sulfur-containing polycyclic aromatic compounds were detected. However, because of the unavailability of standard compounds, exact identification of only dibenzothiophene and benzo[a]dibenzothiophene could be made. On the other hand, proposed structures (see Figure 1)seem to be reasonable when compared to structures of PAH identified in the same mixture. For example, although there are a number of possible structures for C I ~ H ~ the S, similarity in the structures of benzo[def]dibenzothiophene and pyrene and the closeness in chromatographic retention of both compounds give strength to the proposed assignment. Furthermore, in the pyrosynthesis of benzo[def]dibenzothiophene, a sulfur bridge could be added across the 4 and 5 positions in phenanthrene analogous to the addition of a methylene goup or an ethylene group to form 4-H-cyclopenta[def]phenanthene or pyrene, respectively. Verification of the presence of these four sulfur polycyclics and detection of an additional three (Figure 1; numbers 29-31)
190
210
230
I
250
were accomplished by high-resolution mass spectrometry as previously described. Again, proposed structures were derived from related hydrocarbons present in the fraction. The absence of sulfur compounds in the carbon black produced from natural gas (see Figure 2B) as compared to their detection in all carbon blacks produced from sulfur-containing feedstocks indicates that organic sulfur persists in the combustion of sulfur-containing petroleum feedstocks and appears as stable sulfur polycyclic compounds associated with the carbon black product. The carcinogenic activity of a particular compound is very dependent on its structure. Shape, size, electronic, and steric factors all seem to be important. For example, the addition of alkyl substituent groups in different positions on the ring of certain PAH can either have an activating or deactivating influence ( 5 , 6 ) .Similarly, the substitution of a sulfur for an ethylene group in a ring may increase or decrease the carcinogenic activity of that particular compound (7, 8). These considerations, coupled with the recent identification of many sulfur-containing polycyclics in air particulate matter ( g ) , clearly indicate that information about these compounds must be included in future studies concerning the environmental hazards of carbon black.
ACKNOWLEDGMENT We thank Cabot Corporation, Boston, Mass., for supplying samples of various carbon blacks and for providing some of the information given in Table I. LITERATURE CITED (1) Chem. Eng. News, April 5, 1976,p 8. (2)L. Wallcave, D. L. Nagel, J. W. Smith, and R. D. Waniska, Environ. Sci. Techno/., 9, 143 (1975). (3) A. Gold, Anal. Chem., 47, 1469 (1975). (4)K. Biemann in "Applicationof Computer Techniques in Chemical Research", Institute of Petroleum, London, 1972, pp 5-19. (5) R. Schoental, in "Polycyclic Hydrocarbons",E. Clar, Ed., Academic Press, London, 1964,p 133. (6) D. Hoffmann, W. E. Bondinell, and E. L. Wynder. Science, 183,
215 (1974). (7)5.D. Tilak, Tetrahedron, 9,76 (1960). (8) E. Campaigne, D. R. Knapp, E. S. Neiss. and T. R. Eosin, Adv. Drug Res.,
5, l(1970). (9) M. L. Lee, M. Novotny, and K . D. Bartle, And. Chern., 48, 1566 (1976).
RECEIVEDfor review May 26,1976. Accepted July 19,1976. This work was supported by Grant R803242 from the U.S. Environmental Protection Agency.
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