Anal. Chem. 1986, 58,2126-2129
2126
779-02-2; 1-methylanthracene, 610-48-0; 2-methylanthracene, 613-12-7;%methylphenanthrene,832-71-3;9-methylphenanthrene, 883-20-5;1-methylphenanthrene, 832-69-9;2-methylphenanthrene, 2531-84-2; 4,5-dimethylphenanthrene,3674-69-9;1,8-dimethylphenanthrene, 7372-87-4; 3,6-dimethylphenanthrene,1576-67-6; 9,10-dimethylphenanthrene,604-83-1; 1-aminoanthracene,61049-1; 9-aminophenanthrene, 947-73-9;fluorobenzene, 462-06-6; l&difluorobenzene, 540-36-3; 1,2-difluorobenzene,367-11-3; 1,3-difluorobenzene,372-18-9; 1,2,4-trifluorobenzene,367-23-7; 1,2,3-tritluorobenzene,1489-53-8;1,3,5trifluorobenzene,372-38-3; 1,2,4,5-tetrafluorobenzene, 327-54-8 1,2,3,5-tetrafluorobenzene, 2367-82-0; 1,2,3,4-tetrafluorobenzene,551-62-2; pentafluorobenzene, 363-72-4; hexafluorobenzene, 392-56-3; l-cyanonaphthalene, 86-53-3; 1-aminonaphthalene, 134-32-7; aniline, 62-53-3;fluorenone, 486-25-9; phenalen-1-one, 548-39-0;biphenyl, 92-52-4;p-xylene, 106-42-3;o-xylene, 95-47-6; 1-nitronaphthalene, 86-57-7;phenol, 108-952; m-xylene, 108-38-3;2-nitronaphthalene, 581-89-5; benzo[c]cinnoline, 230-17-1;toluene, 108-88-3;chlorobenzene, 108-90-7;cyanobenzene, 100-47-0;nitrobenzene, 98-95-3. LITERATURE CITED Slmonsick, W. J., Jr.; Hltes, R. A. Anal. Chem. 1984, 56, 2749-2754. Hecht, S. S.; Loy. M.; Hoffman, D. I n Carclnogenesls-A Comprehensive Survey; Jones, R. W., Freudenthal, R. I., Ed.; Raven Press: New York, 1976; Vol. 1, p 325. Wllson, E. W.; Pelroy, R.; Cresto, J. T. Mutagen Res. 1980, 79, 193-202. Mermelstein, R.; Kirlazides, D. K.; Butler, M.; McCoy, E. C.; Rosenkranz, H. S. Mutagen Res. 1981, 89, 187-196. Jennings, K. R. I n Gas Phase Ion Chemistry; Bowers, M. T.. Ed.; Academlc Press: New York, 1979; Vol. 2, p 123. Keough, T. Anal. Chem. 1982, 5 4 , 2540-2547.
Hammett. L. P. J. Am. Chem. Soc. 1837, 59, 96-103. Lowry, T. H.; Richardson, K. S. In Medrenkrm and Theory In Organic Chemlstry; 2nd ed.;Harper and row: New York. 1981; pp 113-225. Bursey, M. M. Org. Mass Spectrom. 1988, 7 , 31-46. Field, F. H. J. Am. Chem. Soc. 1980, 9 7 , 6334-6341. Levsen, K. I n Fundamental Aspects of Organic Mass Spectrometry; Wehheim: New York. 1978 pp 19-21. Tembreull, R.; Sin, C. H.; Ping, L.; Pang, H. M.; Lubman, D. M. Anal. Chem. 1984, 5 7 , 1186-1192. Jensen, T.; Kaminsky, R.; McVeety, E. D.; Woznlak, T. J.; H b s , R. A. Anal. Chem. 1982, 5 4 , 2388-2390. Dewar, M. J. S.; Thlel, W. J. Am. Chem. Soc.1977, 99,4894-4907. Fletcher, R.; Powell, J. J. D. Comput. J. 1983, 6 , 163-166. Hunt, D. F.; Gale, P. J. Anal. Chem. 1984, 56, 1111-1114. Cox, J. D.; Piicher, G. I n Thermochemlstry of Organlc and Organometallic Compounds; Academic Press: London, 1970. Brown, H. C.; Okamoto, Y. J. Am. Chem. SOC. 1958, 80, 4979-4987. Levin, R. D.; Lkrs, S. 0.Natl. Stand. Ret. Data Ser. ( U S . Natl. Bur. Stand.) 1982, No. 7 1 . Lau, Y. K.; Kebarle, P. K. J. Am. them. SOC.1858, 98, 7452-7453. Rosenstock, H. M.; Herron, J. T.; Draxl, K.; Steiner, E. W. “Energetics of Gaseous Ions”, J. Phys. Chem. Ref. Data Suppl. 1877, 6 , 1365. Hltes, R. A. Handbook of Mass Spectra of Envlronmental Contamlnants; CRC Press: Boca, Raton, FL, 1985; pp 84, 85, 188, 189. Dewar, M. J. S.;Thlel, W. J. Am. Chem. Soc.1977, 99,4907-4917. Ford, G. P.; Scribner, J. D. J. Am. Chem. SOC. 1981, 703, 428 1-4291. Mirek, J.; Buda, A. 2.Naturforsch ., A 1984, 39a. 386-390. White, C. M. I n Handbook of Po&cycllc Aromatic Hydrocarbons, Ed., Bjorseth, A,, Ed.; Marcel Dekker: New York, 1963; pp 525-616.
RECEIVED for review February 4, 1986. Accepted April 16, 1986. Supported by the U.S. Department of Energy (Grant NO. 80EV-10449).
Application of Particle Desorption Mass Spectrometry to the Characterization of Minerals W. R. Summers and E. A. Schweikert* Center for Chemical Characterization & Analysis, Texas A&M University, College Station, Texas 77843-3144
Four m h r a l specknerw were analyzed by parUcle desorption mass spectrometry using callfomlum-252 as the prbnary ion source. Poilucite, amblygonlte, mkrocllne, and IepMdlte, chosen for thek high alkatl metal content, were characterized wkh no apparent decrease In the extractlon fleld strength were thick and M a t l n g . Further, even though the samglven the very low bombarding ion thence, no complkatlons due to charge accurnrlatkn on the sample were encountered. Ouatitatlve resuits 0Wahed by PDMS were valklated by XPS, EYP, and SIMS. PDMS provldes for a rapkl, nondestructive determination of alkall metals In complex natural matrices wlth minimal sample preparation.
Geological materials represent a challenging case for surface characterization methods that employ charged particles as the probe or signal beam, due to their heterogeneity and insulating nature. Techniques currently applied in the analysis of geological specimens include SIMS, LAMMA, and especially EMP (I). Each of these techniques has strengths and limitations. EMP can provide quantitative data for elements of 2 2 11and with detection limits 20.1 atom % (2,3).SIMS and LAMMA both can provide isotopic and molecular information with detection limits as low as lo4 atom % (4).For geological specimens, SIMS is semiquantitative because the 0003-2700/86/0358-2126$01.50/0
yield of the secondary ions emitted is strongly matrix dependent (5). LAMMA is less prone to charge buildup problems since the probe beam consists of photons and the signal beam is of extremely low current; however, the sample spot addressed is destroyed in the analysis process (6-8). The present study examines the feasibility of applying particle desorption mass spectrometry for examining geological specimens. The method is based on the desorption of atomic and molecular species from surfaces bombarded by fast heavy ions (21 20; E 1 0.5 MeV/amu). This phenomenon was first observed by Macfarlane (9). Particle-induced desorption coupled with time-of-flight mass spectrometry (usually referred to as PDMS) has been applied successfully for the characterization of large involatile biomolecules (10,I1 1. In the realm of materials characterization, the application of PDMS in a microscopic mode has recently been discussed (12). The present paper presents the first results of PDMS applied on geological materials. The strong suits of PDMS are (a) the sample amount consumed is negligible and (b) the primary ion current required for PDMS is low; thus charge buildup and sample damage are avoided. This study like most PDMS work to date used as the beam of heavy ions the fission fragments from a low-intensity 252Cf source. The discrete nature (in time) of the fission event lends itself conveniently to time-of-flight mass spectrometry. This 0 1986 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 11, SEPTEMBER 1986
mass detection and identification mode allows simultaneous multimass, isotopespeciiic, elemental and molecular analysis. PDMS is a surface-sensitive technique. The sample depth probed, while varying with the nature of the matrix, appears not to exceed a few hundred A (13,14). The application of PDMS for bulk analysis requires, then, that surface contamination be controlled and kept to a minimum. Accordingly, this study was carried out in a UHV chamber. The PDMS experiment with a 262Cfsource is particularly well suited for UHV conditions. A compact setup can be devised featuring lo4 torr vacuum; a detailed description of this setup is given elsewhere (15). A noteworthy characteristic is that the primary and secondary ion optics are positioned so as to address the same side of the sample, i.e., the "reflection" mode; this allows the analysis of thin or thick samples without altering the geometry of the experiment. An added advantage of using a %2Cfsource is that ita predictable stable output is inherently most suitable for achieving precision in'analysis. Conversely, the low-intensity fission fragment output and their varying characteristics (energy, atomic number) preclude microprobe analysis or fundamental studies of the desorption phenomenon. In the subsequent sections we describe the experimental aspects of PDMS with a 252Cfsource and then for the case of minerals examine the performance of this method and compare PDMS with other analysis techniques.
2127
900 - H+ 750 -
600-
z 3
8 450300 -
I50
N+ , "K+
I I
-
cs+
03200 4000 4000 56bO t 00 CHANNELS Figure 1. PDMS positive bn spectrum of pollucite, Cs,AI,Si,016~H,0. Acquisition time was 3 h; sample bias was +9 kV. 800
1600 2400
3VK+
EXPERIMENTAL SECTION The design and operation of the apparatus used in this study are described elsewhere (15);however, a few pertinent details are given here. The drift length used in this series of analyses was 20 cm, which results in flight times on the order of 0 . 6 3 pa. The 25-pCi Cf source was positioned at 35O relative to the sample normal, and each fiision event was registered in a silicon surface barrier detector (Tennelec HI-100-60-30). Desorbed ions were detected in a chevron array of microchannel plates (Galileo FTD 2002) with 1000 V across each plate. Secondary ions were extracted by a potential field of +9 kV/mm in all cases, and all spectra were acquired for 3 h. Pressure during all analyses was 2 x 10" mbar. Digital flight times were generated by a multistop time digitizer capable of processing 255 stops per start with 0.5 ns resolution, made at the Institute of Nuclear Physics, Orsay, France (16,17). This module was hard-wired to a ND 66 MCA which was interfaced to a PDP 11/24 for data archiving. The acquisition time chosen for t h i series of experiments was chosen somewhat arbitrarily and can be readily reduced by 5 to 10 times by using a more intense californium source (Le., 50 pCi instead of 25 pCi) and by designing a more compact source-sample geometry. Geological specimens, consisting of pollucite (Bikita,Rhodesia), amblygonite and lepidolite (Keystone,SD), spodumene (Newry, ME), and microcline (CentralTexas),were purchased from Ward's Natural Science Establishment, Inc., Rochester, NY. Samples were prepared by National Petrographic Service, Inc., Houston, TX, as highly polished 1 mm thick disks, 1 cm in diameter. The polishing process consisted of sequential polishing of the mineral samples with 15 pm, 6 pm, and 0.25 pm diamond pastes with intermittent washing followed by a final polish with a 0.03-pm alumina slurry. Spodumene could not be successfully prepared and was deleted. Sample were mounted onto standard aluminum SEM mounts (Ted Pella, Inc., Tustin, CA) by silver conducting paint. SIMS anal- were performed on the Cameca IMS-3Fat Texas Instruments,Dallas, TX. Primary ion current was approximately 1 pA of 10-keV O', with an arc current of 58 mA and raster size of 500 pm. Secondary ion extraction voltage was +4500 V. Transfer optics were 150 pm with contrast aperture and field aperture of zero. The mass resolving power was set at 300. An electron flood gun was used in the positive ion analyses to compensate for charge buildup. EMP analysis was performed by use of a JEOL JSM-35CF with a Tracor Northern TN-2000 EDS system at the Texas A&M University Electron Microscopy Center. Samples were coated
2ootl;
0 0
, ;
Y;
c+ 800
N L AI+
,
1600 2400
,
?
,
3200 4 0 0 0
, 4000
;
j
5600 6400
CHANNELS Figure 2. PDMS positive ion spectrum of microcline, (K, Na)AISi,O,. Acquisition time was 3 h; sample bias was +9 kV.
with 100 A of carbon and the analysis area was 1 mm2 (1OOX integrated area analysis). Primary beam energy was 25 keV. XPS analyses were performed at the Surface Science Facility at Texas A&M University using the Kratoa XSAM-800. Primary excitation was provided by an Al anode biased at 12 kV using 20 mA filament current. Magnification was in the U l o ~position, " while resolution was in the "high" position.
RESULTS AND DISCUSSION Timeof-flight spectra for pollucite, microcline, amblygonite, and lepidolite are presented in Figures 1-4, respectively. All spectra were acquired for 3 h each under identical experimental conditions. The time calibration of the spectra is 0.5 ns per channel; thus the time scale of the spectra is about 3 ps. Common to all spectra are the low mass peaks, e.g., H+, Na+, and K+, which can be used to construct an empirical calibration curve of channel number w. the square root of the mass-to-charge ratio. Additionally there is a series in all spectra of low-intensity peaks at m/z ratios of 12, 13, 14, and 15, which corresponds to hydrocarbon Contaminants. Peaks present in low intensities in all spectra at m/z values of 43, 45, 51, 53, 55, 57, 61, 63, 65, 67, and 73 are attributable to impurities in the sample or contaminants from the vacuum system. The mass peaks register within a few channels (out of 8K channels) of those channel positions predicted on the
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 11, SEPTEMBER 1986
1
1500-
1250
0
'~i+
800
1600 2400 3200 4000 4800 5600 6400
CHANNELS
Figure 9. PDMS positive ion spectrum of amblygonite, LiAIFPO,. Acquisition time was 3 h; sample bias was +9 kV. 3500
I
I
I
I
I
I
I
C S+
3000
I
2500
2000
z 2
0
0 1500
1000
500
0 600
1600 2400 3200 4000 4800 5600 I
3
CHANNELS Figwe 4. PDMS positive bn spectrum of lepklollte, K&A13(AISi3010),. Acquisition time was 3 h; sample bias was +9 kV.
basis of analyses of alkali halide vapor deposits, which implies that there is no decrease in extraction field strength which would be indicated by a shift toward longer flight times. This is noteworthy given the insulating nature of the samples as well as the 1 mm thickness through which the potential field must be transmitted. Finally, the Occurrence of peaks such as Cs+ in the spectra of microcline, amblygonite, and lepidolite is not expected on the basis of the mineral formulas of these samples but can be attributed to the natural substitution of alkali metal atoms for each other in the mineral matrix. The presence of these "anomalous" alkali metals was confirmed by SIMS, XPS, and EMP analyses, the results of which are discussed below for the case of lepidolite. The time-of-flight spectrum of pollucite, a tectosilicate [Cs4Al4Si9OZ6-H20], is presented in Figure 1. In addition to the expected Cs+ peak, Na+, K+, Li+, and Rb+ peaks are also evident. Peaks at mlz ratios of 141 and 447 may be assigned to (Alz03)K+and (A1@3)4K+ (the absence of the dimer and trimer is perhaps attributable to lower stabilities of these species). Peaks corresponding to Mg+, Al+,Si+,and SiH+ are present in the region between Na+ and K+. This spectrum shows high flight time tails, which may be due to a slight decrease in the extraction field strength by the matrix itself or to a kinetic energy spread that is greater for this sample
than for the others. The secondary ion yield for this sample as a whole is also markedly lower than for the others. The time-of-flight spectrum for microcline, a tectosilicate [ (K, Na)A1Si308],is presented in Figure 2. The sodium and potassium peaks dominate the spectrum. Cesium is also evidenced, whereas lithium and rubidium are absent. Low-intensity peaks at mlz ratios of 27 and 29 are attributed to Al+ and SiH+. The peaks in this spectrum are notably sharper and more intense than those in Figure 1 although both matrices are silicates. Figure 3 shows the time-of-flight spectrum for amblygonite, a phosphate mineral [LiA1FPO4]. Amblygonite is approximately 10% LizO by weight (18)and the lithium isotopes at mlz values of 6 and 7 dominate the spectrum. Sodium and potassium are present as always, and a small cesium peak is again conspicuous. A small Al+ peak is present that is consistent with the empirical formula, while peaks at m / z values of 31 and 32 are attributed to Li+ (LiOH) and [Li2F]+,respectively. The peak a t m / z 37 is assigned to a lithium attachment molecule of LizO,e.g., Li' (LizO). The series at rnlz 77,93, and 109 progresses in increments of 16 daltons and is attributable to (Li,Na,J?Oz]+, where x ranges from 2 to 0 while y ranges from 0 to 2. Figure 4 is the time-of-flight spectrum of lepidolite, a phyllosilicate [K2Li3A13(A1Si3010)2], and is unique for the significant levels of all the alkali metal ions and the high secondary ion yield in general. Lepidolite is higher in LizO content than is amblygonite (10% vs. 3.3-7%) (18)and this trend is reflected in the spectra, although the matrices are dissimilar. The isotope pairs of rubidium, lithium, and potassium are all resolved, while the monoisotopic alkali metals, sodium and cesium, are also present in significant intensities. The sodium and cesium are present in such quantities as to form a series of attachment clusters (19) with chlorine and iodine which are also unexpectedly present in the mineral matrix. This series is of the form [Na,Cs,Cl]+, where x: ranges from 0 to 2 while y ranges from 2 to 0 (mlz values of 301,191, 81). The [Cs2C1]+molecule has been previously observed elsewhere (20). The iodine series is of the form [Na,Cs,I]+ where x ranges from 0 to 2 while y ranges from 2 to 0 ( m / z values of 393,283,173). Peaks at mlz values of 292,182, and 72 (masked by the mlz 73 contaminant peak) are attributable to the series (Na,Cs,CN]+, where x ranges from 0 to 2 while y ranges from 2 to 0. The high level of cesium, which was not expected given the empirical formula of lepidolite, as well as lower levels of cesium in microcline and amblygonite, was attributed at first to cesium contamination on either the extraction grid or sample surface. To clarify the origin of cesium, the samples were analyzed by SIMS, X P S , and EMP. Since the effect was most pronounced in lepidolite, only results from this sample are presented here. The presence of cesium was confirmed in the lepidolite sample by the observation of the 3d3/2, 3d5pcouplet at 740.1 eV and 726.1 eV, respectively, in the XPS spectrum. Further confinmation came upon the observation of peaks in the SIMS spectrum at mlz values of 133 and 66.5, corresponding to Cs+ and Cs2+,respectively. Those observations exclude a cesium contamination of the secondary ion extraction grid. To ensure that the cesium was not just a surface contaminant, the lepidolite sample was sputter cleaned for 5 min with 5-keV Ar+ and then reanalyzed by XPS. The cesium couplet remained unchanged in intensity, while the oxygen Is peak increased in intensity, indicating liberation of the matrix oxygen. Additionally, EMP analysis demonstrated that the cesium was localized rather than being uniformly distributed over the sample surface. These observations show that the Cs+ peaks in the desorption mass spectra are true indications of cesium
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Anal. Chem. 1986, 58, 2129-2137
occurrence not evidenced by the empirical formulas of the mineral samples. The results of this study demonstrate the feasibility of using ion induced desorption mass spectrometry for characterizing minerals. The method is nondestructive and is free from charging effects, which often complicate the use of charged particle beams for the surface analysis of insulating materials. It is also highly sensitive to the alkali metals and confirms the natural process of substitution of these ion species for each other in mineral matrices. The results presented are not quantitative, due in large part to the pronounced matrix effects that influence secondary ion yields. The desorption process is most efficient for elements with low ionization potentials. This is evidenced by the conspicuous absence of silicon and oxygen, which are present as major components of the sample matrix. ACKNOWLEDGMENT The experimental assistance of C. D. McAfee is hereby acknowledged. The XPS and EMP analyses were performed at the Texas A&M University Surface Science Facility. Beam time for the SIMS analyses was graciously provided by J. M. Anthony a t Texas Instruments Central Research Labs in Dallas, TX, where W.R.S. participated in a short-term collaboration. Registry No. nezCf,13981-17-4;pollucite, 1308-53-8;amblygonite, 1302-58-5; microline, 12251-43-3;lepidolite, 1317-64-2.
LITERATURE CITED (1) Moore, C.; Canepa, J. Anal. Chem. 1985, 57, 88R-94R. (2) Colby, J. W. I n PracHCal Scannlflg Hectron Microscopy; Goldstein, J. I., Yakoh, H., Eds.; Plenum Press: New York, 1975; pp 529-572. (3) Benninghoven, A. Trends Anal. Chem. 1984, 3(5), 112-115. (4) Turner, N.; Dunlap, B.; Colton, R. Anal. Chem. 1984, 56, 373R-416R. (5) Slodzlan, G. SIMS I I I ; Bennlnghoven. A., et al., Eds.; Springer-Verlag: Berlln, Heidelberg, New York, Tokyo, 1983; pp 115-123. (6) Conzemlus, R.; Slmons, D.; Shankai, 2.; Byrd, G. I n M/crobeam Analysls-1983; Gooley, R., Ed.; San Francisco Press: San FrancisCO,CA, 1983; pp 301-332. (7) Slmons, D. Inf. J . Mass Spectrom. Ion Processes 1984 55, 15. (6) Shaeffer, 0. A. ACS Symp. Ser. 1982, No. 776. 139-148. (9) Torgerson, D.; Skowronskl, R.; Macfarlane, R. Elochem. Eiophys Res. Commun. 1974, 60, 816-620. IO) Macfarlane, R. Acc. Chem. Res. 1982, 15, 266-275. 11) Macfarlane, R. Anal. Chem. 1983, 55, 1247A-1263A. 12) Fllpusluyckx, P. Ph.D. Dissertation, Texas ABM Unlverslty, College Station, TX, 1985. 13) Gunthler, W.; Becker, 0.; Della-Negra. S.; Knippelberg, W.; LeBeyec, Y.; W M , U.; Wien, K.; Wlesser, P.; Wurster, R. I n f . J . Mess Spectrom. Ion Processes 1983, 53, 185. (14) Macfarlane, R. D. J . Trace Microprobe Tech. 1985, 2(3,4), 267-291. (15) Summers, W. R.; Schwelkert, E. A. Rev. Sci. Insfrum. 1986, 57(4), 692-694. (16) Festa. E.; Sellem, R. Nucl. Instrum. Methods 1081, 188, 99-104. (17) Festa, E.; Sellem, R.; Tassan-Got, L. Nucl. Insfrum. Methods Phys. Res., Sect. A 1985, A234. 305-314. (18) Hurlburt, C. S. In Dana’s Menuelof Mlneralcgy, 18th ed.;Hurlburt, C. S., Ed.; Wlley Interscience: New York. 1971. (19) Ens, W.; Beavis, R.; Standing, K. G. Phys. Rev. Lett. 1983, 50(1), 27-29. (20) Castro, M. E.; Russell, D. H. Anal. Chem. 1885, 57, 2290-2293.
.
RECEIVED for review March 10,1986. Accepted May 12,1986. The authors gratefully acknowledge the financial support of the National Science Foundation under Grant CHE-8310783.
Multidimensional, Laser-Based Instrument for the Characterization of Environmental Samples for Polycyclic Aromatic Compounds R. L. M. Dobson, A. P.D’Silva, S.J. Weeks, and V. A. Fassel* Ames Laboratory-USDOE and Department of Chemistry, Iowa State University, Ames, Iowa 5001 1
A laser-based muitldlmenslonal analytical instrument that provides selective, senslllve, and on-line detection of polycyclk aromatk cOmpOunds (PAC) is described. The effluent of a capillary GC Is interrogated by a tunable UV laser beam at collision-free pressures. Selective excitatlon/lonizatlon occurs based primarily on the spectroscoplc absorption characteristics of the analyte molecules. The laser-analyte Interaction products (cations, electrons, and photons) are simultaneously monitored, permtttlng all of the analytically useful data to be extracted “on-the-fly”. The heart of this muitidlmensional detection scheme Is a time-of-flight mass spectnwneter that provkles access to an entire photoknizatkm mass spectrum for each laser pulse. This simultaneous measurement capability slmpllfles the task of PAC characterization, as is qualltatlvely demonstrated for a synthetic organic mixture and a Paraho shale oil fraction. Absolute detection limits In the low picogram range for 21 PAC and a linear dynamic range of 4 decades are reported.
Of the thousands of chemical compounds that have been deemed mutagenic or carcinogenic it is generally agreed that the polycyclic aromatic compounds (PAC) are among the most 0003-2700/86/0358-2129$01.50/0
potent (I). It is for this reason that a premium has been placed on the development of analytical methodology for the identification and quantitation of trace-level PAC in the environment. The many different sources, the variety of matrix compositions, and the overall complexity of most PAC-contaminated environmental samples impose several stringent requirements on methodologies for PAC determinations. Not only must the analytical approach allow detection of trace levels of both polar and nonpolar PAC in complex environmental matrices but also it must provide adequate selectivity so as to distinguish between various geometric and substitutional isomers (2, 3). Capillary column gas chromatography combined with mass spectrometry (CC/GC-MS) has become the most popular and effective analytical method for characterization of PAC in complex environmental samples (4-6). When employed in the conventional manner, the power of this technique is limited by the physical separation capabilities of the CC/GC, in that species that are well-resolved chromatographically are easily identified by the mass spectrometer. To minimize the impact of this limitation, environmental samples must usually undergo an extensive, time-consuming, cleanup and chemical class separation procedure prior to analysis by CC/GC-MS (6, 7). However, for the case of complex samples containing a number of coeluting isomers, it is impossible to provide full 0 1986 American Chemical Society
