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Anal. Chem. 1982, 54, 823-824
mobilization of fluoresceinamine on glass and the UNH machine shop for help in designing and constructing the fluorescence photometer.
LITERATURE CITED (1) Peterson, J. I.; Goldstein, S. R.; Fitzgerald, R. V. Anal. Chem. 1980, 52 864-869. (2) Pierce Catalog, 1979-1980. (3) Kay, G.; Crook, E. M. Nature (London) 1967. 218, 514-515. (4) Leonhardt, H.; Gordon, L.; Llvlngston, R. J . Phys. Chem. 1971, 75, 245-249.
(5) Martin, M. M.; Llndqulst, L. J. Luminescence 1975, IO, 381-390.
Linda A. Saari W. Rudolf Seitz* Department of Chemistry University of New Hampshire Durham, New Hampshire 03824
for review November 9, lg8I* Accepted January 15, 1982.
Comments om Variations in Concentrations of Organic Compounds I ncluding Polyc hIor inat ed Dibenzo-p -dioxins and Polynuclear Aromatic Hydrocarbons in Fly Ash f rorn a Municipal Incinerator Sir: Appropriate assessment of possible environmental effects arising from trace organic constituents present in combustion unit emissions require that published findings concerning such sources contain data which are carefully defined with regard to both accuracy and reliability (I). Therefore, we feel that it is necessary and appropriate to comment on the recently reported data of Eiceman, Clement, and Karasek regarding chlorinated dibenzo-p-dioxins (CDDs) observed in fly ash froim a particular municipal incinerator (2) because the described analytical procedure suffers from a systematic error which produces unreliable and biased quantitative data for CDDs. The source of this error involves the authors' procedure for determining CDDs (other than TCDDs), in particular, the gas chromatography mass sipectrometry selected ion monitoring (GC-MS-SIM) calibration technique. As stated, a HewlettPackard 5992 quadrupole GC-MS equipped with a silicone membrane separator operating under temperature programmed GC conditions was used to determine all CDDs. Instrumental calibration was accomplished by monitoring m/z 321.9 for a reference standard of 1,2,3,4-tetrachlorodibenzop-dioxin (1234-'I'CDD). Quantitative estimations in ng/g for pentachlorodibenzo-p-dioxins(PCDDs) monitored a t m / z 355.9, hexachlorodibenzo-p-dioxins(HCDDs) at m / z 389.9, heptachlorodibenzo-p-dioxins(H,CDDs) at m / z 425.8, and octachlorodibenzo-p-dioxin (OCDD) at m/z 459.7 were then determined in each sample using the response factor for 1234TCDD. These results are presented using two significant figures in the authors' Table II (2). Because CDDs of differing degrees of chlorination exhibit varying ionization efficiency, fractional abunclance of the monitored mass (3), mass-dependent nonlinear ion transmission through the quadrupole, and temperature-dependlent separator membrane transmission rates ( 4 ) , not only are the authors' reported data likely to be inaccurate but their proportions relative to TCDDs may also be incorrect. Although~the instrumental parameters mentioned affect quantitative accuracy for each of the CDD congeners differently, they would not be expected to significantly affect tho reproducibility of such data on a properly functioning GC-MS, as indicated by the authors' description of procedural reproducibility. During previous studies (5,6)we had conducted two simple experiments with a variety of CDDs which illustrate the nature and magnitude of the effects on CDDs quantitation accuracy arising from some of the GC-MS-SIM parameters mentioned. One experiment demonstrated that transmission efficiency of CDDs bearing different numbers of chlorine atoms through 0003-2700/82/0354-0823$0 1.25/0
Table I. Comparison of Relative Peak Ratios for CDDs through a Glass-Jet and Silicone Membrane Separator" re1 response no. of component. (I re1 std dev) replicates 123658-HCDD membrane jet
1.00 i 1.00 ''
... ...
1234658-H7CDDmembrane 0.34 z 0.04 jet
OCDD membrane jet
0.63 z 0.10 0.21 I0.05 0.38 I 0.04
7 4 7 4
I 1
All values normalized to HCDD response, see text for
conditions. a silicone membrane separator was variable and not necessarily predictable. In order to isolate the effect of the separator, we employed a Kratos MS-30 GC-MS equipped with a packed column (5),similar in characteristics to the authors' column, operated under isothermal conditions. A test standard containing 100 ng/mL each of 123678-HCDD, 1234678-H7CDD, and OCDD was used to show variations in separator transmission characteristics when all other conditions were held constant. The MS-30 GC-MS was operated under SIM conditions at low mass resolution (- 1500) and the parent ions defined by the authors were monitored. Initially, 3-pL injections of the test standard were examined by using a single-stage glass-jet separator maintained at 250 O C . Next, a silicone membrane separator (also maintained at 250 "C) was substituted for the glass-jet interface and the test standard reexamined. The GC-MS-SIM data from this experiment appear in Table I. Comparison of the relative responses by peak area for H7CDD and OCDD, to HCDD, characterizes the transmission behavior of the membrane vis-a-vis the jet for different CDD congeners. Since it is known that permeation of a given CDD decreases with increasing temperature for silicone membranes (4), the authors' responses for higher chlorinated CDDs relative to 1234-TCDD would be expected to show even greater deviations in transmission because the interface in a Hewlett-Packard 5992 is located inside the GC oven and was therefore subjected to temperature programming conditions (2). A second experiment illustrated the degree of quantitative bias for higher chlorinated CDDs associated with the use of a Hewlett-Packard 5992 GC-MS when calibrated as described by the authors (6). A single-stage glass-jet separator was installed along with a packed column (again similar to the authors') which was operated under tempeature programmed @ 1982 American Chemlcal Society
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Anal. Chem. 1982, 54, 824-825
Table 11. Area Response Factors of CDDs Relative to 1234-TCDD at m / z 32Za component
m/z
re1 response
( * re1 std dev)
no. of replicates
1234-TCDD 322 1.00 k 0.03 5 237 8-TCDD 322 0.89 i: 0.03 5 12378-PCDD 356 0.52 f 0.02 2 HCDD mixture 390 0.44 i 0.02 4 1234678-H,CDD 426 0.46 i: 0.01 3 OCDD 460 0.32 i: 0.01 3 a 100 pg of each component injected, see text for conditions. conditions. By use of analytical reference standards of 1234-TCDD, 2378-TCDD, 12378-PCDD, a mixture of two HCDD isomers, 1234678-H7CDD, and OCDD, GC-MS-SIM area responses were determined for 100-pg injections. The resulting response factors obtained for each CDD congener relative to the response of 1234-TCDD monitored at m , / 2 322 are presented in Table 11. Although these values are expected to differ from those exhibited by the authors' instrument, they do illustrate the possible margin of quantitative error which could be introduced via the assumption of a constant response factor of 1. In view of the described behavior for CDD congener transmiasion through silicone membrane separators, and the relative response factor data we have presented, it is very possible that the authors' CDD determinations (other than TCDDs) are biased low to a significant extent. Hence, the authors' compilation of these data in tabular, bar graph, and ratio formats (authors' Table 11, Figures 2 and 4, and Table
IV, respectively) should not be considered reliable as published. Although the primary purpose of our paper is to call attention to deficiencies in the authors' CDD determinations, certain unsubstantiated assessments involving chlorobenzene data also appear in their publication. These findings should be critically reviewed by an expert in GC-MS if abstracting for comparative purposes i s intended.
LITERATURE CITED (1) ACS Committee on Envlronmental Improvement Anal. Chem. 1980, 52, 2242-2249. (2) Elceman, 0. A.; Clement, R. E.; Karasek, F. W. Anal. Chem. 1981, 53, 955-959. (3) Mlllard, B. J. "Quantitative Mass Spectrometry"; Heyden: London, 1979; p 72. (4) Shadoff, L. A.; Hummel, R. A. Blomed. Mass Spectrom. 1978, 5 , 7-13. (5) Langhorst, M. I..; Shadoff, L. A. Anal. Chem. 1980, 52, 2037-2044. (8) Lamparskl, L. L.; Nestrick, T. J. Ana/. Chem. 1980, 52, 2045-2054.
T. J. Nestrick* L. L. Lamparski* W. B. Crummett L. A. Shadoff The Bow Chemical Company Michigan Division Analytical Laboratories Building 574 Midland, Michigan 48640
RECEIVED for review August 3, 1981. Accepted January 11, 1982.
Mass Spectrometric Sensitivity Data for Low Voltage Electron Impact Ionization of Alkylpyrenes Sir: Over the last 30 years, mass spectrometry has been used for qualitative and quantitative analysis of mineral oil fractions. The generation of unfragmented molecule ions by low voltage electron impact has proved to be particularly suitable for this purpose. However, the relative sensitivities of this method to the various molecules present in the complex oil mixtures usually found in the refining industry must first be determined. Lumpkin (I), Crable, Kearns, and Norris (2),Lumpkin and Aczel(3), and Shultz, Sharkey, and Brown (4) quote sensitivity data for the low voltage electron impact method for olefins, various substituted benzenes, aromatics, naphtheno aromatics, and heterocyclic compounds. On the basis of sensitivity values for aromatics and naphtheno aromatics, Severin, Bergmann, and Oelert (5) have derived empirical rules to extrapolate from these values onto unmeasured substances. The majority of these values were obtained from measuring substances without alkyl groups. However, mass spectrometric investigation of high-boiling oil and liquified coal fractions has shown that by far the majority of the components present in the mixture are alkylated ( 5 , 6 ) . Unfortunately, samples of such alkylated components are very difficult to obtain commercially, and thus the development of this analytical method has had to be based up to now on "model components" which represent a very insignificant portion of oil mixtures in commercial practice. As a partial solution to this problem, more relevant to the analysis of liquified coal products, Schiller investigated aromatic systems with up to six methyl groups (7). 0003-2700/82/0354-08!24$01,25/0
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Table I. Calibration Mixture of Alkylated Pyrenes (in n-Hexane) weighed abunmass, portion, dance, component amu mg mol% pyrene
Lme thylpyrene 1-ethylpyrene 1-propylpyrene 1-butyl pyrene 1-pentylpyrene 1-hexylpyrene 1-hexadecvlwrene
202 21 6 230 244 258 27 2 286 426
18.90 11.38 9.50 12.44 9.70 10.06 10.53 8.30
25.33 14.26 11.18 13.80 10.18 9.92 9.97 5.27
Up to now, no systematic work has been done on the influence on sensitivity of the alkyl chain length in larger aromatic ring systems. In addition to this, it has previously not been possible to estimate the changes that must be made to the empirically determined rules with variation in the electron impact energies. For this reason, based on the alkylpyrenes, we have determined the dependency of sensitivity on the alkyl chain length for a number of different ionization energies.
EXPERIMENTAL SECTION Samples. Pyrene and 3-methylpyrene were obtained from the Rtitgers Co., 4620 Castrop-Rauxel, Germany. The higher homologues (Table I) were then synthesized in a two-stage process using Friedel-Crafts acylation with the appropriate acid chloride, followed by reduction of the ketone via a Wolff-Kishner reaction. The impurities arising in this synthesis can be ignored. 0 1982 American Chemical Society
