Environmental Applications
Donald F. Gurka, L. Donnelly Betowski, Thomas A. Hinners, and Edward M. Heithmar U.S. Environmental Protection Agency Office of Research and Development Las Vegas, Nev. 8 9 1 9 3 - 3 4 7 8
Richard Titus Chemistry Department University of Nevada at Las Vegas Las Vegas, Nev. 8 9 1 5 4
John M. Henshaw Lockheed-EMSCo Las Vegas, Nev. 89919
Quadrupole mass spectrometers cur rently enjoy widespread analytical us age that has been estimated a t more than 80% of the total mass spectrome ter market (1 ). T h e availability of com p u t e r - s u p p o r t e d q u a d r u p o l e mass spectrometry (QMS), its high intrinsic sensitivity, and its compatibility with gas chromatographs led to its adoption
T h e complexity of environmental samples (as many as 50-100 organic components, at widely varying concen trations, in diverse sample matrices), t h e intrinsic shortcomings of Q M S when used alone, and the regulatory significance of environmental analyti cal results have led to a cautious targetlist approach to organic environmental analysis (2). This approach requires target-list-type validated protocols, reference spectra, and authentic stan dards. Although the current number of standards in the E P A standards repos itory is about 1500, and the C I S - N I H E P A mass spectral database contains about 44,205 reference spectra, t h e number of known chemicals is now about 9 Χ 10 6 and is reported t o be increasing a t a rate faster than expo nential (see Figure 1). T h e situation is not quite as complex in elemental analysis, b u t the heavy analysis loads inherent to routine mon-
INSTRUMENTATION in the late 1970s by the U.S. Environ mental Protection Agency (EPA) as its primary monitoring tool for trace organics. In contrast, t h e predominant methods for elemental environmental analysis thus far have been flame or graphite furnace atomic absorption spectrometry (GF-AAS) a n d induc tively coupled plasma atomic emission spectrometry (ICP-AES).
itoring and t h e very high sensitivity usually required cannot be simulta neously accommodated by either of the two commonly used methods. Addi tionally, the complex nature of envi ronmental samples often leads to con siderable problems with spectral inter ferences in ICP-AES and to chemical or physical interferences in flame AAS or GF-AAS.
454 A · ANALYTICAL CHEMISTRY, VOL. 6 0 , NO. 7, APRIL 1 , 1988
8,000,000 6,000,000 4,000,000 2,000,000
1900
1950
7.0
6.8
2000
11 yrs. Doubling time 14 yrs.
6.6 24 yrs.
6.4 43 yrs. 6.2 1940
1960
1980
Year
F i g u r e 1 . R a t e of i n c r e a s e in k n o w n chemicals. (Adapted with permission from Opportunities in Chemistry, © 1985 by the National Academy of Sciences.)
0003-2700/88/0360-454A/$01.50/0 © 1988 A m e r i c a n Chemical Society
of Hyphenated Quadrupole Techniques
Clearly, new approaches to environmental monitoring are required t h a t can maximize the a m o u n t of sample information obtained in a cost-effective fashion. These new approaches should more efficiently separate cont a m i n a n t analytes from interferences and should provide more analyte information. Powerful computer software is required to collect, refine, and interpret the additional analytical data. Hyphenated techniques can provide an expanded analytical capability through the linkage of two or more spectral or separation systems t h a t possess synergistic properties (3). In this article we discuss applications of three systems having great potential for improved environmental analysis. These are directly linked gas chromatography/Fourier transform infrared/ mass spectrometry ( G C / F T - I R / M S ) , thermospray/triple quadrupole mass spectrometry (TQMS), and inductively coupled plasma/mass spectrometry (ICP/MS). Some aspects of these hyphenated systems have been reviewed elsewhere (4-6). T h e flow s c h e m e shown in Figure 2 outlines the sequencing of sample introduction, analyte ionization, and data collection for these three (and related) hyphenated techniques. Directly linked F T - I R / M S systems
A directly linked F T - I R / M S system has important advantages such as the following for environmental semi- or nonvolatiles analysis. F T - I R and QMS spectral data can be collected simulta-
Examples, comments No
Analyte^ (ion) separation required?. Yes Analyte (ion) separation
Neutral analyte
Single or multicomponent?
Chromatographic or mass separation
Analyte (ion) introduction Yes Yes:GC/MS
Non-MS spectral technique
No
Ionization required?
Ionization mechanism Computer interpretation
No: Thermospray, plasma, electrospray, particle desorption
Yes: Thermospray No
Need more fragmentation'? Yes Collisional dissociation quadrupole
No: Electron impact GC/MS Triple quadrupole mass spectrometry (TQMS)
Quadrupole analyzer
Figure 2. Hyphenated quadrupole analyte separation, introduction, ionization, and detection scheme. ANALYTICAL CHEMISTRY, VOL. 60, NO. 7, APRIL 1, 1988 · 455 A
Figure 3. On-line compound class confirmation of 2,4,5-T waste semivolatile by (a) FT-IR and (b) quadrupole detectors. (Adapted from Gurka, D. F.; Betowski, L D.; Jones, T. L; Pyle, S. M. J. Chromatogr. Sci. 1988, 26, in press, by permission of Preston Publications, A Division of Preston Industries, Inc.)
neously, thereby providing complementary spectral data. QMS can provide molecular weights, halogen isotopic clusters, and other characteristic substructural information. FT-IR can distinguish isomers, provide group frequency data, and absorption coefficients for quantitation. In addition, the system can minimize dependence on certified standards by using FT-IR to confirm QMS identifications, using FT-IR to decrease the uncertainties associated with QMS tuning problems (QMS used alone requires standards for user-created spectral libraries to ensure analyte and reference spectral comparability), and using FT-IR absorption coefficients to eliminate the need for quantitation standards. Absorption coefficients obtained from FT-IR should exhibit instrument-toinstrument reproducibility greater
Table I.
than that obtained from grating IR instruments, but this capability has yet to be demonstrated. The commercial availability of gas chromatographic interfaces for FT-IR and QMS systems resulted in early reports of their successful linkage (7, 8). These reports were soon followed by the first published environmental applications of directly linked GC/FTIR/MS systems using both a quadrupole mass spectrometer (9) and an ion trap (10). Particularly striking was the finding that 42% of the jointly detected analytes in environmental samples were confirmed by identity or compound class (see Table I). Compound class confirmations are useful because they are not dependent on the availability of large search libraries and because class information may be sufficient to assess biological hazard (11).
The complexity of environmental samples, coupled with the inaccessibility of certified standards, ensures that compound class confirmation generally will be the best result obtainable in the environmental nontarget compound approach. Figure 3 shows a striking example of the capability of a directly linked GC/ FT-IR/MS system for assessing analyte toxicity without the determination of analyte identity. The analyte was a constituent of a 2,4,5-T manufacturing waste. The data from the quadrupole mass spectrometer indicated a 4-chlorine isotopic cluster and five sites of unsaturation. FT-IR indicated two adjacent and one isolated benzene hydrogen in an aryl ether. This indicated one aryl chlorine and three chlorines in a fused-ring cyclic ether. Thus both the alpha and beta ether positions cannot
Comparison of FT-IR, MSDa, and FT-IR/MSD selectivities
Environmental sample Dye waste no. 1 Dye waste no. 2 Dye waste no. 3 Herbicide still bottom Pesticide soil Chlorohydrocarbon soil Total
r
No. detected T-IR MSD
Mee>t criteria 6 FT-IR MSD
Compound class (tentative) FT-IR MSD
No. iden tified (tentât ve) FT-IR MSD
FT-IR/ MSD confirm ation Identity Class
1 4 4 7
3 6 7 47
1 1 4 7
1 4 7 28
1 1 1 4
1 1 2 11
0 0 1 2
1 1 1 3
0 0 0 2
1 1 2 3
56 34
41 121
51 33
32 78
24 10
13 31c
5 17
3 10
3 15
10 7
106
225
97
150
41 (27) d
59 (32) e
25(13) d
19 (9) e
20
24
Source: Reference 9. " MSD = mass selective detector. 6 Meet the reporting criteria for GC/MS and GC/FT-IR structure assignments cited in Reference 9. c Sample contained many aromatic isomers. MSD used alone can only determine compound class. "Unique FT-IR information. 8 Unique MSD information. Number of identifications increased to 18 when the probability-based matching (PBM) algorithm was used in place of the previous system software.
456 A · ANALYTICAL CHEMISTRY, VOL. 60, NO. 7, APRIL 1, 1988
contain inert substituents of the gemdichloro type. The unknown must then represent a powerfully electrophilic alpha or beta chloro ether that can be mutagenic via biomolecule alkylation (12). Although directly linked GC/FT-IR/ MS systems are now commercially available, progress on the development of such systems for environmental nonvolatiles has been slow. These nonvolatiles comprise the greater portion of environmental sample extractables, and the nonvolatile fraction of water or other environmental sample types is often mutagenic to the Ames test (13). Currently, progress in achieving standalone QMS systems for multicomponent nonvolatiles analysis is much further along than that for stand-alone FT-IR. The availability of FT-IR instrumentation capable of nonvolatiles analysis is being delayed until solutions are obtained to the problems of continuous flow versus solvent elimination/ FT-IR and of high-performance liquid chromatography (HPLC) versus supercritical fluid chromatography (SCF) FT-IR (14). The recent disclosure of a potentially universal FT-IR chromatographic interface (GC, HPLC, SCF) may provide a permanent resolution to one of these difficulties (15). This universality is dependent on the need of many chromatographic interfaces for mobile-phase removal. For maximum application to environmental analysis, such an interface should be compatible with high-water-content, reversedphase HPLC solvents. However, confirmatory nonvolatiles analysis may still be carried out by offline diffuse reflectance FT-IR (DRIFT) and thermospray/TQMS or fast atom bombardment (FAB) QMS. Diffuse reflectance is a surface sampling technique that uses a film of analyte deposited on an IR-transparent solid substrate (pure solid analytes may be directly mixed with the sub-
Table II. Environmental applications of thermospray and nonthermospray TQMS Application type Carbamate pesticides Organophosphorus pesticides Dye-containing effluents Manufacturing wastes Oil shale gas mixtures containing sulfur compounds Air analysis Priority pollutants
Category
Reference
Thermally labile Selected reaction monitoring Nonvolatiles Nonvolatiles Eliminate chromatography
35 36
Eliminate chromatography Eliminate chromatography, minimize sample cleanup
strate). Thus HPLC fractions may be deposited directly on the substrate, the solvent removed, and the analyte-film substrate scanned by FT-IR. Although the HPLC fractions are not analyzed on line, total DRIFT sample preparation and analysis time is typically less than 5 min per component. Figure 4 shows the DRIFT and confirmatory GC/MS spectra of a 2,4,5-T waste nonvolatile, which was not amenable to conventional GC until derivatized, but was directly amenable to DRIFT as the acid salt. Thermospray/TQMS
This hyphenated technique is unique in that separated ions rather than separated analytes may be presented to an analyzer quadrupole; the presence of a third quadrupole allows the generation of daughter ion profiles by collisionally activated dissociation (CAD). These profiles are used in conjunction with the pseudomolecular ions generated by the "soft" thermospray approach, in
20 19 37
18 17
which they are mass-separated in the first quadrupole. If an HPLC is used to provide multicomponent separation for the thermospray/TQMS, on-line environmental nonvolatiles and semivolatiles capability with a single analysis can be achieved. Table II lists examples of distinct types of TQMS environmental applications. First, the mild chromatographic separation conditions of thermospray are amenable to thermally labile carbamate and organophosphorus pesticides; second, the thermospray/TQMS approach can be used to characterize toxic environmental nonvolatiles; third, one of the TQMS quadrupoles can be used to minimize sample cleanup and eliminate chromatographic separation; and fourth, the first quadrupole can be used to select parent ions that are then subjected to CAD fragmentation in quadrupole 2 (reaction monitoring). Obviously the third item could result in a significant decrease in analytical cost. Much of the early TQMS work cen-
Figure 4. Identification confirmation of 2,4,5-T manufacturing waste (a) nonvolatile by DRIFT and (b) derivatized nonvolatile by QMS. 458 A · ANALYTICAL CHEMISTRY, VOL. 60, NO. 7, APRIL 1, 1988
components is shown in the positive ion thermospray/TQMS spectrum of commercial Basic Red 14 (see Figure 5). Because thermospray is a "soft" ionization technique, the peaks at m/z 174, 189, 291, and 344 were attributed to protonated molecules or molecular ions of the dye mixture (see box). Each of these ions was selected in quadrupole 1 and subjected to CAD in quadrupole 2. The CAD-induced fragmentation patterns allowed the assignment of structures 1-4 to these ions, and m/z 174,189, and 291 were attributed to the protonated molecules or molecular ions of Basic Red 14 (m/z 344) dye precursors. Another quadrupole technique with great potential for environmental nonvolatiles analysis is the monodisperse aerosol generator for introduction of liquid chromatographic effluents (MAGIC). This approach converts an HPLC effluent to a physically homogeneous aerosol (21), but it has yet to be evaluated for environmental analysis. Inductively coupled plasma/mass spectrometry
tered on demonstrating that this technique could shorten analysis time by minimizing sample cleanup and chromatography (16,17) rather than on emphasizing the higher information content derived from a system possessing both CAD and analyzer quadrupoles. Although there is some empirical evidence that analysis time is shortened, TQMS real sample data collected over a long period of time are required to demonstrate that system downtime does not negate the cleanup-chromatography time savings. An approach that should not "dirty" the TQMS, and thus not lead to downtime, is the direct analysis of gaseous mixtures. A project is underway within the EPA to directly analyze gaseous mixtures in the field by employing a mobile-van-based TQMS (18). Perhaps the most exhaustive environmental study thus far that uses thermospray/TQMS has concerned the characterization of dyes. Dye wastes, degradation products, and dye intermediates form a class of highly carcinogenic compounds that currently are being discharged into the environment. These compounds present a difficult analytical problem, because they are intractable mixtures of thermally sensitive and photosensitive nonvolatile compounds. Ballard and Betowski have demonstrated the applicability of thermospray/TQMS to the characterization of azo, methine, anthraquinone, coumarin, triarylmethane, and xanthene dyes (19, 20). Detection limits of
2-200 ng and precision comparable to that obtained from HPLC with ultraviolet detection have been demonstrated. Thermospray/TQMS is believed to be the current method of choice (and perhaps the only viable method) for the routine monitoring of dye-manufacture and dye-use effluents. An example of the power of CAD to identify unknown nonvolatile mixture
Commercial instruments that use an inductively coupled plasma as an ion source for QMS became available in 1983. ICP/MS combines a sensitivity approaching that of GF-AAS with the throughput capabilities of multicomponent ICP-AES. This has prompted a number of investigations into the applicability of ICP/MS to environmental samples. McLaren determined seven elements in seawater following preconcentration by ion exchange (22). The preconcentration step was necessary because the natural levels of some
mlz Figure 5. Thermospray/TQMS positive ion spectrum of the nonvolatile mixture, Basic Red 14. (Adapted from Anal. Chem. 1984, 56, 2604-07.)
ANALYTICAL CHEMISTRY, VOL. 60, NO. 7, APRIL 1, 1988 · 461 A
Figure 6. Frequency of detection by ICP/MS for 45 elements in lakes in the eastern United States. Analyses were performed in a rapid multielemental mode. System detection limits were generally less than 0.2 ppb.
of the metals in seawater are below the detection limits of ICP/MS. Ion exchange also allowed the separation of the trace elements from the high salt matrix, which would have caused severe suppression effects. Garbarino used isotopic dilution to determine trace metals in natural waters (23), and McLaren used the same technique for the analysis of marine sediments (24). The applicability of the isotopic dilution technique is an advantage of ICP/MS in environmental analyses because recoveries are often low. The method of standard additions (MSA) must be employed in most analyses by GF-AAS. Isotopic dilution is inherently more precise than MSA because the concentration is obtained in a single analysis. Isotopic dilution also requires about one-third the analysis time of MSA. The results of earlier studies of the application of ICP/MS to environmental samples encouraged EPA to incorporate the method into the Eastern Lakes Survey (ELS) of the Aquatic Effects Research Program. The intent was to demonstrate and use the capabilities of this new technology in a large-scale environmental survey with rigorous quality-assurance criteria (25). The ICP/MS analyses will provide additional insight into the effects of acidic deposition in aquatic systems by supplementing data obtained by conventional methods. A total of 267 samples from 118 lakes in the eastern United States were analyzed by ICP/ MS. Calibration standards were used for 22 elements, some of which acted as models for the response of approximately 30 more analytes. ICP/MS allows the confident use of such surro-
gate elements because of its similar sensitivity for elements of like mass and ionization energy. Figure 6 shows the percentages of the sampled lakes that had detectable concentrations for the indicated analytes. It is obvious that lake waters, like seawater, pose a challenge to the sensitivity of even ICP/MS. The survey data currently are being evaluated to determine relationships among trace-element concentrations and between trace elements and other parameters (e.g., pH, alkalinity, sulfate, watershed characteristics, etc.). These interactions are quite complex, and multivariate statistical approaches are being applied to the data. Figure 7 illustrates some simple trends that are
often observed within subsets of similar lakes. The mean concentrations of trace elements are shown for two groups of lakes from the same geographical region and general classification. All else being equal, higher concentrations of aluminum, first-row transition elements, rare earth elements, and lead are associated with lower pH values. In addition to its multielemental capability, ICP/MS can be used to determine elemental isotopic ratios. As early as 1974, Doe and Stacey of the U.S. Geological Survey had postulated that lead isotopic ratios were characteristic of specific ore deposits (26). This suggested that isotopic ratios may be used to track some environmental contaminants to their source, resulting in regulatory or remedial action. Hinners et al. have measured the m/z 208/206, 207/ 206, and 204/206 isotopic ratios by ICP/MS for lead ores mined in Idaho, Missouri, and Yugoslavia, as well as for other lead standards (27). Isotopic ore ratios for these areas differed by as much as 19%. If these isotopic ratio differences are typically outside the experimental error, this approach to pollutant tracking has a bright future. Previously, Rahn and Lowenthal reported that elemental tracers can be used to pinpoint the regional sources of atmospheric aerosol pollution (28). The extra selectivity associated with elemental isotopic ratios, and the high sample throughputs required to validate such a tracer technique, may be achieved with ICP/MS. Future instrumentation needs Commercially available hyphenated quadrupole techniques are providing new and efficient solutions to the problems of complex environmental sample analysis. Nevertheless, additional sup-
Figure 7. Typical relationships observed between lake pH and trace elemental concentrations measured by ICP/MS. Other factors such as geographic location are held constant. Each concentration is the mean of 5 lakes. * = concentration X 10; * * = concentration X 100; * * * = concentration X 1000.
462 A · ANALYTICAL CHEMISTRY, VOL. 60, NO. 7, APRIL 1, 1988
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Table III. Commercial interfaces required for future hyphenated quadrupole applications Interface type
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Environmental application Multicomponent nonvolatiles and thermally labiles analysis Multicomponent semivolatiles and nonvolatiles analysis Confirmed multicomponent nonvolatiles and thermally labiles analysis Speciation analysis, isotopic dilution, analysis of complex samples Multicomponent low-proton-affinity nonvolatiles analysis
Reference 14
31-33 14
38,39
40
* When this manuscript was written a flow SCF/FT-IR commercial system was introduced (Chem. Eng. News, 1987, 54).
port is required from the private sector, as indicated by the needs cited in Table III. Viable on-line multicomponent, nonvolatlles capability is not available for stand-alone FT-IR, much less for linked FT-IR/MS. Flow-cell FT-IR systems have been available for years, but their insensitivity, coupled with the "solvent window" problem, has greatly limited their use. Techniques to provide electron-ionization-type nonvolatlles fragmenta tion (29), which are less expensive than TQMS collisionally activated dissocia tion, are needed to complement the soft thermospray approach (however, TQMS system prices have recently de clined [30]). Preliminary claims indi cate that the MAGIC technique may satisfy this need (21). In addition, quadrupole interfaces with multicom ponent capability, which are also ame nable to low-proton-affinity nonvola tlles, are required to support thermospray/TQMS. Wider mass range quad rupole mass spectrometers are needed to meet the demands of high-molecu lar-weight, nonvolatile environmental contaminants. In the area of inorganic analysis, there is increasing awareness that trace-metal speciation information is often more environmentally significant than total metal concentration. Thus interfacing ICP/MS with HPLC and ion chromatographs will be necessary in the future. Flow-injection sampling systems or robotics would make the isotopic dilution technique more viable for routine analysis. "Intelligent" data
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acquisition and analysis software, com bined with automated sampling and in strument control systems, could great ly increase ICP/MS throughput by automatically ordering sample dilu tions, plasma parameter changes, or other manipulations, depending on the results obtained in an initial scan. This would not only increase dynamic range, but it would also help to ameliorate the matrix effects often encountered in complex hazardous waste samples. Although the foregoing needs in volve improvements to existing instru mentation, no progress in providing chromatographic interfaces for NMR systems has been forthcoming from the private sector, despite demonstrations of feasibility by the research communi ty (31-33). The high molecular selec tivity of NMR, the availability of large collections of NMR reference spectra, and the nondestructive nature of the technique make it a logical choice for quadrupole linkage. When a more com plete evaluation of the strengths and weaknesses of linked FT-IR/MS be comes available, the need for multicomponent NMR capability will be clearly defined and a potential instru mentation market should be revealed. A discussion of the instrumental needs of hyphenated quadrupoles should not omit the requirement for structural interpretation software. This need is particularly acute for quadrupoles linked to spectral detec tors. Some progress along these lines is already evident from the research com munity (34).
Future directions
In a world in which the number of new chemicals reported yearly is estimated at 4 Χ 105 (11), unique approaches will be required to delineate the environ mental risks posed to man. To be suc cessful, these approaches must be eco nomical and must rely heavily on auto mation. It is anticipated that complete characterization of environmental samples will be impractical and uneco nomical. What is needed is the ability to characterize the most abundant tox ic constituents, regardless of their vola tility or of the availability of authentic standards of these constituents. A pro posed and integrated approach to this goal includes the following steps. • Automated sample cleanup by ro botics or other suitable methods. • Inexpensive in vitro biological screening. Screening organisms should be chosen such that results can be extrapolated to humans. • Hyphenated QMS chemical analy sis of samples producing biological screen positives. • Computer-established molecular structure assignment from hy phenated QMS data. • Integration of final data into com puterized risk and hazard assess ment schemes (41). Each of these scheme components is the subject of ongoing research. Thus it may be time to consider what is neces sary to implement such an approach, or other suitable approaches, that can meet the challenge of potentially rapid increases in the complexity of environ mental contamination. Although the research described in this article has been supported by the Environmental Protection Agency, it has not been subjected to Agency review and therefore does not necessarily reflect the views of the Agency. No official endorsement should be inferred.
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Donald F. Gurka (left) received his B.S. degree from Columbia University and his Ph.D. degree in physical chemistry from the University of Washington. He is currently employed at EPA, where his research interests include the development of environmental assays, hyphenated techniques, FT-IR spectrometry, and linear free-energy relationships. John M. Henshaw (second from left) received his B.S. degree from Western Washington State College. Currently he is a chemist with Lockheed-EMSCO. His research interests include trace elemental analysis. L. Donnelly Betowski (third from left) received his B.S. degree from Georgetown University and his Ph.D. in physical chemistry from Cornell University. His interests as a research chemist at EPA include environmental applications of LCI MS/MS, LC/MS, and GC/MS. Edward M. Heithmar (fourth from left) received his B.A. degree from Biscay ne College (Miami) and his Ph.D. in analytical chemistry from the University of Pittsburgh. He is a research chemist at EPA, where his research interests include the development of trace elemental techniques using atomic absorption and plasma/mass spectrometry. Richard Titus (fifth from left) is professor of chemistry at the University of Nevada at Las Vegas. His research interests include hyphenated techniques, NMR, and organosulfur chemistry. Thomas A. Hinners did his undergraduate and graduate work at George Wash ington University and studied the work of Wolfgang Weber and Gerd Millier (DFB) in Germany. Since 1970 he has been involved in trace element studies of biological and environmental media.
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