Application of a Gas Chromatograph-Mass Spectrometer-Data Processor Combination to the Analysis of the Polycyclic Aromatic Hydrocarbon Content of Airborne Pollutants R. C. Lao, R. S. Thomas, H. Oja, and L. Dubois Chemistry Division, Technology Development Branch, Air Pollution Control Directorate, Department of the Environment, Ottawa, Canada K 1 A OH3
A gas chromatograph-mass spectrometer-data system has been utilized to measure polynuclear aromatic hydrocarbons (PAH) in air samples. Airborne particulate samples were collected on glass fiber filters using a high volume sampler. The filters were soxhlet-extracted using cyclohexane, and extractable matter was subjected to a Rosen separation. The PAH fraction was concentrated and injected into the GC-MS system. For each GC peak, mass spectra were obtained and compared to PAH reference standards. More than 7 0 major PAH having from two to seven rings were separated and identified in an air sample. Samples of less than 100 pg produced good data, for the individual components emerging from the column in amounts in the nanogram region.
In recent years the combination of gas chromatography (GC) and mass spectrometry (MS) has seen increasing use as a versatile tool for in-depth analytical studies of environmental problems. The number of applications of this technique are reviewed in periodic publications ( I , 2). The fundamental nature of MS removes many of the ambiguities inherent in analytical GC which must rely solely on retention time and detector response data for the information as to compound identification. Gas chromatography as an analytical technique is severely limited by the scarcity of standard reference materials which must be available if a method is to be properly standardized. The use of a MS, as the GC detector, removes this shortcoming by allowing the identification of individual components eluted from the gas column in terms of their mass spectra. Although the GC analysis of polycyclic aromatic hydrocarbons (PAH) in urban airborne particulates has been described by a number of workers (3-7), chromatographic methods alone are not able to provide a complete analysis of the complex mixtures of PAH encountered in pollution studies. Despite the importance of the PAH having five or more rings, as air pollutants, only cursory attention has been given to the mass spectra of individual compounds. A continuing program to obtain standard mass spectra for these compounds (8, 9) and to evaluate the potential of ( 1 ) Gas Chromatography-Mass Spectroscopy Abstracts, Science and Technology Agency, London, 1972. (2) Anal. Chem., 44, (Reviews issue), pp 213R-41R, 337R-79R (1972). (3) E. Sawicki, "Analysis of Airborne Particulate Hydrocarbons." Nat. Cancer Inst. Monogr., 9, 201 (1962). (4) D. Hoffman and E. IL'Wynder in "Air Pollution." 2nd ed., Academic Press, N e w York, N . Y . , 1968, p 187. (5) Anal Chem., 43, (Reviews Issue), 1R (1971). (6) J . R . W i l m s h u r s t , J. Chromatogr., 17, 50 (1965). (7) V. Cantuti, G . V . Cartoni, and A. Liberti, J. Chromatogr., 15, 141 (1964); 17, 60 (1965). (8) R. C. Lao, J . L. Monkman. and R . F. Pottie, Proc. Int. Syrnp. Identif. Meas. Environ. Poliut.. Ottawa. Canada. 1971. D 144. ( 9 ) R C Lao. R S Thomas, and J L Monkman. lnt. J Envfron Anal. Chem 1 , 187 (1972)
908
ANALYTICAL CHEMISTRY, VOL. 45, NO. 6 , MAY 1973
GC-MS as a standard reference method for the analysis of PAH has been in progress.
EXPERIMENTAL The GC-MS system used in this work consists of a PerkinElmer 990 model gas chromatograph interfaced to a differentially pumped Hitachi RMU-6L single focusing mass spectrometer with electron impact source. A Markey type Biemann-Watson molecular separator (10) is used as the interface. Both packed and surface coated open tublar (SCOT) columns were evaluated. Operating conditions are summarized in Table I. Columns were conditioned a t 350 "C for 24 hours. No evidence of column bleeding was observed at sustained oven temperatures of 295 "C during the GC runs. The final temperature was maintained 50 minutes to ensure the complete elution of the seven-ring compounds such as coronene and dibenzpyrenes. The M S is scanned from about 14 to 350 amu a t either 20 amu or 60 amu/sec depending on GC peak residence time in the ion source. The accelerating voltage is 3.5 kV and the electron energy is 70 eV. The resolution of MS for GC-MS runs is about M/AM = 2,000 with ion source pressure maintained a t about 3 X Torr. A Perkin-Elmer PEP 1 GC data system was used to measure relative retention times (RRT) and calculate peak areas. Airborne particulate samples were collected on glass fiber filters using a commercial high volume sampler. Some 1500 m3 of air were pulled through each filter which had been weighed prior to sampling. The exposed filters were removed from the samplers, allowed to equilibrate a t standard conditions, and reweighed to determine the weight of entrained particulate material. Aliquot areas from these filters were extracted in Soxhlet extractors with cyclohexane for about eight hours,. The cyclohexane soluble matter was then submitted to a Rosen separation (11, 12) over fully activated silica gel to isolate the PAH fraction from the aliphatic and heterocyclic compounds. The PAH fraction was concentrated about 100-fold and injected into the GC-MS system. For each GC peak, mass spectra were obtained and compared to over 40 primary PAH standards of known purity (13). Synthetic quantitative mixtures of PAH were prepared to verify each stage of GC-MS operations and to standardize the data processing parameters such as response thresholds and time windows for peak identification. Since fluoranthene has been found to be present in all air samples and since it is eluted from the GC column as a pure isolated compound, free from interfering contaminants, it was selected as the internal reference for both RRT and response factors (RF).
RESULTS GC parameters of the PAH reference standards, as measured on the Dexsil 300 packed column, are given in Table 11. The gas chromatograms are shown in Figures 1 and 2 and the relevant data are given in Tables In and IV. The response factors (RF) relative to fluoranthene, from Table 11, were used to calculate the per cent concentration of the air sample. Compounds whose RF values are not (10) S. P. Markey, Anal. Chem.. 42, 306 (1970). (11) G. E. Moore, R . S. Thomas, and J . L. Monkman, J. Chromatogr., 26, 456 (1967). (12) A. A. Rosen and F. M . Middleton, Anal. Chern., 27, 790 (1955). (13) R. S. Thomas and J . L. Monkman. CD Report No. 215, Chemistry Division, Technology Development Branch, Air Pollution Control
Directorate, Department of Environment, Ottawa, Canada, January 1972.
Table I . Chromatographic Operating Conditions SCOT column Packed Column Detector FID FID Detector temperature 300 " C 300 "C Liquid sample
volume Sample injector temperature Column
Carrier gas flow GC/MS split ratio Initial temperature Programmed temperature Final temperature
0.5 fiI
325°C 12 feet long, 0.1 25 inch in diameter, stainless steel packed with 6% Dexsil 300 on 80/ 100 mesh Chromosorb W (HP) Helium 40 ml/min 9:l 165 "C held for 2
minutes 4 "C/min 295 "C held for 50
minutes Recorder attenuation GC/MS interface temperature
0.2 UI
325 "c 35 feet long, 0.02 inch in diameter, stainless steel coated with 2% Dexsil300
Table I1 (Continued) Compound name
1-Methyl-pyrene Benzo [c] phenanthrene
Benzo [ghi] fluoranthene Benzo [a] anthracene Chrysene Triphenylene 4-Methyl-benzo [a] anthracene 1 -Methyl-chrysene 6-Methyl-chrysene /?,/?'-Binaphthyl 7,12-Dimethyl-benzo [ a ] anthracene
4 ml/min 1:l 165 "C held for 2
minutes 4 "C/min 295 " C held for 80
minutes
160 and 640
160
325 " C
325 " C
Table I I . Retention Time and Response Factor Data of Primary PAH Standards on Dexsil-300 Packed Column Relative Response Ring Indexa retention timeb factorb Compound name 0.21 1 0.751 Biphenyl ls2,3,4,5,6,7,8-0cta3618 0.250 hydro-anthracene 0.776 Benzindene 31 28 0.388 0.81 0 3127 0.41 2 Fluorene 0.864 9,lO-Dihydro-phenan3619 0.473 threne 0.827 9, 1 O-Dihydro-anthra3618 0.499 0.803 cene 31 27 2-Methyl-fluorene 0.546 0.916 31 27 1-Methyl-fluorene 0.555 0.916 31 27 9-Methyl-fluorene 0.603 0.916 3619 Phenanthrene 0.648 0.920 3618 Anthracene 0.664 0.880 3521 Benzoquinoline 0.688 0.926 3523 0.708 Acridine 0.918 2-Fluorene carbo31 27 0.733 0.926 nitrile 3-Methyl-phenan3619 0.790 threne 1.042 2-Methyl-phenanthrene 3619 0.795 1.042 2-Methyl-anthracene 361 8 0.806 0.998 Dihydro-pyrene 5262 0.962 0.962 Fluoran thene 1.000 4799 1,000 Pyrene 5262 1.064 1.067 Benzo [ a ] fluorene or 1 ,P-benzofI uorene 4776 1.153 1.137 Benzo [ b ] fluorene or 2,3-benzofluorene 4773 1.172 1.137 Benzo [ c ] fluorene or 3.4-benzofluorene 4780 1.177 1.137 2-Methyl-fluoranthene 4799 1.193 1.070 4-Methyl-pyrene 5262 1.196 1.144 3-Methyl-pyrene 5262 1.235 1.142
9,lO-Dimethyl- benzo [ a ] anthracene
Benzo
IndexG 5262 5255 6092 5253
Ring
Relative
Response
retention timeb
factorb
1.233 1.342 1.406 1.418 1.428 1.432
1.138 1.238 1.250 1.245 1.239 1.242
...
1.545 1.553 1.565 1.582
1.328 1.334 1.321 1.267
5253
1.636
1.424
5253
1.631
1.436
6078
1.698
1.293
6075
1.743
1.426
6070 6399 6400 6401 6084
1.748 1.853 1.851 1.892 1.985
1.330 1.322 1.331 1.332 1.337
6381
2.295
1.342
6383 6379
2.304 2.440
1.342 1.348
5262 6384 5253 7036 7033 7392 7030 7026
2.418 2.457 2.499 2.595 2.574 3.523 3.592 3.592
1.354 1.354 1.351 1.356 1.350 1.483 1.485 1.481
5254
5256 5253 5254 5254
[ j ] fluoran-
thene Benzo [k]fluoranthene Benzo [ b ] fluoran-
thene Benzo [a] pyrene Benzo [e] pyrene Per y le ne 3-Methyl-cholanthrene 1,2,3,4-Dibenzanthracene 2,3,6,7-Dibenzanthracene Benzo [ b ] chrysene o-Phenylenepyrene or 2,3-phenylenepyrene Picene Benzo [ c ] tetraphene Benzo [ghi] perylene Anthanthrene Coronene 1,2,3,4-Dibenzpyrene 1,2,4,5-Dibenzpyrene
a See A. M. Patterson, L. T. Capell, and D. F. Walker. "The Ring Index," Amer. Chem. SOC.,Washington, D.C., 2nd ed., 1960, supple. 1 , 1963, Supple. 2. 1964. and supple. 3, 1965 Relative to fluoranthene.
available, because of the lack of standards, are assigned a value. For example, geometric isomers of PAH, having the same molecular weight, are assumed to have the s a m e RF value. For compounds with substituted alkyl groups or hydro derivatives, the RF values are estimated from those of PAH standards which have one or more corresponding group additions or substitutions. In general, a methyl group will increase the RF of the PAH by 6-8%, the addition of one extra hydrogen into the molecule decreases the RF value by &?%. S o m e of the mass spectra obtained are shown in Figure 3 through Figure 8. The upper sections are the spectra obtained from the PAH reference standards representing the average of ten runs with a standard deviation of about 5%, the lower sections are mass spectra of the GC effluent peaks. These spectra were chosen because m a n y of these compounds had not been reported previously (Figures 3 a n d 6) or were tentatively identified without confirmation (Figures 4 , 5 a n d 9). Figure 8 shows t h e mass spectrum of GC peak number 80, a mixture of BaP a n d BeP unresolved by either GC column. The upper sections are the reference spectra of t h e individual components and reveal the essentially identical mass spectral fragmentation patterns. However, the A N A L Y T I C A L CHEMISTRY, VOL. 45, NO. 6, M A Y 1973
909
Table 111. PAH Concentration of Air Sample on Dexsil-300 Packed Column Time, min
concn,a Area
RRT
RF
Pug
Peak
No.
0.751 0.776
0.0941 0.0163
1 la
0.271 0.293 0.325 0.340 0.380 0.395 0.425 0.469 0.484 0.536 0.570 0.617 0.648 0.658 0.694 0.706 0.726 0.759 0.784 0.816 0.841
0.758 0.758 0.796 0.796 0.810 0.810 0.864 0.827 0.803 0.916 0.916 0.916 0.920 0.880 0.926 0.918 0.926 0.926 1.042 0.998 1.185
0.0330 0.0171 0.0245 0.0098 0.0131 0.0147 0.0242 0.0556 0.0305 0.0405 0.01 36 0.0576 0.6102 0.5252 0.6899 0.6745 0.1082 0.0270 0.5825 0.5985 0.8691
lb 2 2a 3 3a 3b 4 4a 4b 4c 4d 5 7 11 12 13a 14 16 19 20
2.6867
0.866
1.132
1.0451
22
18.68 19.16 19.82 20.23 20.80 21 3 7
0.9678 0.2560 0.5863 0.3517 45.5014 6.6707
0.898 0.921 0.952 0.972 1.000 1.037
0.882 0.941 0.902 0.962 1.000 1.025
0.2949 0.0832 0.1826 0.1 168 15.7200 2.3624
24 24a 25 25a 27 29
22.13 23.05 23.61 24.20
45.8240 1.6896 6.5088 11.6550
1.063 1.108 1.135 1.163
1.067 0.996 1.137 1.137
16.8904 0.5813 2.5566 4.5780
32 35 36 38
24.87 25.49 26.27
5.8873 6.6473 1.4477
1.195 1.225 ,262
1.070 1.142 ,291
2.1 762 2.6224 0.6456
40 42 44
26.89 27.89
1.3720 22.869 7
,292 ,340
,090 ,238
0.5166 9.7808
46 48
28.47 29.08
8.6316 6.2800
,368 ,398
,250 ,108
3.7276 2.4037
51 53
29.94
104,2432
,439
,241
44.6912
55
30.38
2.3440
,460
,212
0.9814
58
30.83
2.6595
,482
,153
1.0593
59
31.14 31.65 32.23 32.59 32.93
3.1209 0.8637 13.5014 2.7044 3.7072
,497 ,521 ,549 ,566 1.583
,328 ,328 ,328 ,267 1.269
1.4318 0.3963 6.1948 1.1838 1.6251
61 62 64 66 67
33.39 33.71
0.1104 0.1968
1.605 1.620
1.356 1.421
0.9169 0.0966
68 68a
34.35 35.20
0.2316 4.3513
1.651 1.692
1.420 1.293
0.1136 1.9437
69 70
4.43 5.27
0.3630 0.0609
0.212 0.253
5.65 6.10 6.76 7.08 7.91 8.22 8.85 9.76 10.08 11.15 11.86 12.85 13.44 13.70 14.45 14.70 15.11 15.80 16.32 16.99 17.50
0.1261 0.0656 0.0892 0.0356 0.0468 0.0526 0.0814 0.1949 0.1101 0.1280 0.0431 0.1822 1.9199 1.7279 2.1566 2.1271 0.3383 0.0846 1.6182 1.7360 2.1228
18.03
910
ANALYTICAL CHEMISTRY, VOL. 45, NO. 6, MAY 1973
I C
Compound nameb Biphenylb Octahydro-phenanthrenec and octahydro-anthraceneb,c Dihydro-fluorenec Dihydro-fluorenec Methyl-biphenyl Methyl-biphenyl Benzindeneb Benzindeneb Fluoreneb Dihydro-phenanthrenebvc Dihydro-anthracenebSC 2-Methyl-fluoreneb 1-Methyl-fluoreneb 9-Methyl-fluoreneb Phenanthreneb Anthraceneb Benzoquinolineb Acridineb Fluorene carbonitrilebvc Fluorene carbonitriledb-c Meth yl-phenanthreneb Methyl-anthraceneb Ethyl-phenanthrenec and dimethyl-phenanthreneC Ethyl-anthracenec and dirnethyl-anthracenec Octahydro-fluoranthenee Octahydro-pyrenec Dihydro-fluoranthenee Dihydro-pyrenebvc Fluorantheneb Dihydro-benzo[a] fluoreneC and dihydro-benzo [b] fluoreneC Pyreneb Dihydro-benzo [ c ] f I uoreneC Benzo [ a ] fluoreneb Benzo [b] fluoreneb and benzo [ c ] floureneb MethyI-fluoranthene* Methyl-pyreneb Trimethyi-fluoranthenec and trimethyl-pyrenec Dihydro-benzo [ c ] phenanthreneC Benzo [ c ] phenanthreneb and hexahydro-chrysenec Benzo [ghi] fluorantheneb Dihydro-benzo [a] anthracene,c dihydro-chrysene,c and dihydro-triphenyleneC Benzo [ a ] anthracene,b chrysene,b and triphenyleneb Tetrahydro-methyl-benzo [ a ] anthracene,c chrysene,c and triphenyleneC Dihydro-methyl-benzo [ghi] fluoranthenee Methyl-benzo [ a ] anthraceneb Methyl-triphenylene Methyl-chryseneb P,P'-Binaphthyib Dihydro-methyl-benzo [k&b] fluoranthenesC and dihydro-methyl-benzo [aae] pyrenesc Methyl-P$'-binaphthyIC Dimethyl-benzo [ a ] anthracene*J and triphenyleneC Dimethyl-chrysene' Benzo [ j ] fluorantheneb
Table I l l (Continued) Time, mln
Area
R RT
RF
Concn,a !Jg
Peak No.
Compound name'
Benzo [ k ] fluorantheneband benzo [ b ] fluorantheneb Methyl-benzo [ k ] fluoranthene and methyl-benzo [b] fluoranthene Benzo [ a ] pyrene,b benzo [e] pyreneb Peryleneb 3-Methyl-cholanthreneb Methyl-benzo [ a ] pyrene and methyl-benzo [e] pyrene
36.61
71.4393
1.760
1.333
32.8984
72
37.63
3.5564
1.809
1.426
1.7520
77
38.47 39.46 40.26 41.52
32.5593 4.7083 1.9296 1.7861
1.849 1.897 1.935 1.996
1.327 1.332 1.337 1.419
14.9268 2.1666 0.891 2 0.8756
80 a3 85 87
42.83 44.61
0.3621 0.6191
2.059 2.144
1.252 1.526
0.1566 0.3264
90 91
45.72
1.2694
2.198
1.519
0.6661
93
46.51 47.59 49.90
2.8792 3.1 700 14.0870
2.236 2.287 2.399
1.342 1.342 1.352
1.3348 1.4697 6.5796
94 97 100
1,2,3,4-D1benzanthraceneb 2,3,6,7-Di benzanthraceneb Benzo [b] chryseneb and
51.66 53.54
0.2106 8.1548
2.483 2.574
1.353 1.353
0.0984 3.81 19
105 107
o-phenylenepyreneb Piceneb and benzo [c]tetrapheneb Benzo [ghi] peryleneb and anthanthreneb
55.67 57.71 58.35
0.0897 0.3199 0.1582
2.676 2.745 2.805
1.340 1.436 1.447
0.0415 0.1587 0.0791
111 115 117
Methyl-o-phenylene-fluoranthenee
63.97
0.2541
3.075
1.447
0.1270
119
Methyl-o-phenylene-pyrenee
69.84
0.3495
3.357
1.448
0.1748
122
72.61 74.16
2.4440 2.6548
3.490 3.565
1.483 1.483
1.2522 1.3621
123 124
o-Phenylene-fluoranthene Dimethyl-benzo [ k l fluorantheneCand dimethyl-benTo [b] fluoranthenee Dimethyl-benzo [ a ] pyreneCand
dimethyl-benzo [e] pyrenee
Methyl-dibenzanthracenee Methyl-benzo [ b ] chryseneCand methyl-benzo [c] tetraphenee and methyl-picenec Methyl-benzo [ghi] peryleneC and methyl-anthanthrenec Coroneneb Dibenzpyreneb
a Calibrated with fluoranthene the specific response is 0.3455 fig/unit area. Determined by comparison with a primary standard compound of known purity with respect to relative retention time and mass spectrum.
C
quantitative measurement of each component of such mixtures can be carried out by mass spectrometry when necessary (81. The presence of several low molecular weight nitrogencontaining compounds in the aromatic fraction suggests that the Rosen separation has some limitations (12). No molecules of heterocyclic character with molecular weight in excess of m / e 191 were found in the aromatic fraction.
atives of PAH. Thus octahydro phenanthrene (peak No. 1A) elutes before dihydrophenanthrene (No. 4) which precedes the parent compound phenanthrene (No. 5 ) while the normal order is followed by the methyl derivatives of pyrene peaks (42 and 44). Among the compounds represented in Figure 1, separation is not always complete. The isomers fluoranthene and pyrene are completely separated, but the isomers anthracene and phenanthrene are only about 60% separated. We also have the usual mixture of benzanthracene, chrysene, and triphenylene which does not separate by GC any better than by liquid column chromatography ( 2 4 ) . This mixture often amounts to some 20% of the total measured PAH fraction of the air sample. One might downgrade the importance of this mixed peak if it consisted only of triphenylene and chrysene. However, benzo[a]anthracene is a carcinogen. As in the case of the BaP and BeP mixture, the quantitative measurement of each component of the mixture can be performed by mass spectrometry (8). It is pleasing to note that a considerable number of the peaks, perhaps 20, are unique and unequivocally identified. It is also of more than passing interest to see that benzoti]fluoranthene (peak No. 7 0 ) , a carcinogen, is present as a completely separated peak to the extent of 2%. It may be the first time that hydro derivatives have been reported in air samples. These compounds constitute about 15%of the total measured PAH fraction. SCOT Column. The gas chromatogram obtained from this column as shown in Figure 2 is almost identical with the one obtained from the packed column. The separation was better for the range from fluoranthene to methyl chrysene as several new peaks, l l a , 20a, 35a, 43, 44a, 46a, and 53a in Table IV, were observed. However, the resolu-
DISCUSSION Of the two GC columns investigated in this work, the packed column yielded better results. During the 80-minute run, more than 100 compounds were resolved sufficiently to permit mass spectral identification and quantitation by area integration. Many of the peaks identified from their mass spectra have never been reported as constituents of airborne particulate matter. The final temperature of the programme, 295 "C, completely eluted coronene, the highest molecular weight PAH generally found in air. An extended final temperature time of 60 minutes failed to detect any further compounds beyond coronene, and the calculations of relative percentages are based on the assumption that all components had been eluted. Scrutiny of the sequence of chromatographic separations has revealed a regularity of behaviour which could not be observed during liquid column chromatography of these compounds (14). The hydro derivatives of PAH, in every case, elute before the parent compound. The degree of a hydrogenation is directly proportional to a reduction in retention time compared to the parent compound. This is the reverse of the observed elution order for alkyl deriv(14) L. Dubois and J. L. Monkman, J. Chromatogr., 28, 317 (1967)
Cornpcbunds found in the air sample which have not been previously reported.
ANALYTICAL C H E M I S T R Y , VOL. 45, NO. 6, M A Y 1973
911
55
b
81
4
48 57
1
n 7
i o min.
PO
30
Figure 1. Gas chromatogram of air sample on Dexsil-300 packed column
I8
55
'3
80
3P
i7
63
38
66
I
33
do min.
50
1
40
5
8
30
Figure 2. Gas chromatogram of air sample on Dexsil-300 SCOT column 912
ANALYTICAL CHEMISTRY, VOL. 45, NO. 6, MAY 1973
1
PO
iomin.
1
1oQ
9,lO-Dihydrophenanthrene
100
4,i-Dimothyl
1
phenanthrene
I
60-
x
x
20-
: p
I....
; 3
1111
.A
100:.
e l .
1
100-
I
Peak no. 4
i
20-
,ll,i.,
i
.-
I
111
B
E
60-
I 0
100
50
110
SO
200
100
210
200
150
mb
mle
Figure 3. Mass spectra of GC effluent peak No. 4 of air sample and the corresponding reference compound
Figure 6. Mass spectra of GC effluent peak No. 20 of air sample and the corresponding reference compound
100
3-Methyl
60
phenanthrene
1
1
1
1I
I ::
:: a o 0 S
I1
I
1 loo-'
