Anal. Chem. 1986, 58,2189-2194 (2) Grifflths, P. R.; de Haseth, J. A.; Azarraga, L. V. Anal. Chem. 1983, 55, 1361A. (3) Bourne, S.; Reedy, 0.; Coffey, P.; Mattson, D. Am. Lab. (FaidieM Conn.) 1984, June. (4) Gurka, D. F.; Hiatt, M.; Titus, R. Anal. Chem. 1984, 56, 1102. (5) Brown, R. S.; Cooper, J. R.; Wllkins, C. L. Anal. Chem. 1985, 57, 2275. (6) Cooper. J. R.; Taylor, L. T. Anal. Chem. 1984, 5 6 , 1989. (7) Johnson, C. C.; Taylor, L. T. Anal. Chem. 1984, 56,2642. ( 8 ) Johnson, C. C.; Heilgeth, J. W.; Taylor, L. T. Anal. Chem. 1985, 57, 610. (9) Brown, R. S.; Taylor. L. T. Anal. Chem. 1981, 53, 197. (10) Brown, R. S.; Taylor, L. T. Anal. Chem. 1983, 55,723. (11) Sabo, M.; Gross, J.; Wang, J. S.; Rosenberg, I. E. Anal. Chem. 1985, 57, 1822. (12) Kuehl, D.; Griffiths, P. R. J . Chromtogr. Scl. 1979, 77,471. (13) Conroy, C. M.; Griffiths, P. R.; Jinno, K. Anal. Chem. 1985, 57,822. (14) Conroy, C. M.; GrlffHhs, P. R.; Duff, P. J.; Azarraga, L. V. Anal. Chem. 1984, 56,2636. (15) Kalasinsky, K. S.; Smith, J. A. S.; Kaiasinsky. V. F. Anal. Chem. 1985, 57, 1969.
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(16) Shafer, K. H.; Pentoney, S. L., Jr.; Grifflths, P. R. Anal. Chem. 1988, 58,58. (17) Jinno, K.; Fujimoto, C.; Hirata, Y. Appl. Spectrosc. 1982, 36, 67. (18) Fujimoto, C.; Jinno, K.; Hirata, Y. J . Chromtogr. 1983, 258, 81. (19) Henna, D. A.; Hangac, G.; Hohne, B. A.; Small, W. G.; Wleboldt, R. C.; Isenhour, T. L. J . Chromatogr. Sci. 1979, 77,423. (20) Karger, B. L.; Kirby, D. P.; Vouros, P.; Folk, R. L.; Hidy, E. Anal. Chem. 1979, 57,2324. (21) Castles, M. A.; Azarraga, L. V.; Carreira, L. A. Presented at the Pittsburgh Conference, Atlantic City, NJ, March 1984; paper 655. (22) Azarraga, L. V.; Castles, M. A.; Brackett, J. M.; Rogers, L. B. Presented at the Plttsburgh Conference, Atlantic City, NJ, March 1984; paper 656. (23) De Faubert Maunder, M. J. fractlcal Hints on Infrared Spectrometry; Adam Hllger: London, 1971; p 147.
RECEIVED for review February 18,1986. Accepted May 12, 1986. The work reported here was supported by Grants from the National Institutes of Health (ESO-1640 and ESO-2109).
Rapid Nontarget Screening of Environmental Extracts by Directly Linked Gas Chromatography/Fourier Transform Infrared/Mass Spectrometry Donald F. Gurka*
US.Environmental Protection Agency, Office of Research and Development, Environmental Monitoring Systems Laboratory, Las Vegas, Nevada 89114 Richard Titus
Chemistry Department, University of Nevada at Las Vegas, Las Vegas, Nevada 89109
A directly linked gas chromatography/Fourler transform infrared/mass spectrometry (GCIFT-IRIMS) system was constructed and evaluated for its capability to provlde rapld, on-line identlkatlon and compound class conflrmations. The validity of the forward on-line llbrary search results for each detector was evaluated with 50 organk standards. From the standard soiutlon experlence, forward search criteria were proposed for rapM GC/FT-IR/MS identlflcatlon and compound class screenlng. Six complex environmental extracts were analyzed with this system leading to 20 confirmed identlications and 24 confirmed compound class assignments. Since 106 anaiytes were jointly detected, this meant that 41 % of the joint detections resulted in confirmed structural informadetectors, each provided approximately tlon. As Ithe same amount of tentathe structural informatlon.
Currently the U.S.Environmental Protection Agency (EPA) screens the gas chromatographicable portion of sample extracts for a few hundred target organic compounds (1, 2). Since over 6 X lo4 manufactured chemicals are currently regulated under the Toxic Substance Control Act (TSCA) and thus may be found in the environment, and since the major portion of sample extract contaminants are not expected to be sufficiently volatile (3) to pass through a gas chromatograph (GC), this target compound approach clearly wastes most of the chemical information contained in such extracts. This is particularly disturbing since much of the total sample costs (in-the-field sampling, chain of custody, laboratory subaliquoting, and sample workup) have already been expended. The target compound approach is designed to minimize false 0003-2700/86/0358-2189$01.50/0
positives in regulatory situations and results in part from the general perception that there is a lack of sufficiently sensitive and selective detectors, other than mass spectrometers, for application to environmental organic analytical situations. The situation is further complicated by the necessity for confirmed environmental identifications (4-7),which has led to the current EPA GC retention time approach to confirming MS identifications. This confirmation approach presumes the availability of suitable pure organic standards and their GC resolution, a situation not always obtainable, especially for isomeric compounds. For example, the 22 isomeric tetrachlorodibenzodioxins cannot be resolved on a single GC column (8,9). In addition the utilization of GC retention time standards for confirmation would be extremely awkward and expensive for a target compound approach encompassing more than a few hundred compounds. The recent availability of hyphenated techniques (see ref 10 for a recent review) allows the construction of linked detector systems providing an increased amount of on-line chemical information. A directly linked gas chromatography/Fourier transform infrared/mass spectrometry (GC/ FT-IR/MS) system has been reported by several laboratories (11-13) and although one of these laboratories (11) has reported several multicomponent sample analyses, no environmental analyses have to date been reported for such a direct-linked system. However, Gurka et al. (14,15) and Shafer et al. (16)have reported the usefulness of independent GC/MS and GC/FT-IR analyses on hazardous waste extracts. These independent analyses suffer from an inexact correspondence between the FT-IR and MS reconstructed chromatogram peaks and possible analyte degradation before the confirmatory analysis. In addition a direct-linked system evaluation 0 1986 American Chemical Society
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is required prior to the preparation of suitable GC/E"I'-IR/MS computer software. The availability of a viable GC/FT-IR/MS system should greatly increase the chemical information obtained from environmental samples thereby allowing better risk assessment. This, in turn, should lead to more efficient cleanup and disposal measures a t the nation's uncontrolled chemical waste sites. In addition, on-line identification, chemical class, and quantitation confirmations will become available. The on-line identification confirmations would only be limited by the number of reference spectra that are common to both the MS and FT-IR search libraries. This number is currently estimated a t 1535 common entries for the 2300-member EPA library (17). Prior to the initiation of a GC/FT-IH/MS screening program, an attempt was made to assess previous GC/MS screening results which had been carried out on large numbers of environmental samples. Shackelford et al. reported the results of the U.S.EPA's survey of wastewaters by GC/MS spectrum matching. Approximately 30% of 225000 GC/MS detections in 4OOO samples led to 30% tentative identifications (18). Lucas et al. reported that 46% of 2383 GC/MS detections in 15 drinking water samples and 46% of 2097 detections in advanced treatment works (ATW) samples led to tentative identifications (19). Lucas' samples, however, received extensive pretreatment prior to GC/MS analysis. In a survey of wastewater GC/MS analyses Bursey et al. reported that use of other techniques, when GC/MS spectrum matching failed, did not usually lead to additional structural assignments (20). Bursey did point out that use of GC/FT-IR was extremely useful in some cases but that the FT-IR system employed was generally too insensitive. Since the system employed was an old packed column GC/FT-IR it may be supposed that this system was at least an order of magnitude less sensitive than modern capillary column GC/FT-IR systems (15). On the basis of these earlier studies, it appeared that GC/MS screening, in conjunction with GC/MS spectrum matching, would lead to no better than 30-50% tentative identifications. EXPERIMENTAL SECTION GC/FT-IR Instrumentation and Software. The FT-IR system consisted of a Digilab (Cambridge, MA) FTS-2OB spectrometer equipped with a medium-band, 1-mm2 focal chip mercury-cadmium-telluride detector (MCT). The data system included a Data General (Southboro, MA) Nova/4 computer, a 16-bit A/D converter, Digilab (Cambridge, MA) HI-COMP 32 high-speed array processor, and a Control Data Lark Model 50 megabyte disk system. With the Digilab GC/S software, four scans per second were collected to magnetic disk. The US.EPA 2300 vapor-phase FT-IR search library was used. Chromatography was performed with a Hewlett-Packard (Palo Alto, CA) Model 5880A with a J and W Scientific, Inc. (Rancho Cordova, CAI, l.@pmDB-5 film,fused silica capillary column (FSCC) GC column (30 m x 0.32 mm) at a flow rate of 1 mL/min of helium. The end of the FSCC column was interfaced to a nominal 101 effluent splitter which sent the major portion of the GC effluent to the FT-IRlightpipe and the lesser effluent stream to the mass spectral detector. The FT-IR transfer lines were maintained at 280 "C. The sensitivity and quality control requirements for the FT-IR system have been described elsewhere (21). A diagram of the GC/FT-IR/MS system is shown in Figure 1. After an initial hold time of 1 min, the GC oven was ramped from 40 to 280 "C at 10 OC/min and was held at 280 O C for 20 min. All GC injections were 2 pL and the FT-IR spectra were referenced against a 60-scan file of the chromatogram base line. GC/MS Instrumentation and Software. The mass spectrometer was a Hewlett-Packard 5970A mass selective detector (MSD) utilizing a 15-megabyte Winchester disk drive and a Hewlett-Packard 9816 desk top computer. The Hewlett-Packard Quicksilver Software and the 38 OOO NBS mass spectral library were used. The MSD was utilized in the full-scan mode (50-800
A
I C
H
Figure 1. GWFT-IR/MS interface: (A) MSD, (B) FT-IR interface, (C) oven, (D) on-column injector, (E) light pipe assembly, (F) Effluent vent, (G) splitter, (H) 30 m X 0.32 mm DB5 column, (I) 0.3 m X 0.23 mm DB5 coated line, (J) MSD interface.
GC
amu) collecting one scan/l.2 s at a nominal 1 amu resolution. Each day the spectrometer was calibrated with perfluorotributylamine. GC/MS and GC/FT-IR Structural Assignments. The appropriate library (38000 NBS or 2300 FT-IR spectra) was searched for the first five library hits. If these hits indicated close similarity indexes, additional hits were examined until significant mathematical differences appeared between sucessive library hits. Such hit differences have been shown to reveal the most valid search library selections for GC/MS and GC/FT-IR (14,15). It was assumed, a priori, that GC/MS could only determine the compound class of aromatic isomers and GC/FT-IR could only determine the compound class of homologous series members. All GC/MS and GC/FT-IR hits were hand checked except when the GC/MS similarityindex was below 7500 (best index = l O O 0 0 ) and the GC/FT-IR similarity index was greater than 0.90 (best index = 0.00) or when the GC/MS integrated area counts were less than 1OO00. If these three criteria were not met, the detection data received no further consideration. All FT-IRand MS analyte spectra that satisfied these criteria were hand checked against the library hit spectra. The GC/MS analyte molecular ion was compared to the molecular weight of each search kit. (Molecular ions were assigned by selecting the highest mass fragment which was at least 10% of the base peak intensity and which was also consistent with the FT-IRand MSD structural information.) The criterion for compound class aasignment was at least one functional group plus a differentiation between aromaticity or aliphaticity. The GC/MS search algorithm reduces each library and unknown mass spectrum to 10 peaks. The criterion for peak selection is mass times abundance. The mass spectral similarity index (SI) is defined as (22) loo0
x Am am
S I = looo
m=l
1oM)
( C (Am)*. (am)2)1'2 m=l
m=l
where Am is the abundance of the ion at mass m in the unknown spectrum and am is the abundance of the ion at mass m in the library spectrum. Environmental Extracts. Each of the sample extracts was received from EPA contractors and used as is. All samples were carefully dried methylene chloride extracts that did not receive extensive purification (the chlorinated hydrocarbon contaminated soil had been steam distilled). Standard Solutions. Solutions of organic compounds were purchased from Applied Sciences Corp. (State College, PA). The nine solutions contained C4-C, aliphatic alcohols, C9C13 1-alkenes, C12-Czzalkanes,C&, ketones, Cl-CI alkylbenzenes, methyl esters of clo-Cl8 acids, ethyl esters of c3-cB acids, propyl esters of CZ-cS acids, and butyl esters of C3-C7 acids. Twelve standard solutions containing four to six components each, were prepared containing about 300 ng/pL of each component. Each standard solution was injected separately into the GC/FT-IR/MS system to minimize chromatographic coelution.
ANALYTICAL CHEMISTRY, VOL. 58, NO. 11, SEPTEMBER 1986
2191
2.OE4. 0
5.0,
0
,
10 00
10.00
20.00
30.00
40.00
20.00
30.00
40.00
Minutes
Figure 2. Total Ion chromatogram (a) and Infrared reconstructed chromatogram (b) of herbicide still bottom extract.
RESULTS AND DISCUSSION Evaluation of the Directly Linked System for Rapid, Nontarget Screening, by Use of Standard Solutions. Standard solutions of alkanes, alkenes, alcohols, ketones, alkylbenzenes, and esters were used to evaluate the rapid screening capability of the directly linked system. A forward-search approach, using the first five MSD and FT-IR library search fits, was employed to determine to what extent spectral hand checking could be minimized. Spectral hand checking employs highly experienced spectroscopists and currently costs the EPA 50-80 dollars per hour. If the analyte’s spectrum is contained in both data bases, such hand checking under certain circumstances may be eliminated. If the analyte’s spectrum is not in either data base, the best one can expect is to determine the analyte’s compound class (functionality). The MSD and FT-IR on-line library search results for 50 standard compounds are summarized in Table I. Fifty-eight percent of the standards were identified by FT-IR and 18% by MSD, within the first five on-line library search hits. Seventy-two percent of the standards were contained within the FT-IR library while 98% were in the MSD library. In those cases where the standard was not in the FT-IR library, and the compound was not an alkene or an alkane, the FT-IR library search provided convincing proof of the molecular class by yielding a high percentage of search hits with the proper functionality. For compound class assignment (without hand checking) by the forward-search technique the FT-IR detector was superior for alcohols, ketones, ethyl esters, propyl esters, and butyl esters. The MSD detector was superior for alkanes and alkenes, and the two detedors were equally successful for alkylbenzenes and methyl esters. Fifty percent (52 of 103) of the correct MSD class hits were for the biologically inert class of alkanes and alkenes, while only 4% (7 of 179) of the correct FT-IR hits were for this class. MSD and FT-IR Structural Assignments. After evaluation of the interface with standard solutions, extracts of dye and manufacturing wastes and soils contaminated by organophosphorus pesticides and chlorinated hydrocarbons were analyzed by fused silica capillary column GC/F’T-IR/MS. These resulb are summarized in Table 11. FT-IR detections ranged from 15% to 137% of MSD detections but averaged about 33%. Figure 2 shows the real-time, simultaneously displayed, infrared reconstructed and total ion chromatograms of the herbicide still bottom. The herbicide still bottom was a chlorinated phenol waste residue and provided the greatest test for both detectors. In particular, the MSD detected 47 compounds of which the chromatogram peak intensity for most can be observed from Figure 2 to be well above the base line signal noise ( S / N ) . By use of the criteria outlined in the
0.134 3600
2000
2800
1600
700
Wavenumbers Flgure 3. FT-IR herbicide still bottom identifications: (a) tetrachlore ethylene, (b) 2,4dichlorophenol.
60
80
100 120 M/Z
140
1€
L
Figure 4. MSD stili bottom identifications: (a) tetrachloroethylene, (b) 2,4-dlchlorophenol.
Experimental Section, 23% of these MSD detections led to compound class information. FT-IR and MS retention times for corresponding chromatogram peaks generally agreed to within fO.O1 min. After an examination of the FT-IR and MSD library search fits and integration counts, those spectra exhibiting sufficiently high S I N , fits, and counts were visually examined for characteristic vapor-phase group frequencies (23,24)or fragment masses (25).The analyte mass spectral molecular weights are compared to those for analytes on the search-library lists. In addition the library search hits for both detectors were examined for chemical structural consistencies. It was found that the two detectors provided almost equal amounts of unique and common structural information. Figures 3 and 4 show the FT-IR and MS spectra of two peaks in the still bottom extract. Each detector identified these compounds as tetrachlorethylene and 2,4-dichlorophenol within the first five library hits. Thus, real-time identification confirmation was achieved without the extra data acquisition cost of standard GC retention time determinations. Figures 5 and 6 show the mass spectrum and FT-IR spectrum of a major
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NO. 11, SEPTEMBER 1986
Table I. FT-IR and MSD On-Line Search Results for Standards compound
library FT-IR MSD
search f i b b FT-IR MSD
identification* FT-IR MSD
+
2-methyl-1-propanol 1-butanol 2-ethyl-1-butanol 1-hexanol cyclohexanol 1-heptanol
0.20-0.24 0.16-0.20 0.18-0.23 0.13-0.20 0.16-0.28 0.13-0.18
8800-8400 9300-8800 8400-8300 9500-9100 9300-9200 9100-8800
1-decene 1-dodecene 1-undecene 1-tridecene 1-tetradecene
0.18-0.20 0.14-0.17 0.14-0.16 0.15-0.17 0.15-0.17
9300-9100 9300-9200 9400-9300 9300-9250 9400-9100
n-dodecane n-tridecane n-tetradecane n-hexadecane n-octadecane n-nonadecane n-heneicosane n-docosane
0.09-0.13 0.09-0.13 0.10-0.13 0.13-0.15 0.49-0.50 0.23-0.24 0.21-0.23 0.26-0.28
9100-8900 9000-8900 9000-8800 9100-9000 9200-9000 9200-9000 9300-9000 9300-9000
0.32-0.42 0.19-0.28 0.21-0.26 0.23-0.27 0.22-0.28 0.25-0.28 0.20-0.31
9200-9100 8100-7700 9200-9100 9600-9300 9700-9400 8300-8100 9300-9000
0.17-0.76 0.17-0.49 0.15-0.46 0.17-0.57 0.12-0.52 0.17-0.35
8800-8600 9800-9700 9800-9600 9900-9500 9700-9600 9800-9400
+ + + + + + + + + +
0.19-0.26 0.59-0.60 0.22-0.24 0.22-0.24 0.18-0.20
9200-9000 9600-9500 9600-9400 9600-9400 9600-9400
+ + +
-
0.32-0.38 0.18-0.33 0.22-0.29 0.17-0.26
9400-9300 7800-6800 6800-6600 8600-8400
+ +
-
0.21-0.29 0.18-0.24 0.22-0.31 0.21-0.31 0.19-0.28
8000-6300 8600-7800 8300-8100 8100-7700 7600-6100
+ +
0.18-0.23 0.17-0.27 0.19-0.26 0.19-0.25
9400-9300 7000-6700 9200-9000 8300-7500
3-pentanone 4-methyl-2-pentanone 5-methyl-2-hexanone 4-heptanone 2-heptanone 5-methyl-3-heptanone 2,6-dimethyl-4-heptanone
-
benzene to1uen e ethylbenzene rn-xylene 0-xylene p-cymene methyl methyl methyl methyl methyl
decanoate dodecanoate tetradecanoate hexadecanoate octadecanoate
ethyl propionate ethyl butyrate ethyl valerate ethyl caproate propyl propyl propyl propyl propyl butyl butyl butyl butyl total
acetate propionate butyrate valerate caproate
propionate valerate caproate heptanoate
-
-
-
-
14d
2d
+ + + + + + + +
+
+
+ + + + +
+ +
+
+ + 29
9
class hitsC FT-IR MSD 5 5 5 5 5 5
1 0 0 0 1 0
2 1 1 2 0
4 2 2 3 1
0 0 0 0 0 0 0 1
5 5 5 5 5 5 5 5
5 5 5 5 5 5
0 1 0 0 0 0
4 3 3 4 3 5
0 1 4 4 4 5
5 5 5 5 5
4 4 4 4
5
5 5 5 5
0 2 0
5 5 5 5 5
0 1 0 1 1
5 5 5 5
0 1 2 0
179 (250)e
1
103 (250)‘
“ A =-” indicates that the standard is not in the search library. *First five library search hits. ‘Number of library search hits, within the first five hits, with the proper functionality. dNumber of standards missing from library. eMaximum number of hits.
peak in the pesticide soil extract. Both the FT-IR and MSD searches identified this peak as an organosulfur-phosphorus compound. The FT-IR vma. was at 1038 cm-’ and the spectrum was very similar to that of Diazinon, a phmphorothionate (26). The mass spectrum contained fragments at m / z 88 (base peak) and m / z 60. These ions correspond to [CH2= CHSC2H5]+and [CH2=CHSH]+respectively, also suggesting a phosphorothionate (27). This was an example of an on-line compound class confirmation. Since essentially all FT-IR detected analytes were also detected by the MSD, approximately 41% of the jointly
detected analytes [(20+ 24)/106]led to structural confirmations. This is surprisingly high in light of the general perception that GC/FT-IR is insensitive and that the FT-IR vapor-phase library is too small. Implementation of the GC/F’T-IR single-beam sensitivity improvements of Griffiths et al. (28, 29) will dramatically improve the capability of GC/FT-IR/MS by bringing the number of FT-IR detections more in line with that obtainable from the MS detector. Sample Representativeness. While these samples exhibit a variety of matrix types, it is also important to ascertain that a broad spectrum of analyte types were present. The com-
ANALYTICAL CHEMISTRY, VOL. 58, NO. 11, SEPTEMBER 1986
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Table 11. Comparison of FT-IR, MSD, and FT-IR/MSD Selectivities
sample dye 1 dye 2 dye 3 herbicide still bottom pesticide soil chlorohydrocarbon soil total
no. detected FT-IR MSD
meet" criteria FT-IR MSD
4 4 7 56 34
3 6 7 47 41 121
1 1 4 7 51 33
1 4 7 28 32 78
106
225
97
150
1
compound class (tentative) FT-IR MSD
(tentative) FT-IR MSD
1 1 1 4 24 10
1 2 11 13 31b
0 0 1 2 5 17
1 1 1 3 3 10
0 0 0 2 3 15
1 1 2 3 10 7
41 (27)'
59 (32)d
25 (13)'
19 (9)d
20
24
1
no. identified
FT-IR/MSD confirmation ident class
a Meet the three criteria of the Experimental Section (GC/MS and GC/FT-IR structural assignments). *Sample contained many aromatic isomers. MSD used alone can only determine compound class. Unique FT-IR information. Unique MSD information.
Table 111. FT-IR and MSD Tentative Structural Assignments class
no. 1
dyes no. 2
no. 3
still bottom
chlorohydrocarbon soil
pesticide soil
acid alcohol aldehyde alkane alkene amide amine aromatic hydrocarbon chlorohydrocarbon ester ether fluorohydrocarbons ketone nitro organophosphorus phenol
total 2 7 2 18 2 6 3 17 17 9 4 4 2 4 7 2
total
106
"Total uniaue FT-IRand uniaue MSD assignments. bFT-IRresult, MSD result.
2.51
1do
260 M/Z
360
Figure 5. MSD pesticide soil compound class assignment: (a) analyte, (b) substituted phosphorodithioic acid, (c) substituted phosphorothionate, (d) substituted phosphorothionate.
pound types found by each detector in each sample extract are summarized in Table 111. A total of 106 tentative class assignments representing 16 compound classes were made by the directly linked system. The dominant class types were alkanes, aromatic hydrocarbons, chlorinated hydrocarbons, and organophosphorus compounds. As was the case with standards, a high percentage of the MSD class assignments were of the biologically inert class of alkanes and alkenes (20179 = 0.25). For the 45 oxygen-containing compounds, FT-IR was able to make tentative class assignments on 28 while the MSD provide tentative class information on 30. The MSD provided tentative class information on 25 of 34 aromatic and chlorinated hydrocarbons, while the FT-IR provided 32 assignments. The importance of proper identification of
3200
2925
2367
isio
1255
700
Wavenumber Figure 8. FT-IR pesticide soil compound class assignment. Substituted phosphorothionate.
oxygen compounds is to be emphasized since such compounds are polar and the polar fraction of sample extracts has been reported to be mutagenic (30). The mass spectral selectivity for the environmentally ubiquitous chlorine-containing compounds is greatly aided by the unique chlorine isotopic clusters (see page 19 of ref 25 and page 59 of ref 27). It should also be pointed out that although the nominal MS search library size is over 38 000 spectra, most of these are not the spectra of compounds likely to be found in the environment. Milne et al. (31) have pointed out that less than 6000 of the spectra
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 11, SEPTEMBER
in the NBS data base are those of manufactured chemicals registered under TSCA. In addition, the MS reference spectra have been measured by direct probe insertion; thus many of the library reference chemicals may not actually pass through a GC transfer line, in sufficient quantity, to be detected (note that this also may apply to some of the 6000 TSCA chemical mass spectra). For a complete survey of mass spectral data bases, see ref 32. By contrast, most or all of the 2300 FT-IR spectra are those of common manufactured chemicals, werc measured in the gas-phase, and were selected because they had been previously observed in the environment (33). In addition, Frankel has shown (34)that this FT-IR library of 2300 spectra contains all the compound types required to develop a pattern recognition identification algorithm for organic compounds.
CONCLUSIONS I t is understood that more exhaustive spectral hand checking or sample cleanup would improve the performance of this system, but not without a substantial increase in analytical costs. In addition, more sophisticated computer software of the type described by McLafferty (35) would greatly improve the MSD capability, which is currently limited by a small desk top computer. An order of magnitude improvement in FT-IR sensitivity will greatly improve GC/FT-IR/MS for high throughput, nontarget screening of complex environmental, multicomponent samples. Not only will this bring the number of FT-IR detections more in line with those obtained from MS but it will also allow the use of narrow bore capillary columns in the directly linked system, thereby reducing chromatographic coelution. Directly linked GC/FT-IR/MS is demonstrated to be superior to either stand-alone technique for environmental analyses. This superiority can be routinely implemented when suitable computer software becomes available to process the large quantities of spectral information tha . will be generated. Wilkins has reported a preliminary version of such software (36). The computer software and the F"-IR sensitivity improvements are being pursued via a grant from this laboratory to the University of California at Riverside (37). In his elegant review of hyphenated techniques ( I O ) , Hirschfeld noted that the extravagance of such techniques may only be justified by sufficiently high sample demands. Such high sample demands currently exist within the EPA'E Superfund Laboratory Contracts Program within which over 20 000 organic samples (this excludes 7000 dioxin samples) were processed inf984 (38). The availability of small, relatively inexpensive, mass spectral detectors such as the MSD and the ion trap (39),as well as small FT-IR detectors (40) suggests that this "extravagance" may not be as great as formerly anticipated. ACKNOWLEDGMENT The authors wish to thank Charles Wilkins of the University of California a t Riverside for several helpful discussions. Registry No. Phenol, 108-95-2;tetrachloroethylene, 127-18-4; 2,4-dichlorophenol, 120-83-2. LITERATURE CITED (1) Gurka, D. F.; Meier, E. P.; Beckert, W. F.; Haeberer, A. F. Paper pres-
ented at the 3rd National Conference on Management of Uncontrolled Hazardous Waste Sites. Washington, DC, November 1982. (2) Fed. Regist. 1979, 44(233), 69464-69558.
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RECEIVEDfor review July 23, 1985. Resubmitted April 21, 1986. Accepted May 12, 1986. Although the research described in this article has been funded wholly or in part by the United States Environmental Protection Agency, it has not been subjected to Agency review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. This work was presented in part at the 24th Eastern Analytical Symposium, November 21, 1985, New York, NY.
