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Anal. Chem. 1982, 5 4 , 2256-2260
(9) Horvath, Csaba; Melander, Wayne: Molnar, Imre; Molnar, Petra Anal. Chem. 1977. 49. 2295-2305. (10) Konljnendijk, A. P.; van de Venne, J. L. M. I n "Advances in Chromatography 1979"; Zlatkls, A., Ed.; Chromatography Symposium: Houston, TX 1979; pp 451-462. (11) van de Venne, J. L. M.; Hendrlkx, J. L. H. M.: Deelder, R . S.J. Chromatogr. 1978, 767, 1-16. (12) Wittmer, D. P.; Nuessle, N. 0.; Haney, W. G., Jr. Anal. Chem. 1975, 4 7 , 1422-1423. (13) Horvath, Csaba; Melander, Wayne; Molnar, Imre J. Chromatogr. 1976, 725,129-256. (14) Bidlingmeyer, B. A.; Deming, S.N.; Price, W. P., Jr.; Sachok, B.; Petrusek, M. J. Chromatogr. I97g, 786,419-434. (15) Deelder, R. S.;Linssen, H. A. J.; Kronijnendijk, A. P.; van de Venne, J. L. M. J. Chromatogr. 1979, 785,241-257. (16) Knox, John H.; Hartwick, Richard A. J. Chromatogr. 1981,204,3-21. (17) MukerJee, P.; Mysels, K. J. Natl. Stand. Ref. Data Ser. ( U S . , Natl. Bur. Stand.) 1971,No. 36. (18) Everett, D. H. Trans. Faraday SOC. 1964,6 0 , 1803-1813. (19) Everett, D. H. Trans. Faraday SOC. 1965,67, 2478-2495. (20) Locke, D. C. J. Chromatogr. Sci. 1974, 72,433-437.
(21) Lewis, G. N.; Randall, M. "Thermodynamics"; McGraw-Hili: New York, 1961; Chapter 20. (22) Elkoshi, 2 . ; Grushka, Ell. J. Phys. Chem. 1981,85,2980-2986. (23) Lucassen-Reynders, E. H. I n "Progress in Surface and Membrane Science"; Cadenhead, D. A., Danielli, J. F., Eds.; Academic Press: New York, 1976; Vol. IO, pp 253-3130, (24) Johnson, E. L.; Stevenson, R. "Basic Liquid Chromatography"; Varian: Palo Alto, CA, 1978; p 37. (25) Rosen, M. J. "Surfactants and Interfacial Phenomena"; Wiley: New York, 1978. (26) O'Neill, R. Appl. Statist. 1971,20,338-345. (27) Kong, R. C.; Sachok, 8.; Demlng, S. N. J. Chromatogr. 1960, 799, 307-316. (28) Davies, J. T.; Rideal, E. K. "Interfacial Phenomena"; Academic Press: New York, 1963; Chapter 4.
RECEIVED for review November 30, 1981. Resubmitted June 11, 1982. Accepted July 30, 1982. This work was supported in part by a grant from Chevron Research Co.
Determination of Nitrated Polycyclic Aromatic Hydrocarbons by Fused Silica Capillary Gas Chromatography/Negative Ion Chemical Ionization Mass Spectrometry Thomas Ramdahl"
and Kjell Urdal
Central Institute for Industrial Research, P.O. Box 350, Blindern, Oslo 3, Norway
Gas chromatography/electroncapture negatlve Ion chemical lonlzatlon mass spectrometry is shown to be a very sensltlve and Selective determlnatlon method for nltrated polycyclic aromatic hydrocarbons (PAH). The detectlon llmlt was 1 pg Injected to the GC column uslng slngle Ion monltorlng. The mass spectra are characterized by an intense molecular Ion, the base peak In all spectra. The second most abundant ions were (M 16)- and (M - 30)- for mono- and dlnltro-PAH, respectlvely. The NO,- Ion ( m / z 46) Is observed in most spectra. There are few dlfferences In the mass spectra of various Isomeric compounds. The pressure and the temperature In the ion source had llttle Influence on the mass spectra and sensitivity within the llmlts tested. The method is demonstrated on a synthetic mixture containlng nltro-PAH, and on a toluene extract of a formerly commercial carbon black. The appllcatlon to urban alr partlculate extracts Is discussed.
-
Nitro aromatic compounds can be readily formed by reaction between nitrogen oxides (NOx) and polycyclic aromatic hydrocarbons (PAH). Exposure of PAH adsorbed to different carriers to NOx has been shown to produce nitro-substituted reaction products which are directly mutagenic in the Ames Salmonella test (1, 2). Nitro-PAH have been identified in several environmental samples like air particulate matter (3, 4 ) , diesel exhaust particles (5),and carbon black (6). These findings suggest that nitro-PAH like PAH may be ubiquitous in the environment, but in comparatively lower concentration. Environmental samples are often extremely complex. The method of capillary gas chromatography (GC) has proved to be an extremely useful tool in analyzing multicomponent mixtures (7). Capillary GC is characterized by high sensitivity, excellent resolution power, and good reproducibility. Because
of the often very low level of nitroarenes in environmental samples, such a high resolution method is needed, but no satisfactory detection method has yet been devised. Capillary GC/MS and high-resolution mass spectrometry have recently been employed to determine nitro-PAH in diesel exhaust particles (5). Another recent approach by capillary GC is by using a nitrogen-selective detector (8). Here the identification was made by comparing the retention times with those of reference compounds. As the level of nitro-PAH in environmental samples is very low, a more sensitive and selective determination method is wanted. It is known that many nitro compounds exhibit strong response to the electron capture (EC) detector. The theoretical detection limit for an EC detector is estimated to 330 am01 (9). The ionization mechanisms of the EC detector and in methane (electron capture) negative ion chemical ionization mass spectrometry (ECNICIMS) are similar. Hunt and Crow have stated a 10- to 100-fold increase in sensitivity by ECNICIMS compared to the GC/ECD (10). Recent work on polyhalogenated hydrocarbons and mycotoxins shows the great versatility of this negative ion technique (11,12). These results indicate that ECNICIMS may be a very sensitive and selective method for the determination of nitro-PAH. The purpose of this study is to investigate the application of methane negative ion chemical ionization mass spectrometry to the determination of these compounds. EXPERIMENTAL SECTION GC/MS System. All spectra were recorded on a Finnigan Model 4021 quadrupole mass spectrometer equipped with a standard EI/CI source, Primary ionization of the CI reagent gas was accomplished with a 70-eV beam of electrons generated from a heated rhenium filament with an emission current of 0.25 mA. Methane was used as reagent gas, the ion source pressure was maintained at 0.15 torr, and source temperature was 250 "C, unless otherwise stated. The electron mulitplier voltage was 1700 V.
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Table I. Nitroarenes Used in the Present Study no.
abbreviation
compound
1
MNN 2-NB 3-NB 4-NB 2-NF 9-NA 2-NFO 4-NP 1-NP 2-NP 1,3-DNP 1,6-DNP l,&DNP 1,3,6-TNP 1,3,6,8-TNP
2-methyl-1-nitronaphthalene 2-nitrobiphenyl 3-nitrobiphenyl 4-nitrobiphenyl 2-nitrofluorene 9-nitroanthracene 2-nitrofluorenone
2 3 4 5 6 7
8
9 10 11
12 13 14 15
exptl sample, ng/&
ret time, MS (m in: s)
57.0 46.0 62.0 68.8 83 62.6 125 72.0 91.4 82.8 123.8 127.0 157.0 120.4 162.8
17:18 18:46 21:40 22:18 27:33 28:13 29:30 35:47 36 :28 36 :50 42:13 43:03 43:39 47:30 50:37
4-nitrop yrene
1-nitropyrene 2-nitropyrene 1,S-dinitropyrene 1,6-dinitropyrene 1,&dinitropyrene 1,3,6-trini trop yrene 1,3,6,8-te trani tropyrene
E1 spectra were recorded under identical conditions, without reagent gas. Sample introduction was accomplished by means of a Finnigan 9610 gas chromatograph directly interfaced to the mass spectrometer by the 30 m X 0 25 mm i.d. DB-5 fused silica capillary column (J & W Scientific, Inc.), film thickness 0.25 pm. Typical GC conditions were as follows: injector temperature, 280 "C; interface temperature, 240 "C; GC carrier gas, helium; flow rate, 40 cm/s at 100 "C; column temperature, 100-325 OC at 5 "Clmin. The initial temperature was held for 3 min. In the SIM mode the temperature program was 100-325 OC at 10 "C/min; the initial temperature was held for 2 min. The masses from 40 to 390 amu were scanneed every 1 s. The ion data were acquired by using an INCOS 2100 data system. GC System. A Hewlett-Packard 5730A gas chromatograph with an electron capture detector was used. The same 30-m DB-5 fused silica capillary coluinn as for NICIMS was employed with identical GC conditions. Chemicals. I-Methyl-1-nitronaphthalene, 2-, 3-, and 4nitrobiphenyl, 2-nitrofluorene, 9-nitroanthracene, and 1-nitropyrene were purchased from ICN Pharmaceuticals, USA. 2Nitrofluorene was contaminated with 2-nitrofluorenone and the latter is therefore included in the study. 2- and 4-nitropyrene were a gift from A. Berg, University of Aarlhus, Denmark. The polynitropyrenes were supplied by R. Mermelstein, Xerox Corp., USA. Extraction of Carbon Black. One gram of Mogul L Carbon Black (Cabot GmbH, W. Germany, produced before 1980) was extracted with toluene in a Soxhlet apparatus for 24 h. The extract, concentrated to 1 mL, was used without any further workup. RESULTS AND DISCUSSION Gas Chromatograplhy with EC Detector. Figure 1A presents the chromatogram of the standard mixture described in Table I by gas chromatography with EC detector (GC/ ECD). To be noted are the two compounds, 4-nitrobiphenyl (4-NB) and 2-nitropyrene (2-NP), which show less response than their respective isomers. 2-NP is showing approximately 15% response compared to the other nitropyrenes. There is some discrimination against high molecular weight compounds. This may be due to the injection system. To minimize this pnoblem, one should use the cold on-column injection technique (8, 23), but we had 110 access to such a system in this study. The GC/ECD system shows some tailing, and lower resolution than in the MS studies. This is in accordance with experiences previously reported by Grob, who found a smaller separation number for ECD than for FID (comparable to the MS system used) when analyzing 1-bromoalkanes (14). Gas Chromatography/Mass Spectrometry. ECNICI. When methane is used as the reagent gas in the negative mode, no reagent negative ionia are formed (10). Methane acts as a moderator, and a large population of thermal electrons is
A
10 00
LO 00
30 00
2 3 00
B
5000
TIME
I
I
L
_________
- 1 820
1640
2500
3320
~
LILO
5000 TIME
Figure 1. (A) Chromatogram of a standard mixture of nitro-PAH by GCIECD. (B) Reconstructed ion chromatogram of the same mixture by GC/ECNICIMS. For peak identities see Table I.
produced, which can be captured by high electron affinity molecules by resonance capture. A clear demonstration of this is shown in Figure 1, where the chromatogram from the GC/ECD analysis and the reconstructed ion chromatogram from the GC/MS analysis are compared. The two chromatograms are very similar, note the low response for 4-NB and 2-NP in the GC/MS trace, the same feature as observed in the GC/ECD trace. Little fragmentation is expected by this mechanism as the captured electrons have low energy. The limited fragmentation is presumably due to dissociative resonance capture. Factors affecting these mechanisms are the pressure and temperature in the mass spectrometer ion source (15, 16). ECNICI Mass Spectra of Nitroarenes. As expected, the ECNICI mass spectra showed little fragmentation compared to conventional electron impact (EI) mass spectra. Table I1 reports the abundance of the molecular ion for these two types of mass spectra. The molecular ion for all the nitro-PAH in
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ANALYTICAL CHEMISTRY, VOL. 54, NO.
13, NOVEMBER 1982 2L7
Table 11. Intensity of the Molecular Ion of the E1 and ECNICI Mass Spectra of Nitroarenes (Percent of Total Ion Current)
a
compound
E1
ECNICI
MNN 2-NB 3-NB 4-NB 2-NF 9-NA 2-NFO 4-NP 1-NP 2-NP 1,3-DNP 1,6-DNP l,&DNP 1,3,6-TP 1,3,6,8-TNP
11
74 71
2 21 21 16 13 18
14 14 19
L6 I " ' " " '
' ~ " " " ' l " ' " "
78
292
76
1°001 b
40
50 53 49 54
a
80 1000,
the ECNICI mass spectra contributes to over 50% of the total ions produced, over 70% for the mononitroarenes, compared to up to 20% in the E1 mass spectra. This reduced fragmentation is clearly favorable when performing single ion monitoring (17). Table I11 reports the ECNICI mass spectra of the nitro-PAH studied. The spectra are very characteristic, all showing the same fragmentation pattern. Figure 2 shows examples of the ECNICI mass spectra of mono-, di-, and trinitropyrenes. The mononitro compounds all have the molecular ion as base peak, indicating the great stability of this ion. The (M - 16)- ion (loss of an oxygen radical) was the dominant fragment. The NOz- ion ( m / z 46) is observed in all spectra, and this very characteristic fragment can contribute to the identification of unknown nitro-PAH. The three isomers of nitrobiphenyl show some differences that can be used to distinguish between them, the abundant m / z 46 ion for 2-NB and the abundant (M - 16)- ion for 3-NB. On the contrary, the three isomers of nitropyrene are indistinguishable, the mass spectra being almost identical. The dinitro compounds show the (M - 30)- ion (loss of a nitrite radical) as the dominant fragment, but also the (M 16)-, (M - 46)-, (M - 60)-, and m / z 46 fragment ions are characteristic. The mass spectra of the three dinitropyrenes are so similar that no positive identification can be made on the basis of the mass spectra only. The trinitro compound also shows the (M - 30)- ion as the most abundant fragment. The NOT ion ( m / z 46) was hardly observed. The tetranitro compound shows little fragmenta-
! c
50.0
i
N@z
NO2
Flgure 2. ECNICI mass spectra of
(a) 1-nitropyrene, (b) 1,3-dinitro-
pyrene, and (c) 1,3,64rinitropyrene.
tion, the (M - 16)- and (M - 30)- being comparable fragment ions. The discrimination of the GC system must also here be taken into consideration, very small amounts were introduced to the ion source. This although limited fragmentation makes it possible to distinguish between nitro-PAH and other electron-capturing compounds of similar polarity such as ketones and quinones (5) which show no fragmentation (18). Pressure Dependence of Spectra. The pressure in the ion source was varied in the range 0.1-0.3 torr. Above 0.3 torr the pressure in the analyzer region will exceed 1 X torr and the automatic protection for high vacuum failure will switch off the electronic system, hence the pressure range was limited. Within the range tested only small differences in the mass spectra were observed. The fragmentation seemed to decrease a little as the pressure was increased, while the total ion current did not change. Temperature Dependence of Spectra. Two different ion source temperatures were compared. At 165 "C the frag_ _ l _ _ _ l _ _ _
Table 111. Methane Electron Capture Negative Ion Chemical Ionization Mass Spectra of Nitroarenes (% Relative Abundance) compd mol wt M(M - 16)- (M - 30)- (M - 46)- (M - 60)-
2-NF
9-NA 2-NFO 4-NP 1-NP 2-NP 1,3-DNP 1,6-DNP 1,8-DNP 1,3,6-TNP 1,3,6,8-TNP a
Below 0.1%.
r
67
N o t determined.
MNN 2-NB 3-NB 4-NB
t
72 75
16 16 15
13
231
73 78
m/z 46
187
100
7
9
199 199 199
100 100
9 15 7
14 0.7 0.8
21 1 223 225 24 7 24 7 247 292 292 292 337 382
100 100 100 100 100
100
100 100 100
100 100
100
5 4 15 10 9 10 12 12 11
10 4
0.3 2
0.4 1.2 0.7
2
0.5
0.3 0.5 0.1
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ANALYTICAL CHEMISTRY, VOL. 54, NO. 13, NOVEMBER 1982
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Table IV. Nitroarenes Characterized in a Toluene Extract of a Former Commercial Carbon Black ( 2 0 ) % re1 abundance identity scan mol vvt M(M - 16)- (M - 30)- (M - 46)- n i / Z 46 nitronaphthalene 3 6 993 173 100 nitro aphthalene 3 173 100 1051 9-nitroanthracene 2 1771 6 10.0 223 unknown (mononitro) 5 100 243 77 1866 unknown (mononitro) 5 87 24 9 100 2022 unknown (mononitro) 100 0.4 249 78 7 2049 1-nitropyrene 3 2185 247 100 (nitrocyclopenta[~d]pyrene)~ 0.6 271 100 2468 1,3-dinitropyrene 4 19 1 0.5 100 292; 2529 1,6-dinitropyrene 7 19 2 0.4 100 292 2581 1,8-dinitropyrene 6 26 2 0.5 100 292 2614 unknown (dinitro) 12 0.6 2 100 298 2646 l13,6-trinitropyrene 100 337 2953 a
Or other isomer.
-
BLANK
2Lh
2PG 2-METHYL-1-NITRONAPHTHALIENE RIC
,LO
320
520
6Lo
820
1000
IlLOTlME
Figure 3. Response obtained by monitoring the M- ion ( m / z 187) of 2-methyl-I-nitronaphthalene with the instrument running in the SIM mode. mentation was about 5% less than at 250 "C, and we did not observe the temperature dependence of the spectra as reported for other compounds (11, 12). However, tri and tetranitropyrene could not be detected at 165 "C. At this low temperature the high boiling compound will probably condense in the ion source region. The total ion current for the more volatile compounds was about the same at both temperatures. Detection Limit. By use of single ion monitoring on the molecular ion 2 pg of 2-methyl-1-nitronaphthalene gave a signal to noise ratio greater than 100. Three subsequent injections showed a standard deviation of 4%. Below this level there was a sharp drop in sensitivity, and a detection limit of 1 pg was established. A blank sample was injected just before and after the samples, and no signal was then registered. The reconstructed ion chromatograms of the blank and the sample are shown in Figwe 3. The detection limit of the high boiling compounds will be at a higher level. This is probably due to the column/injection port system which is not totally inert. Applications. Synthetic Sample. The sensitivity and selectivity of the ECNICI method are demonstrated in Figure 4. It shows a mixture of PAH spiked with a selection of mononitro-PAH. The amount injected of individual compounds ranged from 1to 25 ng for PAH anid from 200 pg (peak 5) to 400 pg (peak 7) of nitro-PAH. Figure 4A shows the reconstructed ion chromatogram under ECNICI conditions, and Figure 4B under E1 conditions. The nitro-PAH not detectable in the E l run are easily determined by the ECNICI technique. This demonstrates the great versatility of the method. The samples are run in the full scan mode, and good mass spectra are obtained for each of the nitro compounds, despite their relatively low amount. In the E1 run the low abundant ions
.820
16LO
25.00
33 20
LlLO
5000
TIME
Figure 4. Reconstructed ion chromatograms of a mixture of PAH splked with nitro-PAH: (A) ECNICI condition; (B) E1 conditions. For peak identities see text and Table I. originating from the nitro compounds are hidden by the ions from the PAH, present in much higher abundance. The electron capture process is competitive. If two components are in the ion source at the same time, the one with the largest electron capture cross section will get the most electrons. The sensitivity of the method when analyzing a real sample may be less than analyzing a standard sample, as some compounds may coelute in the real sample. Bjerrseth and Eklund (19) have recently reported that several PAH have considerable electron capture properties. This is most markedly shown in Figure 4 by indeno[l,2,3cdlpyrene (peak b). Also note the response of fluoranthene (peak a) and not of the isomer pyrene, which coelutes with 2-NF (peak 5). This is in agreement with the EC results (19).
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Anal. Chem. 1982, 5 4 , 2260-2264
Carbon Black. Table IV reports the analysis of the toluene total extract of a carbon black similar to that recently described by Rosenkranz et al. as Carbon black B (20). In addition to the reported nitropyrenes, several other nitroarenes were determined. In this sample the level of nitro compounds was relatively high. The ECNICI technique proves to be a very rapid and sensitive screening method for such samples, as no workup of the total extract is needed. Urban Air Particulate Matter. The present method has also been applied to determine nitro-PAH in extracts of urban air particulate matter. After fractionation of the extract by normal phase silica high-performance liquid chromatography, the occurrence of 1- and 2-nitronaphthalene, two isomers of nitroanthracene, methylnitroanthracene, 3-nitrofluoranthene, and l-nitropyrene was demonstrated in the moderately polar fraction by the ECNICI technique. A detailed discussion of this application is given elsewhere (21). ACKNOWLEDGMENT The authors are indebted to R. Mermelstein, Xerox Corp., USA, for the gift of di-, tri-, and tetranitropyrene, and to A. Berg, University of Aarhus, Denmark, for the gift of 2- and 4-nitropyrene.
(4) Wang, C. Y.; Lee, M.-S.; King, C. M.; Warner, P. 0. Chemosphere 1980, 9.83-87. (5) Schuetzle, D.; Lee, F. S.-C.; Prater, T. L.; Tejada, S . B. Int. J . Environ. Anal. Chem. 1981, 9 , 93-144. (6) Fitch, W. L.; Everhart, E. T.; Smlth, D. H. Anal. Chem. 1978, 5 0 , 2122-2126. (7) Bertsch, W., Jennings, W. G., Kaiser, R. E., Eds. "Recent Advances in Capillary Gas Chromatography", A. Hutig Verlag: Heidelberg, 1981. (8) Ramdahl, T.; Kveseth, K.; Becher, G. HRC CC,J . High Resolut. Chromatogr. Chromatogr. Commun. 1982, 5 , 19-26. (9) Pelllzzari, E. D. J . Chromatogr. 1974, 98, 323-361. (IO) Hunt, D. F.; Crow, F. W. Anal. Chem. 1978, 50, 1781-1784. (11) Crow, F. W.; Bjmrseth, A.; Knapp, K. T.; Bennet, R. Anal. Chem. 1981, 53, 619-825. (12) Brumley, W. C.; Nesheim, S.; Trucksess, M. V.; Trucksess, E. W.; Dreifuss, P. A.; Roach, J. A. G.; Andrzejewski, D.; Eppley, R. M.; Pohland, A. E.; Thorpe, C. W.; Sphon, J. A. Anal. Chem. 1981, 5 3 , 2003-2006. (13) Grob, K., Jr.; Neukom, H. P. J . Chromatogr. 1980, 189, 109-117. (14) Grob, K. Chromatographia 1975, 8 , 423-433. (15) Smit, A. L. C.; Field, F. H. J . Am. Chem. SOC.1977, 99, 6471-6483. (16) Bruins, A. P. "Advances in Mass Spectrometry"; Quayle, A,, Ed.; Heyden: London, 1980; Vol. EA, pp 246-254. (17) Garland, W. A.; Powell, M. L. J . Chromatogr. Sci. 1981, 19, 392-434. (18) Hunt, D. F.; Stafford, G. C., Jr.; Crow, F. W.; Russel, J. W. Anal. Chem. 1976, 4 8 , 2098-2105. (19) BjDrseth, A.; Eklund, G. HRC CC, J . High Resoiut. Chromatogr. Chromatogr. Commun. 1979, 2 , 22-26. (20) Rosenkranz, H. S.; McCoy, E. C.; Sanders, D. R.; Butler, M.; Kiriazides, D. K.; Mermelsteln, R. Science 1980, 209, 1039-1043. (21) Ramdahl, T.; Becher, G.; Bj~rseth,A. Environ. Sci. Technoi., in press.
LITERATURE CITED (1) Pltts, J. N., Jr.; van Cauwenberghe, K. A,; Grosjean, D.; Schmid, J. T.; Fitz, D. R.; Belser, W. L., Jr.; Knudson, G. B.; Hynds, P. M. Science 1978, 202, 515-519. (2) Hirayama, T.; Nohara, M.; Shindo, H.; Fukui, S. Chemosphere 1981, IO, 223-228. (3) Jager, J. J . Chromatogr. 1978, 15.2,575-578.
RECEIVED for review April 2, 1982. Accepted July 29, 1982. This work was supported by a grant from the Royal Norwegian Council for Scientific and Industrial Research under Contract No. 0106.08147.
Mixture Analysis by Gas Chromatography/Fourier Transform Infrared Spectrometry/Mass Spectrometry Charles L. Wilkins," Gary N. Giss, Robert L. White, Gregory M. Brlssey, and Emmanuel C. Onylrluka Department of Chemistry, University of California -Riverside,
Riverside, California 9252 1
Use of complementary Information obtalned from a SCOT column gas chromatography system directly linked with a Fourier transform infrared spectrometer and a mass spectrometer for analysls of two complex mixtures, peppermint oll and a lacquer thinner, has been lnvestlgated. These mixtures, each with more than 30 components, are, by far, the most complex mlxtures thus far analyzed with such a dlrect-linked system. Both a double-focuslng sector mass spectrometer and a Fourier transform mass spectrometer have been used in the present work. Both approaches have been shown to offer advantages for the structural determlnatlon of mixture components.
Continuing improvements in gas chromatography/Fourier transform infrared (FT-IR) spectrometers have resulted in making capillary column GC/FT-IR a practical analytical tool. Primarily as a result of development of improved lightpipes and low dead volume interfaces, useful vapor-phase infrared spectra of compounds present in quantities as small as 10-100 ng can now be obtained "on-the-fly". Several recent presentations have documented these facts (1-4). Early last year, we reported our successful demonstration of a direct-linked
gas chromatography/Fourier transform infrared/mass spectrometer (GC/FT-IR/MS) system employing a packed GC column for the analysis of some simple model mixtures ( 5 ) . As expected, the complementary information thus available permitted accurate computer-aided identification of the substances examined in cases where either technique (GC/ FT-IR or GC/MS) alone would have provided inconclusive results. Others have also obtained such results with GC/ FT-IR/MS systems (6,7). Because we recognize that capillary column gas chromatography is necessary to provide the required chromatographic resolution for separation of more complicated mixtures, we have subsequently investigated the use of both SCOT and fused silica capillary columns for GC/FT-IR/MS. Preliminary accounts of our analysis of peppermint oil using a SCOT capillary column linked with a Nicolet 7199 FT-IR system and a Kratos MS-80 mass spectrometer were presented late last year (8, 9). More recently, Crawford et al. have described their results (IO)with a linked GC/FT-IR/MS system also using a SCOT column and essentially the same approach we described for our earlier packed column work ( 5 ) . Although analysis of simple model mixtures is worthwhile for initial evaluations, it is obvious that practical analyses will very often involve many more than four or five components
0003-2700/82/0354-2260$01.25/00 1982 American Chemical Society
