Anal. Chem. 1991, 63,2697-2705 Cohen. A. S.; Paulus, A.: Karger, E. L.Chromtobvephie1987, 2 4 , 15. Paulus, A.; Gessmann. E.: Field, M. J. Electrophoresis 1990, 1 1 , 702. Yang, F. M C 8. CC. Commun. 1981. 4 , 83. Bruno. A. E.; Paulus. A.: Eornhop. D. J . Appl. Spectrosc. 1991, 45, 462. Dovichi. N. J. Rev. Sci. Insrrum. 1990, 67 (12). 653. Bruno, A . E.: Gassmann, E.: Pericles, N.; Anton, K. Anal. Chem. 1989. 6 1 , 876. Gassmann. E.; Kuo, J. E.: Zare. R. N. Sclence 1985. 230, 813. Liu. J.; Shirota. 0.;Novotny. M. Anal. Chem. 1991, 63, 413. Dovichi. N. CRCCrit. Rev. Anal. Chem. 1987, 17, 357. Eornhop. D. J.; Dovichi. N. J. Anal. Chem. 1986. 5 8 , 504. Eornhop. D. J.; Dovichi. N. J. Anal. Chem. 1987. 5 9 , 1632. Bomhop, D. J.; Nolan. T. G. Dovichi, N. J. J . Chromatogr. 1987. 384, 181.
Synovec, R. E. Anal. Chem. 1987, 59. 2877. Chen, C. Y.; Demana, T.; Huang, S. D.; Morris, M. D. Anal. Chem. 1989, 6 1 . 1590. Pewiisryn, J. Anal. Chem. 1988, 60, 2796. Pawiiszyn, J. Spectrochim. Acta Rev. 1990, 73, 354. Hoffstetter-Kuhn, S . ; Paulus, A.; Gassmann, E.; Widmer, H. M. Anal. Chem. 1991, 63, 1541. Honda, S.; Iwase, S.; Makino, A.; FuJiwara,S. Anal. Biochem. 1989, 176, 72. Garner, T. W.; Yeung, E. S. J . Chromatogr. 1990, 515, 639. Nardi, A.; Fanail, S.; Foret, F. Electrophoresls 1990, 1 1 , 774. Churms, S . C. J . Chromatogr. 1990, 500, 555. Eettier, E.; Amado, R.; Neukom, H. J . Chromatogr. 1990, 498, 213. Scher, H. Electrophoresls 1990, 1 1 , 16. Ai-Hakim, A.; Linhardt, R. Nectrophoresis 1990, 1 7 , 23.
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(33) Marcuse, D. I n Principles of Optical Fiber Measurements; Academic Press: New York, 1981. (34) Born, M.; Wolf, E. I n principles of Optics; Pergamon Press: New York. 1989. (35) Knox, J. H. Chromatographla 1988, 2 6 , 329. (36) Jones, E. J.; Grushka, E. J . Chromatogr. 1989, 466, 219. (37) Grushka, E.: McCormick. R. M.; Kirkland, J. J. Anal. Chem. 1989, 61, 241. (38) Gobie, W. A.; Ivory, C. F. J . Chromatogr. 1990, 576, 191. (39) Vinther, A.; Sieberg, H. J . Chromatogr. 1991, 559, 27-42. (40) Nelson, R. J.; Paulus, A.; Cohen, A. S.; Guttman, A,; Karger, E. L. J . Chromatogr. 1989, 480, 111. (41) Hamamatsu. Technical note TN-102, 1982. (42) United Detector Technology. Technical note The guide to position sensing. 1986. (43) Siebert, H. P. Sensoren 1 ; Elektronik 1988; 241, 34. (44) Renn, C. N.; Synovec, R. E. Anal. Chem. 1988, 60, 1168. (45) Yariv, A. I n Optkal Electronics, 3rd ed.; CDS College Publishing: New York, 1985. (46) Demtriider, W. In Laser Spectroscopy, Springer-Verlag: Berlin, 1982. (47) Huang. X.; Gordon, M. J.; Zare, R. M. Anal. Chem. 1988, 6 0 , 375. (48) Consden, T. W.; Stanier, W. M. Nature 1952, 169, 783. (49) Garner, T. W.; Yeung, E. S. J . Chromatogr. 1990, 515, 639. (50) Bruno, A. E. Eur. Pat. Appl. No. 67-17928, 1990. (51) Kurosu, Y.; Sasakl, T.; Saito, M. J . Mgh Resoiut. Chromatogr. 1991, 14, 86.
RECEIVED for review July 1, 1991. Accepted September 12, 1991.
Monobromopolychlorodibenzo-p-dioxins and Dibenzofurans in Municipal Waste Incinerator Flyash H. Y. Tong,’ S. J. Monson, and M. L. Gross* Midwest Center f o r Mass Spectrometry, Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304 L. Q. Huang The Connecticut Agricultural Experiment Station, 123 Huntington Street, New Haven, Connecticut 06504 Caplllary cdumn gas chromatographylhlgh-resolutlon mass spectrometry was used In two different selected-Ion monltorlng modes to analyze trace levels of monobromopolychlorodlbenzo-pdloxlns and dlbenzofurans (BPCDD/Fs) In munlclpal waste Inclnerator (MWI) flyash. The mass profile monltorlng mode Is well-sulted for ldentlflcatlon of unknown compounds In uncharacterlzed matrlces because lt has superlor dlagnostlc capablllty. Owing to Its high sensltlvlty, conventional peak lop monltorlng was used to quantify, on the basts of polychlorodlbenzo-p -dloxln and dlbenrofuran (PCDD/F) standards, the BPCDD/Fs In the sample. The results were compared wlth those obtalned by using two commerclal BPCDDs as standards, and the latter results are 4 tlmes greater, Indicating the need for appropriate standards. The hlgh certainty and sensltlvlty obtalned from these two mass spectrometric techniques combined wlth the resolvlng power of caplllary gas chromatography enabled us to compare for the flrst t h e the Isomer dlstrlbutlon patterns between BPCDD/Fs and thelr PCDD/F analogues at a hlgh confldence level. The comparison lndlcates BPCDD/Fs and PCDD/Fs found In M W I flyash are closely related and that many BPCDD/Fs wlth a 2,3,7,8-substltutlon conflguratlon may be present In M W I flyash.
INTRODUCTION The impact of polychlorinated dibenzo-p-dioxins and diCurrent.address: CIBA-GEIGY Corp., Analytical Research, 444 Mill River Rd., Ardsley, NY 10502.
Saw
0003-2700/9 110363-2697$02.50/0
benzofurans (PCDD/Fs) on the environment and human health has been of public and scientific concern during the last 15 years. The concern ismainly due to the considerable toxic effects of some PCDD/Fs (1, 2). Studies reveal that the general population of North America has an adipose tissue concentration of 5-8 ppt of 2,3,7,8tetrachlorodibenzo-p-dioxin(2,3,7,8-C14-DD,more commonly referred to as TCDD) (3-6). It has been proposed that flyash from municipal waste incinerators (MWI) is the major contributor (7, 8). Flyash is a fine particulate byproduct generated from MWIs. Because the use of refuse incineration worldwide is extensive, the quantity of flyash emitted into the environment is significant (8). More than 600 organic components have been found in flyash, and these compounds include aliphatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), polyhalogenated aromatic hydrocarbons (PHAHs), oxy-PAHs, nitro-PAHs, and sulfur-containing compounds (9, 10). PCDD/Fs appear to be the most hazardous of these emissions (7, 8). Planar PHAHs, like PCDD/Fs and polychlorobiphenyls (PCBs),elicit a variety of similar biological effects (11). These diverse biological responses are believed to arise from the altered gene expression, which is a consequence of the highaffinity, stereospecific binding of planar PHAHs to a soluble protein known as the Ah receptor (11-13). Probably owing to stereochemical factors, those planar PHAHs with a 2,3,7,8-substituted configuration are more toxic and persistent than other PHAHs (2,14,15). Such concerns about PCDD/Fs and PCBs have been naturally extended to the related polybromo or mixed bromo/chloro dibenzodioxins and furans 0 199 1 American Chemical Society
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(PBDD/Fs and Br/Cl-DD/Fs) (16). PBDD/Fs seem to have similar or even higher toxicity than the chloro analogues. It was reported that some biological activity of 2,3,7,8-tetrabromodibenzodioxin(2,3,7,8-Br4-DD) exceeds that of 2,3,7,8-C14-DD (15, 1 7 ) . Very recently, scientists have started to monitor environmental samples for PBDD/Fs and Br/Cl-DD/Fs. Low levels of PBDD/Fs were reported in commercial 2,4,64ribromophenol and tetrabromobiphenyl(18) as well as in flame retardants and related products (IO,19, 20). Currently, little is known about Br/Cl-DD/Fs. Structural considerations and biological activity of some isomers, however, indicate that their toxicity is similar to that of chlorinated analogues. Brominated compounds are important technical products used in a variety of applications such as gasoline additives, fumigants, flame retardants, drugs,sanitizing agents, and agrochemicals. Among these compounds, polybromobiphenyl (PBB) and polybromobiphenyl ether (PBBE) are important as flame retardants (16, 19). Often 10-20% (by weight) of PBB and PBBE are added to plastic, textiles, carpets, adhesive coatings, and other materials as fire retardants. Most of those products are eventually discarded, and significant quantities of these are incinerated. Therefore, it is reasonable to suspect that PBDD/Fs and Br/Cl-DD/Fs are formed as part of the flame chemistry in MWIs. This might be an important route for human exposure of such potential hazards. After 15 years of effort by many scientists, analysis of PCDD/Fs in various matrices has become well-established. The US.Environmental Protection Agency (US. EPA) has general guidelines for such analyses (21-23). In contrast, few studies have been reported for Br/Cl-DD/Fs. In the analysis of samples from an accidental fire, Buser (19) estimated that polybromodibenzofurans (PBDFs) and polybromodibenzodioxins (PBDDs) are at concentrations of 10-1570and 170, respectively, relative to their PCDF and PCDD analogues. Smaller quantities of Br/Cl-DD/Fs were also observed. Buser (24) used gas chromatography/negative-ion chemical ionization mass spectrometry (GC/NICIMS) with low resolution to monitor the Br ions at m/z 79 and 81 for bromo-containing PAHs. This is directed at screening sample extracts because the Br anion results from dissociative electron capture of most brominated molecules. Owing to the various responses from isomer to isomer (25-27), the NICIMS technique is not ideal for providing reliable information on quantification and isomer distribution patterns. Moreover, positive identification of Br/Cl-DD/Fs cannot be achieved solely on the basis of ions of m / z 79 and 81. Monobromopolychlorodibenzodioxins a n d furans (BPCDD/Fs) were detected by Schafer (28) in chimney residues of chemical waste incinerators. Very recently, we (29) and several other investigators (30-33) detected significant amounts of BPCDD/Fs in MWI samples. The primary difficulties in the analysis of trace amounts of BPCDD/Fs in flyash are the limited information on the properties of BPCDD/Fs and the extreme complexity of the flyash matrices. There are vast numbers of possible isomers and congeners of BPCDD/Fs, 44 different dibenzo-p-dioxin (DD) and dibenzofuran (DF) groups with different combinations of bromine and chlorine substitutions, and the total is greater than 5000 individual isomers. Among those isomers, more than 400 isomers have the 2,3,7,8-substitution, and they are suspected to be of high toxicity. In contrast, there are very few commercial standard compounds available because it is extremely difficult to synthesize and separate all the isomers. Moreover, hundreds and perhaps thousands of other organic compounds are present in flyash, many of which are PHAHs, and thus, severe interferences can be expected. Under such
circumstances, the analytical method must be capable of performing multicomponent analysis with high certainty and sensitivity. Capillary column gas chromatography/ high-resolution mass spectrometry (GC/HRMS) with electron ionization is currently the most likely method to meet such a challenge. Because the concentration levels of the target compounds are low, GC/HRMS is conventionally operated in the selected-ion monitoring (SIM) mode, while the peak top intensities of several characteristic ions of the target compounds are acquired at a mass-resolving power of ca. 10000. Although GC/HRMS-SIM-peak top monitoring can resolve interferences whose masses are separable from those of the target compounds at the mass-resolving power chosen, it suffers when interferences having masses nearly identical to those of the analytes are encountered. The ability to resolve closely related interferences is crucial for the successful BPCDD/F analysis in complex and uncharacterized matrices. In this paper, we report results from the analysis of MWI flyash for BPCDD/Fs by using GC/HRMS-SIM in both the mass profile and peak top monitoring modes. The mass profile method substantially improves the certainty for target compound identification, adds the capability of interference identification, and still provides detection limits at the lowpicogram level. Furthermore, the method allows one to investigate further any peaks on the mass chromatogram to see whether the elution is due to a single component or a mixture. The peak top monitoring mode was used for final quantification because the method affords a higher signal-to-n&e ratio ( S I N ) than does the mass profile monitoring. This and other investigations of BPCDD/Fs will be important for assessing health risks and the impact of BPCDD/Fs on the environment. Another reason for studying BPCDD/Fs in flyash is to provide data for developing mechanisms to explain the formation of PCDD/Fs in MWIs. Comparison of the isomer distribution patterns between BPCDD/Fs and PCDD/Fs found in the same flyash sample is made in this paper. The implications of BPCDD/Fs in the formation mechanism, however, will be discussed in a separate publication.
EXPERIMENTAL SECTION Chemicals and Flyash Sample. The native and %,,isotope were labeled PCDD/F standards as well as two BPCDD stanpurchased from Cambridge Isotope Laboratory (CIL), Woburn, MA. The native PCDD/F isomers included 1,2,3,4-C4-DD, 2,3,7,8-C&-DD,1,2,3,7,8-C&-DD,1,2,3,4,7&C&-DD, 1,2,3,6,7,8C&-DD, 1,2,3,7,8,9-C&-DD,1,2,3,4,6,7,8-C17-DD,and C18-DD; 2,3,7,SCb-DF11,2,3,7,&Cl,-DF,2,3,4,7,SCl,-DF, 1,2,3,4,7,8C&-DF, 1,2,3,7,8,9-C&-DF,1,2,3,4,6,'7&Cl,-DF,1,2,3,4,7,8,9-C1,-DF,and ClB-DF. The l3Cl2 isotope labeled PCDD/F standard included 2,3,7,8-Cld-DD, 1,2,3,7&Cl,yDD,1,2,3,6,7,8-C&-DD,1,2,3,4,6,7,8C1,-DD, and Cl,-DD; 2,3,7,8-C14-DF,1,2,3,7,8-C15-DF,2,3,4,7,8C15-DF, 1,2,3,4,7,8-C&-DF,and 1,2,3,4,6,7,8-C17-DF. The two BPCDD standards were 2-Br-3,7,8-C13-DD and 2Br-1,3,7,8-C14-DD,All solvents used in this study were at least HPLC grade and were purchased from Fisher Scientific. The MWI flyash used in this study was Ontario flyash received from Dr. Ray E. Clement, Ministry of Ontario Environment, Toronto, Canada. The sample was collected from the electrostatic precipitator of an MWI. The flyash sample was homogenized and then stored at room temperature away from light. Sample Preparation. A series of sample preparation and clean-up steps that have been used for PCDD/F analyses were applied to the BPCDD/F analyses. This procedure consisted of benzene extraction, pH wash, and multicolumn chromatographic separation prior to injection onto GC/MS. The details of this procedure were reported previously (34). The same fractions containing PCDD/Fs were used for BPCDD/F analyses. GC/HRMS Analysis. Two capillary column GC/HRMS
ANALYTICAL CHEMISTRY, VOL. 03, NO. 23, DECEMBER 1, 1991
systems were used for BPCDD/F analysis in flyash. At the Midwest Center for Mass Spectrometry, the system was a Carlo-Erba GC/Kratos MS-50 double-focusing mass spectrometer with a direct inlet GC/MS interface heated at 300 "C. Two capillary GC columns, 60 m and 30 m X 0.32 mm i.d. DB-5 columns (J & W Scientific),were used with on-column injection. The typical GC temperature programs were 80 "C (2 min) to 300 "C (10 min) at a rate of 10 "C/min for the 60-m column and 80 "C (2 min) to 300 "C (20 min) at a rate of 10 "C/min for the 30-m column. The mass spectrometer was operated in the E1 mode (70-eV, 500-pA emission), and the source temperature was 250 "C. The mass spectrometer was controlled by a custom-built multiple-ion detection (MID) system that allowed the specified number of ions (channels)to be monitored under computer control. The internal structure of the MID provided for full digital control of the electric sector and accelerating potential for each channel and the corresponding signal-processingparameters. The typical conditions were scan rate 0.1 s/mass window, amplifier bandwidth 1 kHz, and sweep width 300 ppm at 8ooo mass-resolving power. Six ions were often monitored as one group, and each group was sequentially changed during different analyte elution times. After an HRGC/HRMS run, the mass profile data for any peaks or group of peaks at any time or over any time range along a mass chromatogram could be recalled for further processing. The second system was a Hewlett-Packard 5890 GC/Kratos CONCEPT IS double-focusing mass spectrometer (at the Connecticut Agricultural Experiment Station). The GC conditions were: 60 m X 0.32 mm i.d. DB-5 column; temperature programmed from 200 "C (2 min) to 220 "C (16 min) at a rate of 5 "C/min, then to 235 "C (7 min) at a rate of 5 "C/min, and finally to 330 "C (5 min) at a rate of 5 "C/min; helium carrier gas at a head pressure of 20 psi; splitless injection at 275 "C; and direct GC/MS interface at 300 "C. The mass spectrometer was operated in the SIM mode with peak top monitoring. The magnet was switched when different ion groups were monitored during a run to achieve the maximum sensitivity. An EI-only source was used at a temperature of 250 "C. The filament configuration was modified to have both filament and trap at the same potential, so that electrons emitted from the filament were forced to travel back and forth in the ion source to enhance the ionization efficiency. The filament current was 500 pA in the emission stabilization mode. An electron multiplier at a gain of lo6,in combination with a post-acceleration detector at 8 kV, was used for ion detection. High-resolution (>lOOOO, 10% valley definition) mass chromatogram data obtained by peak top monitoring were used for compound identification and quantification.
RESULTS AND DISCUSSION A sample of municipal waste incinerator flyash was analyzed for BPCDD/Fs by using two HRGC/HRMS systems. The system at the University of Nebraska is better suited for identification of the BPCDD/Fs because it acquired data in the mass profile mode. A second and newer system a t the Connecticut Agricultural Experiment Station was used for quantification because it has better magnet control so that analytes of widely different masses could be monitored by magnet field switching. Quantification was performed in the faster scanning peak top monitoring mode so that higher SIN chromatographic peaks were obtained. Identification of BPCDD/Fs in Flyash. There are strong similarities in structure and polarity of BPCDD/Fs and PCDD/Fs. Therefore, one can expect that those two types of compounds have similar chemical behavior in the sample clean-up procedure. In our preliminary study (29), BPCDD/Fs eluted into the same fraction as PCDD/Fs in both HPLC and multistep open-column chromatography clean-up procedures. This is consistent with the observations reported by Buser (24)and Sovocool(30). Consequently, in the present study, the fraction containing PCDD/F after sample preparation and clean-up was subjected to analysis for BPCDD/Fs. Identification of BPCDD/F in flyash involves some typical problems encountered with complex environmental sample
2890
Table I. GC Retention Time Windows and Concentration of PCDD/Fs and BPCDD/Fs Measured in Flyash compd
no. of possible isomers
retention time window, min
concn, ppb
Cld-DF Cld-DD BrCl,-DF BrC13-DD Clb-DF CIb-DD BrCl,-DF BrCl,-DD CkDF Cb-DD BrC15-DF BrC15-DD Cl7-DF C17-DD BrCe-DF BrCb-DD ClB-DF Cla-DD BrCl,-DF BrC1,-DD
38 22 140 70 28 14 140 70 16 10 84 42 4 2 28 14 1 1 4 2
15:20-22:50 17:OO-23:00 21:10-26:35 21:30-2810 2320-31:30 25:45-31:20 30:30-35:50 31:OO-37:00 33:55-39:25 35:20-38:55 3820-43:OO 39:20-42:30 42:30-43:50 42:OO-4420 4450-47:oo 4510-46:30 47:06-47:26 47:02-47:22 4945-5O:lO 4940-5O:lO
135 104 5 4, 16O 170 219 6 6, 25b 692 642 15 17 487 429 20 16 26 491 1 13
Quantified by using 2-Br-3,7,8-C13-DD. bQuantified by using 2-Br-1,3,7,8-C14-DD. analysis. First, there is a very large number of BPCDD/F isomers (see Table I) but few commercially available standard compounds. On the basis of the close relationship between BPCDD/Fs and PCDD/Fs, we have an expectation for the elution time range of BPCDD/Fs. The exact retention time range, however, cannot be established without appropriate standards. Second, the low concentration of BPCDD/Fs (expected to be a t least ten times lower than those of the PCDD/Fs) prevents the use of full-scan mass spectra for each GC peak identification. Third, the flyash matrix is extremely complex and contains a t least several hundred organic compounds. Many of those are other PHAHs that coelute in the various chromatography stages. Some potentially interfering compounds for the analysis of BrC13-DF in flyash are given in Table 11. For example, the relative abundance of C15-DFat m/z 347.8490 is only 0.2% with respect to the most abundant [M + 21 ion of C1,-DF, but interference with the molecular ion monitoring of BrC13-DF is likely to occur because the concentration of Cl,-DFs is usually higher than those of BrC13-DF and the elution time windows of BrC13-DFand C15-DF are overlapping. C15-DDs also elute in this retention time uindow, and their abundant molecular ions may create problems for measurement of the [M 61 ion of BrC13-DF. It may be better to monitor selectively [M + 21 and [M 41 ions for BrC1,-DF analyses. This type of choice may be further complicated if the 13C12-labeledauthentic PCDD/Fs are added to the sample as internal standards. In the case of monitoring the m f z 349.8487 and 351.8459 ions for BrCl,-DF, the [MI and [M + 21 ions of l3CI2-Cl5-DFneed to be resolved by either chromatographic means or high mass-resolving power. The potential interference from high concentrations of PCDD/Fs, illustrated above for BrC1,-DF, applies generally to other BPCDD/F analyses and must be carefully evaluated before selecting proper ions for BPCDD/F analyses. More serious interference problems are generated by the large number of uncharacterized PHAHs, for which information about structure, concentration, and elution times are not available. Some compounds in Table I1 can be distinguished from the target analby their characteristic isotopic pattern. If target compound amounts are low and the mass spectrometer is operated at high sensitivity, however, the pattern actually observed may deviate from theory. Because
+
+
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ANALYTICAL CHEMISTRY, VOL. 63, NO. 23, DECEMBER 1, 1991
Table 11. MS Data for BrC13-DF and Potential Interferences re1 differentiation intensa by MSb
compd
mas
ion
BrC13-DF (target analyte)
347.8511 349.8487 351.8459 353.8440 347.8490
M M+2 M+4 M+6 M + 10
0.51 1.00 0.66 0.18 0.002
M M+2 M M+2 M+4 M M+2 M+4 M+6 M M+2 M+4 M M+2 M+4 M+8 M M+2 M+6 M+8
0.61 1.00 0.60 1.00 0.66 0.61 1.00 0.65 0.22 0.51 1 .00 0.66 1.00 0.65 0.18 0.01 0.61 1.00 0.33 0.06
353.8576 355.8547 349.9031 351.9001 353.8971 Cl,-anthracene/ 347.8834 phenanthrene 349.8805 351.8777 353.8750 349.8667 BrC13-diphenyl 351.8643 ether 353.8617 347.8693 BrCI,-fluorene 349.8668 351.8641 353.8619 351.8783 &-xanthene 353.8754 BrC1,-naphthalene 347.8093 349.8065
I A
IRM HR (170000) IRM. SDI. HR (26000) IRM HR (7000) IRM HR (11000) m/z 349.8803
IRM HR (20000)
B
I
IRM HR (20000)
I
"z347.8826
I
IRM HR (10000) IRM HR (8000)
Differentiation by mass a Normalized to the most abundant ion. spectrometry can be accomplished by isotope ratio measurement (IRM), by selection of different ions (SDI) to be monitored, or by high-resolution (HR) monitoring (the required mass resolving power is given in parentheses).
the patterns of bromo/chloro compounds often resemble those of more highly chlorinated analogues (24), their utility is diminished. The primary criteria for the identification of PHAHs are correct mass, isotope ratio, and retention time. Owing to the difficulties associated with the last two criteria, accurate mass measurement of the characteristic ions is essential for positive identification of BPCDD/Fs in flyash. For such low-concentration analyses, GC/HRMS is almost universally operated in the SIM mode with peak top monitoring. That is, the mass spectrometer is tuned to detect the top of a given ion peak that is being measured. The certainty of identifications based on mass chromatogram data depends highly on the MS resolution employed. Thus,resolving powers of ca. 10 000 are used for typical PCDD/F analyses. When the sample matrices are not completely characterized and the potential interferences cannot be fully anticipated, a higher mass-resolving power is desired to minimize the possibility of a false identification. A mass-resolving power of greater than 20000, however, is difficult to use for analysis of trace analytes because the sensitivity is decreased and the demand on instrumental performance is high. Furthermore, it is difficult to choose a proper mass-resolving power in advance because the mases of interferences and the required resolution to isolate them are not known. GC/HRMS-SIM operated in the mass profile mode, as utilized in this laboratory (35), provides the capability of further investigating any mass chromatographic peak in the three dimensions of mass, time, and intensity. During a run, the mass profiles for each monitored ion are acquired in addition to the conventional mass chromatographic data. After a run, the mass profile data for any time point on the mass chromatogram can be recalled for further study. These features allow one to confirm the target analytes, to detect interferences, to recognize multiplets, and even to identify nontarget compounds by investigating the mass profile shape, centroid position, and their changes during the chromatographic process. Because of its versatility, this technique was used to identify the BPCDD/Fs in flyash. Some typical
C
t
I
I
'
I
I I
I
m/z 347.8510 349.8483 351.8451 Representative mass profile data of three groups of chromatographic peaks obtained during monitoring of BrCI,-DF in flyash extract. (A) BrCI,-DF, the theoretical and observed isotope ratios of m / z 348, 350, and 352 are 0.51:1.00:0.65and 0.51:1.00:0.66, respectively. (B) Tentatively identified as pentachloroanthracene/phenanthrene, the theoretical and observed isotope ratios of m l z 348,350, and 352 are 0.61:1.00:0.65and 0.65:1.00:0.68respectively. (C) More than one compound is present. Figure 1.
examples are illustrated in Figure 1. The mass profiles shown in Figure 1 represent three types of compounds that simultaneously appear on the three mass chromatograms for BrCl,-DF. The mass profiles in (A) show the correct mass and isotope ratio for three ions of BrC13-DF. The chromatographic retention time of the compound giving these ions is within the retention time range anticipated for the target compounds. Therefore, the chromatographic peak is attributed to BrC1,-DF. The compounds yielding the mass profiles in (B) eluted slightly later than BrC1,-DF, but they yield molecular ions having the correct isotope ratio of BrC13-DF. Because standards are not available and 140 possible isomers for BrC13-DFpotentially exist, we cannot set the retention window for BrCl,-DF precisely. On the basis of mass chromatographic
ANALYTICAL CHEMISTRY, VOL. 63, NO. 23, DECEMBER 1, 1991
data (peak top monitoring), the possibility, therefore, cannot be excluded that these peaks are from the target compounds. On the other hand, the mass profile data clearly indicate that the peaks are not from the target compounds because the mass centroids deviate from the expected masses. The deviation of the mass centroid allows us to calculate the accurate masses for those ions, which are given in Figure 1. These unexpected compounds should have similar structures to those of the target compounds because both types of compounds coeluted during the clean-up procedure and have similar capillary column GC retention times. On the basis of this knowledge and the elemental composition information derived from accurate mass measurements and abundance ratios, the compounds in mass profile B are tentatively identified as pentachloroanthracene/phenanthrene. In the SIM peak top monitoring mode, a mass resolving power of greater than 11OOO is required to eliminate the interference from pentachloroanthracene/phenanthrene on the mass chromatograms. The mass profile data in (C) illustrate the integrated profiles of one chromatographic peak appearing within the GC retention time window monitored for BrC13-DF and show that this peak actually is due to more than one compound, none of which is the target compound. The mass profile mode in this study was operated a t a mass-resolving power of 8OOO. We were able to detect a mass shift of 6 ppm, which corresponds to an interference that requires a mass-resolving power of 170 OOO for adequate separation by the conventional MS-SIM-peak top monitoring. Therefore, all the potential interferences listed in Table I1 can be diagnosed by using MS-SIM-mass profile monitoring. The third criterion for identification, the correct retention time, cannot be strictly judged because sufficient standards are not available. For all the mass chromatographic peaks that were attributed to BPCDD/Fs in this study, the accurate mass and isotope ratio measurements were taken from the mass profile data of three ions in the molecular ion clusters of the target compounds. A majority of the observed peaks were identified positively as BPCDD/Fs, whereas others were attributed to interferences. The ions that provided the least interference were noted. All of the information compiled from the mass profile monitoring was used as a guide to quantify the analytes by peak top monitoring. The identification of two BPCDD congener groups was further verified by using available standards. Figure 2 shows the GC/HRMS chromatograms of BrC1,-DD for the flyash sample and BPCDD standard runs. The position of 2-Br3,7,8-C13-DDis indicated by the retention time of the authentic standard (Figure 2A). This compound is the only isomer with a 2,3,7,8-substituted configuration in the BrC13-DDcongener group and has a particular importance in epidemiology studies because its counterpart, 2,3,7,&C14-DDis extremely toxic. The resolution of the chromatography is acceptable as indicated by the mass chromatogram of C14-DD (Figure 2D). The GC program is normally used for PCDD/F isomer specific analysis, by which the majority of PCDD/Fs with a 2,3,7,8substitution pattern can be separated from other isomers. The 2-Br-3,7,8-C13-DDwas not separated from its other isomers because there are more BrC13-DD isomers than C14-DDisomers. A similar phenomenon can also be seen in Figure 3, where the mass chromatograms of BrCl,-DD and CIS-DD are displayed. The elution time of 2-Br-1,3,7,8-C14-DDis indicated by that of the authentic standard (Figure 3A). BrC1,-DD may exist as five possible positional isomers with a 2,3,7,8-substituted configuration compared to a single isomer of its counterpart, 1,2,3,7,8-C15-DD,which is also marked on the Cl5-DD chromatogram (Figure 3D). The isomeric complexity
2701
A
B BrCIpDD, [M+4]
C BrC13-DD9[M+2] 10
111
E
9
13C1zClq-DD Std.
A
I\
BrCleDD Std.
JL
\
B BrClq-DD, [M+4]
"A BrClq-DD, [M+2]
il
E I
1
I
2612
l
l
13C1rC1yDD Std. I
,
29:26
I
,
,
I
,
3241
3556
l
l
,
3911
Retention Time ( min )
Flgure 3. HRGC/HRMS selected-iin chromatograms of ftyash extract: (A) [M 21 ion of a separate run of 2-Br-1.3,7,&C14-DD standard; (B and C) [M + 21 and [M + 41 ions of BrCI,-DD; (D) [M -+ 21 ion of CI,-DD (individual isomers: (1) 1,2,4,6,8-,1,2,4,7,9-,(2) 1,2,4,6,9-, (3)
+
1,2,3.6,8-, (4) 1,2,4,7,8-, (5) 1,2,3,7,9-, (6) 1,2,3,6,9-, (7) 1,2,4,6,7-, 1,2,4,8,9-, (8) 1,2,3,4,7-,(9) 1,2,3,4,6-, (10) 1,2,3,7,8-,(11) 1,2,3,6,7-, (12) 1,2,3,8,9-C15-DD); (E) [M 21 ion of the '3C,z-1,2,3,7,8-CI,-DD internal standard. Each chromatogram reflects the actual retention time under the same HRGC/HRMS conditions.
+
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ANALYTICAL CHEMISTRY, VOL. 63, NO. 23, DECEMBER 1, 1991
Table 111. Selected Ions Monitored for BPCDD/Fs in HRGWHRMS-SIM with Peak-Top Monitoring Mode
analyte BrC13-DF BrCI,-DD BrCl,-DF BrCl,-DD BrCIS-DF BrClS-DD BrCls-DF BrC1,-DD BrCI7-DF BrC17-DD
ion monitored,
m/z
isotope ratio (*acceptable variation)
351.8451, 349.8481 367.8400, 365.8430 385.8062, 383.8092 401.8011, 399.8041 417.7703, 419.7673 433.7652, 435.7622 451.7314, 453.7284 467.7263, 469.7233 489.6871, 487.6897 505.6820, 503.6847
0.65 0.10 0.65 f 0.10 0.84 f 0.10 0.84 0.10 0.98 f 0.10 0.98 f 0.10 0.84 0.10 0.84 f 0.10 0.76 f 0.10 0.76 f 0.10
A
A
*
* *
of BrC14-DDmakes monitoring for it more complicated than for the corresponding C15-DD. The retention time windows of PCDD/Fs and BPCDD/Fs under the GC conditions used are shown in Table I. Those data indicate that the retention times of the BCPDD/Fs are very regular, showing smooth increases in relative retention time with the increasing number of substituents. Buser (24) reported that one bromine atom increases the retention time nearly as much as do two chlorine atoms. Our data, however, indicate that one bromine atom increases the retention time approximately as much as do one and a half chlorine atoms. This is consistent with the observation reported by Sovocool et al. (30). Quantification of BPCDD/Fs in Flyash. Conventional GC/HRMS-SIM with peak top monitoring was used for quantifying BPCDD/Fs in the flyash. Table I11 lists the BPCDD/F ions and their theoretical abundance ratios used in the analyses. Some abundant ions of BPCDD/Fs are not on this list because high levels of those PCDD/Fs mentioned earlier will interfere. The isotope dilution method was used to measure BPCDD/F concentrations in the flyash sample (23). Owing to the absence of a full range of authentic BPCDD/F standards and the high similarity between BPCDD/Fs and PCDD/Fs, native and 13C12-labeledPCDD/F standards were employed for BPCDD/F quantification. For example, the relative response factor (RRF) of C14-DDdetermined by using native and 13C12-2,3,7,8-C14-DD standards was used for the quantification of BrC13-DDin the flyash sample. This RRF was then compared to that obtained from measurements of all the native BrC13-DD and the fortified 13C12-2,3,7,8-C14-DD in the same flyash extract (refer to Figure 2; the ratio of the sum of all signals due to BrC13-DD isomers to that of the l3CI2-2,3,7,8-C1,-DDisomer was calculated). This approach to BrC13-DD quantification was also applied to the determination of other BPCDD/Fs in the flyash. Therefore, the results listed in Table I should not be viewed as highly accurate. The assumptions for this quantification procedure are that (a) Cl,-DD and BrC13-DD have the same recoveries under the sample preparation procedures and (b) C14-DDand BrC13-DD have the same response factor. Similar recoveries of those two compound families were previously reported (24,29,30). The recoveries of 16 13C12-labeledPCDD/F standards spiked in this flyash were in the range 85-98%. The latter assumption (b) has not been verified and is obviously an approximation. The two available authentic standards, 2-Br3,7,8-C13-DDand 2-Br-1,3,7,8-C14-DD,were used to estimate the accuracy of the quantification procedure. Those results are given in Table I. The MS response factors of C4-DDand BrC13-DD,and CIS-DD and BrC14-DD,are different by a factor of 4. The levels of BPCDD/Fs measured in this flyash are approximately 4% of those of PCDD/F analogues. The actual
B
A
,L
, I1 BrClTDD , , -__-
..
Retention Time (min)
Figure 4. HRGCYHRMS selected-kn chromatograms of flyash extract. m l z values: [A(I)] 443.7401; [A(II)] 487.6897; [B(I)] 459.7350; [B(II)] 503.6847. The actual retention time windows for each chre matogram are given in Table I.
concentrations of BPCDD/Fs are higher if the BPCDD/Fs’ response factors are used in the determination. This is consistent with the published finding that levels of organic bromo compounds are 1-15% of those of the organic chloro compounds present in waste (24, 28). Distribution of Isomers of PCDD/F and BPCDD/F. High certainty and high sensitivity obtained from the MS techniques used, combined with the separation power of capillary column GC, enable us to compare the isomer distribution profiles of BPCDD/Fs and their PCDD/F counterparts found in the same flyash sample. For the purposes of comparison, we will define a BPCDD/F to be a counterpart of a PCDD/F if a bromine has replaced one chlorine. All the possible isomers of PCDD/Fs are believed to be present in MWI flyash ( 7 , 3 6 ) . It was observed that there is a remarkable similarity of PCDD/F isomer patterns among flyash from different countries (36). The distribution patterns for both PCDD/F and BPCDD/F are pertinent for evaluating current theories for how these materials are produced in MWI, and, therefore, some analysis of these patterns is given here. First, we compare the isomer distributions plotted in Figure 4 for C18-DD and BrC17-DDas well as those for C18-DF and BrC17-DFbecause the situation in terms of isomer content is simplest here. Note that the one C18-DD isomer has two BrC17-DD isomers as counterparts (Figure 4B), which is the theoretical maximum. Three BrC17-DF isomers out of a theoretical maximum of four are detected along with the single C18-DF isomer (Figure 4A). We cannot rule out coelution, however. Next, we consider the isomer distributions for C14-DD, C14-DF,C1,-DD, C1,-DF, and C16-DFand the corresponding monobromo analogues in which one of the chlorine atoms is replaced by bromine (see Figures 2,3, and 5). The potential isomer complexity is immense for these congeners. We are able to detect 15 at least partially separated chromatographic peaks for C14-DDout of a theoretical maximum of 22, indicating that the chromatography is reasonably optimum (Figure 2D). Only a small fraction of the 70 total possible BrC13-DD isomers is detected, however (Figure 2B,C). For Cl,-DD, 12 peaks of a maximum of 14 are seen (Figure 3D). As for
ANALYTICAL CHEMISTRY, VOL. 63, NO. 23, DECEMBER 1, 1991 0 2703 1
7
I!
B
n
d (
C CI7-DD
i i
J
M
Retention Time (min) Flgure 5. HRGClHRMSselected-ton chromatograms of flyash extract. [A(I)] [M 21 ion of C14-DF. Peak 1 contalns seven isomers Including 2,3,7,8CI4-DF. (A(II)] [M 21 ion of BrCi3-DF. [B(I)] [M 21 ion of CI,-DF. Peak 1 contains two isomers including 1,2,3,7,8-Ci5-DF; peak 2 contains four isomers Including 2,3,4,7,8-C15-DF. [B(II)] [M 21 ion of BrCi4-DF. [C(I)] [M 21 ion of CI,-DF. Peak 1 contains two isomers including 1,2,3,4,7,8cie-DF;peak 2 contains two isomers including 1,2,3,6,7,8-CIe-DF;peak 3 contains two isomers including 2,3,4,6,7,8-CI,-DF; peak 4 Is 1,2,3,7,8,9CI,-DF. [C(II)] [M 41 ion of BrCI,DF. The actual retention time window for each chromatogram is given in Table I.
+
+
+
+
+
+
C4-DD, some coelutions are known to occur, and they are identified in Figure 2. If all the BrC1,-DD were formed and eluted separately, 70 peaks would be seen; instead less than 50% of the maximum number can be observed (Figure 3B,C). The patterns of dibenzofuran isomers for C14-DF,CIS-DF, and C16-DFand their corresponding monobromo analogues show similar trends (see Figure 5). Although a majority of all the fully chlorinated isomers are detected, the fraction is much smaller for the monobromo analogues. There are theoretical maxima of 140, 140, and 84 isomers of BrC13-DF, BrC4-DF, and BrC15-DF, respectively, whereas less than 25% of the expected peaks are seen. Moreover, the peak patterns for a PCDD/F and its corresponding bromo analogue seem to be closely related. The data presented so far suggest that there is specificity manifested in the appearance of BPCDD/F isomers. Although we do not know the extent of coelution, it seems unlikely that it would be so extensive to account for the observed chromatograms. The case for specificity for BPCDD/Fs is made stronger by considering the C16-DD,C1,-DD, and C17-DFpatterns as well as those of the corresponding monobromo analogues (see
Retention Time (min) Fbure 6. HRGCCIHRMS selected-bn chromatograms of flyash extract: [A(I)] m l r 389.8158 (isomers: (1) 1,2,4,6,7,9-, 1,2,4,6,8,9-, (2) 1,2,3,4,6,8-, (3) 1,2,3,6,7,9-, 1,2,3,6,8,9-, (4) 1,2,3,4.6,9-, (5) 1,2,3,4,7,8-, (6) 1,2,3,6,7,8-, (7) 1,2,3,7,8,9-, 1,2,3,4,6,7-CI,-DD); [A(II)]mlr 435.7627; [B(I)] mlr 407.7820 (isomers: (1) 1,2,3,4,6,7,&, (2) 1,2,3,4,6,7,9-, (3) 1,2,3,4,6,8,9-, (4) 1,2,3,4,7,8,9-CI,-DF); [B(II)I m l r 453,7290; [C(I)] m l r 423.7769 (Isomers: (1) 1,2,3,4,6,7,9-, (2) 1,2,3,4,6,7,Bcl,-DD);[C(II)] mlz 469-7238. The actual retention time windows for each chromatogram are given in Table I.
Figure 6). Here, the isomer distributions are more tractable than those just discussed. For CITDD, both isomers are clearly resolved chromatographically (Figure 6C). Two groups of BrCb-DD isomers are also seen, but the number of chromatographic peaks is approximately 50% of the theoretical maximum. For Cl,-DF, all four isomers are seen, and they elute in two groups (Figure 6B). The corresponding BrC&-DF isomers also elute in two groups, but approximately only one-third of the maximum possible number of isomers is seen. The C16-DD isomers elute in three groups, and it is likely that all 10 isomers are present in the flyash sample (Figure 6A). The BrClb-DD isomers also elute in three groups, but the number of isomers is again significantly less than the theoretical maximum. The results of BPCDD/F and PCDD/F isomer pattern comparison support three conclusions. First, the BPCDD/F isomer distributions are simpler than those that would be expected by random substitution reactions and seem govemed by some specificity of formation. Second, BPCDD/F and PCDDIF in MWI flyash are closely related and may share similar formation mechanisms in MWI processes. Third, all the PCDD/F isomers with 2,3,7,8-substituted configuration are indicated in Figures 2-6. I t seems that many PCDD/F
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ANALYTICAL CHEMISTRY, VOL. 63, NO. 23,DECEMBER 1, 1991
isomers with the 2,3,7,&substitution configuration are present in MWI flyash on the basis of the relationship shown in the pattern comparison between PCDD/Fs and BPCDD/Fs. Isomer Distributions for Studies of Mechanism. Since PCDD/Fs were first found in MWI flyash in 1977 (37,38), many studies involving laboratory experiments and numerical modeling calculations have been focused on the mechanism of PCDD/F formation in the MWI. Different theories have been proposed (39-47), but most of them have not been extensively tested because it is difficult to simulate the complex flame chemistry of MWI in a laboratory-scale experiment. The precursors for PCDD/F formation and the mechanism of formation in the MWI still remain unclear. Studies of BPCDD/F in MWI flyash should facilitate mechanism development in this important field for the following reasons. First, chlorine and bromine have many chemical properties in common and probably share similar flame chemistries in halogen-DD/F formation. Therefore, information about each compound series is complementary. Second, in MWI feedstocks, the number of potential precursors for BPCDD/F formation is more limited than those for PCDD/F formation. Thus, possible precursors may be easier to identify. Third, when a bromine atom is placed on PCDD/F, the degree of structural symmetry is degraded and more isomers become possible (see Table I). The bromine atom in BPCDD/Fs may be viewed as a "label", and product analysis may provide additional mechanistic information on issues such as cyclization routes, substitution preferences, and sequence of reaction steps. More importantly, this "label" element participates in the formation mechanism under the real conditions of MWI, conditions that cannot be easily simulated. Finally, the higher molecular weights of BPCDD/Fs makes the analysis less ambiguous by lessening the general interference from PCB and polychlorobiphenyl ether (PCDPE) because of the longer retention times and higher masses of BPCDD/Fs. The difficulty with using Br as a "label" is that the large number of BPCDD/F isomers challenges the capabilities of modern gas chromatography. Summary. MWI flyash is an example of an environmental sample that contains low levels of isomerically complex analytes for which a complete set of authentic compounds and internal standards are not available. Furthermore, the sample also contains many potential interferences that have not been characterized. The results presented here serve to demonstrate the efficacy of GC/HRMS in both peak top and mass profile monitoring modes. Many BPCDD/Fs are present in the MWI flyash, and their levels are on average 25 times lower than their PCDD/F analogues. The results of BPCDD/F and PCDD/F isomer distribution pattern comparison reveal that (a) BPCCD/Fs and PCDD/Fs produced in MWI processes are closely related, (b) many BPCCD/Fs with the 2,3,7,8-substituted configuration may be present in MWI flyash, and (c) some specificity of formation governs the production of BPCDD/F isomers in municipal waste combustion. We propose that studies of BPCCD/Fs in MWI flyash will facilitate our understanding of the formation mechanisms of PCDD/Fs in MWI processes, and the implication of these isomer distributions for the mechanisms will be the subject of a future paper.
ACKNOWLEDGMENT We thank R. E. Clement of the Ontario Ministry of the Environment (Canada) for supplying the municipal incinerator flyash, B. P. Y. Lau of Health and Welfare Canada, and D. G. Patterson of the Center for Disease Control for helping in PCDD/F isomer identification and D. Hilker and S. Connor of the New York State Health Department for supplying some of the BPCDD/F standards. Registry No. C1,-DF, 30402-14-3; C14-DD,41903-57-5; Br-
C13-DF, 107227-56-5;BrClS-DD, 107227-75-8;Cl,-DF, 30402-15-4; CIS-DD,36088-22-9;BrC1,-DF, 109302-36-5;BrC14-DD,10926461-1; CI,-DF, 55684-94-1; Cl,-DD, 34465-46-8; BrC15-DF, 107103-81-1;BrC1,-DD, 109264-65-5;C17-DF,38998-75-3; C17-DD, 37871-00-4; BrC16-DF, 107207-47-6; BrC16-DD, 109264-67-7; Cl,-DF, 39001-02-0;Cl,-DD, 3268-87-9;BrC17-DF,109302-40-1; BrClTDD, 109264-69-9; 1,3,6,8C&-DD,33423-92-6; 1,3,7,9-C&-DD, 62470-53-5; 1,3,6,9-C1,-DD,71669-24-4;1,2,4,7-C&-DD,71669-28-8; 1,2,4,8-Cll-DD,71669-29-9; 1,3,7,8-C1,-DD,50585-46-1; 1,4,6,9Cld-DD, 40581-93-9; 1,2,4,6-Cl,-DD,71669-27-7; 1,2,4,9-C&-DD, 71665-99-1; 1,2,6,8-Cld-DD,67323-56-2; 1,4,7,&Cl4-DD,40581-94-0; 1,2,7,9-Cd-DD,71669-23-3; 1,2,3,4-Cld-DD,30746-58-8; 1,2,3,6Cld-DD, 71669-25-5; 1,2,6,9Cl,-DD, 40581-91-7; 1,2,3,7-C1,-DD, 67028-18-6 1,2,3,8-Cl,-DD,71669-25-5; 2,3,7,&C&-DD,1746-01-6 1,2,3,9-Cl,-DD, 71669-26-6; 1,2,7,8-CId-DD,34816-53-0; 1,2,6,7C&-DD,40581-90-6;1,2,8,9-Cl4-DD,62470-54-6;1,2,4,6,8-C&-DD, 71998-76-0; 1,2,4,7,9-C15-DD, 82291-37-0; 1,2,4,6,9-C1,-DD, 82291-36-9; 1,2,3,6,8-C1,-DD, 71925-16-1; 1,2,4,7,8-C1,-DD, 58802-08-7; 1,2,3,7,9-Cl,-DD, 71925-17-2; 1,2,3,6,9-C15-DD, 82291-34-7; 1,2,4,6,7-C1,-DD, 82291-35-8; 1,2,4,8,9-C1,-DD, 82291-38-1; 1,2,3,4,7-C1,-DD, 39227-61-7; 1,2,3,4,6-C&-DD, 67028-19-7; 1,2,3,7&Cl,-DD, 40321-76-4; 1,2,3,6,7-Cl,-DD, 71925-15-0; 1,2,3,8,9-Cl,-DD,71925-18-3; 2,3,7,8-Cl,-DF, 5120731-9; 1,2,3,7,8-C1,-DF,57117-41-6; 2,3,4,7,8-C&-DF,57117-31-4; 1,2,3,4,7,8-C1,-DF, 70648-26-9; 1,2,3,6,7,8-C&-DF,57117-44-9; 2,3,4,6,7,8-C1,-DF, 60851-34-5; 1,2,3,7,8,9-C&-DF,72918-21-9; 1,2,4,6,7,9-C&-DD,39227-62-8; 1,2,4,6,8,9-C&-DD,58802-09-8; 1,2,3,4,6,8-C&-DD,58200-67-2; 1,2,3,6,7,9-C&-DD,64461-98-9; 1,2,3,6,8,9-C&-DD,58200-69-+4;1,2,3,4,6,9-C&-DD,58200-68-3; 1,2,3,4,7,8-C&-DD,39227-28-6; 1,2,3,6,7,8-C&-DD,57653-85-7; 1,2,3,7,8,9-C&-DD,19408-74-3; 1,2,3,4,6,7-C&-DD,58200-66-1; 1,2,3,4,6,7&Cl,-DF, 67562-39-4; 1,2,3,4,6,7,9-C17-DF,70648-25-8; 1,2,3,4,6,8,9-ClT-DF,69698-58-4;1,2,3,4,7,8,9-C17-DF,55673-89-7; 1,2,3,4,6,7,9-Cl,-DD,58200-70-7;1,2,3,4,6,7&C&-DD,35822-46-9.
LITERATURE CITED Esposito, M. P.; Tiernan, T. V.; Dryden, F. E. Dioxins. EPA-600/2-80197; U S . GPO: Washington, DC, 1980. Rantanen, J. H.; Silano, V.; Tarkowski, S.; Yrjanheikki, E. PCBs, PCDDs and PCDFs : Prevention and Control of Accidental and Environmental Exposures; WHO: Geneva, 1987. Ryan, 2 . J.; Schecter, A.; Lizotte, R.; Sun, W. F.; Miller, L. Chemosphere 1985, 74, 929. Stanley, J. S.; Boggess, K. E.; Onstot, J.; Sack, T. M. Chemosphere, 1986. 15, 1605. Schecter, A.; Constable, J. D.; Arghestani, S.; Tong, H.; Gross, M. L. Chemosphere 1987, 16, 1997. Patterson, D. G.; Holler, J. S.; Lapeza, C. R., Jr.; Alexander, L. R.; Groce, D. F.; O'Connor, R. C.; Smith, S. J.; Liddle, J. A,; Needham, L. L. Anal. Chem. 1986, 58, 705. Karasek, F. W.; Hutzinger, 0. Anal. Chem. 1986, 58, 633A. Karasek, F. W.; Onuska, F. I. Anal. Chem. 1988. 5 4 , 309A. Tong, H. Y.; Shore, D. L.; Karasek, F. W. J. Chromatogr. 1984, 285, 423. Junk, G. A.; Ford, C. S. Chemosphere 1980, 9 , 187. Poland, A.; Knutson, J. C. Ann. Rev. Pharmacol. Toxicol. 1962, 22, 517. Whitlock, J. P., Jr. Ann. Rev. phsrmacol. Toxicol. 1986, 26, 333. Poland, A.; Glover, E.; Ebetino, F. H.; Kende, A. S. J. Biol. Chem. 1988, 267,6352. Rappe, C.; Marklund, S.; Kjeller, L. 0.; Bergqvist, P. A,; Hansson, M. I n Chbinated Dioxins and Dibenzofurans in the Total Environment I I ; Keith, L. H., Rappe, C., Choudhary, G., Eds.; Butterworth Publishers: Boston, 1985; p 401. Kende, A. S.; Wade, J. J. Environ. Health Perspecr. 1973, 5 , 49. Buser, H. R. Chemosphere 1987, 76, 713. Ramaiingam, 8.; Mazer, T.; Wagel, D. J.; Mallow, C. M.; Taylor, M. L.; Tiernan, T. V.; Garrett, J. H.; Rifkind, A. B. I n Chlorinated Dloxins and Dibenzoturans in Perspective; Rappe, C., Choudhary, G., Keith, L. H., Eds.; Lewis Publishers: Chelsea, MI, 1986; p 485. Thoma, H.; Rist. S.; Hauschulz, G.: Hutzinger, 0. Chemosphere 1986, 75,2111. Buser, H. R. Environ. Sd.Technol. 1988, 2 0 , 404. Donnelly, J. R.; Orange, A. H.; Nunn, N. J.; Sovocool, 0. W.; Brumley, W. C.; Mitchum, R. K. Biomed. Environ. Mass Spectrom. 1989, 78. 884. U.S. EPA, Analytical Procedures and Quality Assurance Plan for the AnaWsk of 2,3,7,8-TCDD in Tier 3 - 7 Samples of the U S .Environmental Protection Agency National Dioxin Study, EPA/600/3-85/019; U S . GPO Washington, DC. 1986. Midwest Research Institute. Guidelines for the Determination of Polyhalogenated Dibenzo -p -dioxins and Dibenzoturans in Commercial Products: Final Report to US. EPA (Contract No. 68-02-3938), 1985. US. Environmental Protection Agency. GPO: 7673: Tetra- through OCta-Chlorinated Dloxins and Fwans by Isotope Diluthn; U S . GPO: Washington, DC, July 1989.
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(40) zhiub, W. M.; Tsang, W. I n Human and Envkonmental Rlsks of Chbrinated Dioxins and Related compOunds; Tucker, R. E., Young, A. L., Gray, A. P., Eds.; Plenum Press: New York. 1983; p 731. (41) Shaub. W. M.; Tsang, W. Envkon. Sci. Technol. 1983, 77, 721. (42) Shaub. W. M.; Tsang, W. I n Chbrlnated Dioxlns and Dlbenrofwans /n the Total Envkonment II; Choudhary, G., Kelth, L. H., Rappe, C., Eds.; Butterworth Publishers: Boston, 1985; p 469. (43) Rghei, H. 0.;Eiceman, 0. A. Chemosphere 1985, 74, 167. (44) Dlckson. L. C.; Karasek, F. W. J . Chromtcgr. 1987, 389, 127. (45) Karasek, F. W.; Dickson, L. C. Science 1907, 237, 754. (46) Dlckson, L. C.; Lenoir, D.; Hutzinger, 0.;Naikwadi, K. P.; Karasek, F. W. ChemosDhere 1889. 79. 1435. (47) Altwicker, E. R.; Kumar, R.: Konduri, N. V.; Milllgan, M. S. Chemosphere 1980, 20, 1935.
RECEIVED for review April 1,1991. Accepted September 13, 1991. This was supported in part by the National Science Foundation (Grants CHE-8620177 and DIR-9017262).
Precise Determination of Femtogram Quantities of Radium by Thermal Ionization Mass Spectrometry Anthony S. Cohen* and R. Keith O'Nions Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, U.K.
Femtogram quantltles of mRa (-3 X 10' atoms, or 4 X lo4 Bq) have been determlned In environmental materials, Includlng seawater, mineral samples, and silicate rocks, by thermal ionlzatlon mass spectrometry. Chemlcai separatlon technlqws suitable for all these matedab are described here. Overall, these techniques enable the abundance of 22'Ra to be determlned in samples of both seawater and silicates whlch are some 10' tlmes smaller than those required by conventional radloactlve countlng methods.
INTRODUCTION The precise determination of Ra at the femtogram level is important in several disciplines ranging from isotope geochemistry to radiological protection. Chemical and mass spectrometric techniques have been described recently by Volpe e t al. (1) for the determination of small quantities of Ra (- 1 fg or 3 X lo6 atoms) in basaltic rocks. Thermal ionization mass spectrometry (TIMS) procedures, and appropriate chemical techniques, have also been developed in our laboratory for the measurement of small quantities (- 1 fg) of Ra. These have enabled us to measure the 2z6Ra abundance in as little as 35 g of seawater, as well as in a silicate mineral and basaltic rocks. Overall, the new techniques described below and in ref l offer considerable advantages over existing radioactive counting methods (2-5) which require sample sizes -lo3 times larger than those used here. The aims of this present contribution are (1) to describe our chemical methods for the extraction of Ra from environmental materials, including seawater and silicate rocks and minerals, in a form suitable for analysis by TIMS, (2) to provide details of the ion-counting TIMS requirements and methodology, (3) to present results on Pacific seawater, zircon (ZrSi04),and Icelandic basalt, and (4) to demonstrate that precise and repeatable results may be obtained.
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0003-2700/91/0363-2705$02.50/0
EXPERIMENTAL SECTION Apparatus. All beakers and vials used in this study were of PFA Teflon, cleaned for two -8-h periods in hot, high-purity 30% HN03, and washed with 18 MR deionized water. Ion-exchange columns were of two types. One type was of polypropylene (Poly-Prep columns supplied by BioRad Ltd.), with a resin capacity of 2 mL plus an integral reservoir of 10 mL. The second was made from heat-shrinkable PTFE with an i.d. of 3 mm, 0.15-mL resin capacity, and 1.5-mL reservoir. Both types of column were fitted with polyethylene frits. Reagents. Water and all acids were purified by subboiling distillation in quartz or PTFE stills. NH4EDTA(95%, from BDH L a . ) was prepared and cleaned as described in ref 1. It was then adjusted to pH 7.5 (solution A) and pH 8.94 (solution B) with high-purity NH3(aq). Specpure grade Na2C03and SrC03 and analytical grade Th(N03)4 were all from Johnson Matthey Chemicals PLC. The zzsRastandard (NIST 4953 D) is known to a precision of &0.8% (2 SE). Preparation of the 228RaSpike. The 228Raspike was produced by separating Ra directly from a solution of -200 mg of Th(N03), in -5 mL of 7 M HN03 by anion exchange. The purity of Th(N03)4was sufficiently high to render its initial cleanup unnecessary. The 228Raspike was calibrated against three accurately weighed aliquots of the 216Ra standard by isotope dilution TIMS; the three determinations agree to better than 0.5%. Initial Ra Separation (Seawater). The first stage separation of a Ra-Ba fraction from seawater is conveniently performed by coprecipitation rather than ion exchange. Sr, rather than Ba, was used for the coprecipitation of Ra for reasons discussed later. Seawater samples of -35 mL were weighed accurately in PFA beakers. The sample was spiked with z28Ra,and -0.1 mL of a -0.25 M Sr solution (in -1 M HCl) was added, followed by - 2 mL of concentrated H2S04. Sr(Ra)S04precipitated after the sample had been heated and allowed to stand for -8 h. The sample was then centrifuged, and the precipitate slurried in H20 and transferred to a 1.5-mL centrifuge tube. The precipitate was again centrifuged and the washinglcentrifuging process was repeated until the pH of the supernate was > -4. Conversion of Sr(Ra)S04to an acid-solublecompound is based on the classical Curie-Debierne method (6). The washed pre0 1991 American Chemical Society
