2078
Anal. Chem. 1988, 58, 2078-2084
Gas Chromatographic Chemiluminescent Detection and Evaluation of Predictive Models for Identifying Nitrated Polycyclic Aromatic Hydrocarbons in a Diesel Fuel Particulate Extract Albert Robbat, Jr.,* Nicholas P. Corso, and Philip J. Doherty' Chemistry Department, Tufts University, Medford, Massachusetts 02155
Martin H. Wolf Cambridge Analytical Associates, Inc., 1106 Commonwealth Avenue, Boston, Massachusetts 02215
A chemlkmheecent detector (CD) has been evaluated for the analysis of nitrated polycyclic aromatlc hydrocarbons (nltroPAH) via gas chromatography. The detector responded llnearly to most nltro-PAH from 100 ng to 50 pg uslng the experhnentai conditions described In the text. The selectlve detection of nitro-PAH over other hydrocarbons was compared to the relative selectlvltles of flame ionization detecUon and detection with electron Impact mass spectrometry and negative ion chemlcal ionlzatlon mass spectrometry. Models have been developed that predct the gas chromatographlc behavior of nltro-PAH on SE-52. A gas chromatography/ chemiluminescent detector (NO, specific) revealed that a number of nltro compounds were present in a diesel exhaust partlculate sample. The models were used to tentatively identlfy nHro-PAH in the sample. Compound assignment was confirmed by gas chromatography/negative Ion chemical ionization mass spectrometry and standard addltlon experiments.
Nitrated polycyclic aromatic hydrocarbons (nitro-PAH) have been identified as potent mutagens (1-3) and possible carcinogens (4,5). Since 1977, when the EPA first identified diesel exhaust particulates as mutagenic as determined by the Ames assay, the identification and characterization of nitroPAH in complex mixtures have become areas of important research. Nitro-PAH are thought to be responsible for up to 90% of the total mutagenicity of diesel particulates; one study suggested that 1-nitropyrene alone was responsible for up to 20% of the mutagenic response (6). Pitts et al. (7)first postulated that nitro-PAH were formed as byproducts of postcombustion interactions between PAH and nitrogen oxides. Other researchers have found nitro-PAH in diesel exhaust particulatea (8-lo), gasoline exhaust (5,l l ) ,coal-burning power plants (12),cigarette smoke (12),and air particulate matter (1,13).Atmospheric conversion of PAH to nitro-PAH has also been postulated (14). Concern about the possible environmental and health-related effects of diesel exhaust particulates is of great importance. The small size (less than 10 pm in diameter) of these particulates makes them easily respirable to deeper areas of the lungs. The deeper sections have no cilia or mucus to trap and clear the particles, which may lead to an increased probability of cancer relative to that produced by larger, more easily cleared particles. To date, at least nine nitro-PAH that have been identified in diesel exhaust (1-nitropyrene, 2nitrofluorene, 3-nitrofluoranthane, 2-nitronaphthalene, 4Present address: Cambridge Analytical Associates, Inc., Boston, MA 02215,
nitrobiphenyl, 5-nitroacenaphthene, and 1,3-, 1,6-, and 1,8dinitropyrene) have produced cancer in laboratory animals (4,5). This information has led both the International Agency for Research on Cancer (IARC) and the U S . National Toxicology Program to evaluate the toxicity of nitro-PAH. The presence of nitro-PAH in complex mixtures is often difficult to confirm due to the trace amounts present. Early studies using conventional (packed-column) gas chromatography were plagued by poor resolution and relied on extensive sample preparation techniques to minimize interference problems. Mass spectral analyses also had drawbacks in that individual isomers could not be quantitatively determined. Later analyses have relied almost exclusively on capillary column gas chromatography. Several detectors have been used with varying degrees of success. Several researchers evaluated flame ionization detectors (FID) for the analysis of nitro-PAH. The FID has two major drawbacks: it is insensitive to nitro-PAH relative to other detectors, with detection limits of 0.1-0.2 ng at best, and is also nonselective relative to other detectors. The electron capture detector (ECD) has very good sensitivity to nitroPAH, on the order of 1-2 pg (13). Selectivity is also fairly good, due to the electron affinity of the nitro-PAH. On the other hand, other electronegative species such as oxygenated PAH give strong responses, while the response of the ECD varies by up to a factor of 60 between nitro compounds. Several researchers have found alkali-flame nitrogen-phosphorus detectors (NPD) to have detection limits similar to the FID and a selectivity toward nitrogen compounds in general that is better than the ECD (15, 16). Finally, gas chromatography/electron impact ionization mass spectrometry (GC/EIMS) has been used extensively for the identification of nitro-PAH (9,10,17). The MS provides an abundance of information on the actual structure of the molecule and therefore can allow for tentative identification of a compound when no standard is available. However, it is insensitive (generally in the low nanogram range) and nitro-PAH are often masked by other compounds. Moreover, all of these analyses rely on pre-cleanupof the samples by silica or alumina column chromatography to provide a "nitro" fraction. Negative ion chemical ionization mass spectrometry combined with capillary gas chromatography (GC/NICIMS) has proven to be one of the most selective and sensitive methods for analyzing nitro-PAH. The "soft" ionization of this technique favors electronegative molecules and is similar to the ECD. It also produces a strong molecular ion for nitro-PAH. Oehme et al. (13)have reached detection limits of 100 pg with a full scan and 0.5-4 pg ( S I N = 10) in the single ion monitoring mode for most nitro-PAH. Ramdahl and Urdal (18) established a 1pg ( S I N = 10) detection limit for l-nitro-2methylnaphthalene. The major drawbacks of this technique
0003-2700/86/0358-2078$01.50/00 1986 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 9, AUGUST 1986
2079
are the cost of instrumentation and the lack of reference upectra. We have evaluated a thermionic ionization detector (TID) in a nitrogen atmosphere for the analysis of nitro-PAH (19). Detection limits of 3 pg ( S I N = 3) for 2,2'-dinitrobiphenyl and 9-nitrmthracene were noted, with a linear dynamic range from the detection limit to 110 ng. The sensitivity and selectivity of the TID toward nitro-PAH show promise; however, widely different responses between nitro compounds and the possibility of interferences (other electronegative compounds present in the sample) pose a problem. In another paper (20), multivariate linear relationships between gas chromatographic retention index, I, and molecular connectivity, "'xt,was developed. The relationship was used to predict nitro-PAH retention behavior (on SE-52) for nitro compounds that were not readily available. The regression equation containing the appropriate m ~ descriptors t (where m is the index order and t is the fragment type) was
was produced by any of the compounds. The above-mentioned chromatographicsystem was linear temperature programmed from 35 "C to 305 "C at 10 "C/min. The reaction chamber pressure was maintained at 1 torr. The linear temperature programmed retention indexes of 51 nitro compounds were evaluated under the same chromatographic conditions. The nonresponse of the CD toward PAH required the retention indexes to be calculated from measured retention times generated by chromatographing methylene chloride solutions of the bracketing standards (1-nitronaphthalene, 9-nitrophenanthrene, and 6-nitrochrysene) and the nitro-PAH. These compounds were chosen because they were nitrated analogues of the original bracketing standards (21). The respective retention indexes were generated postrun by use of a computer program on the IBM 9000. The program calculated the retention indexes according to the relationship of Van Den Do01 and Kratz (22)
1 = 135.65lx" + 60.543x - 31.90'~- 124.654xv+ 56.335~v - 33.10'~+ 21.35 (1)
where I is the retention index, tR(Bd-) is the measured retention time of the substance for which the retention index is to be ) tR(n+l)are the measured retention times of determined, t ~ ( "and the bracketing compounds that elute just before and after the compound of interest, and n is the number of rings of the nitro-PAH bracketing standard that elutes prior to the compound of interest. Molecular connectivity, x, is a topological description of molecular structure based on a count of skeletal atom groupings, weighted by the degree of skeletal branching (23). Molecular connectivity indexes have been calculated for nitro-PAH by the method shown in ref 24. The relative selectivity of the detector was determined by analyzing a reference material (Oldsmobile diesel exhaust particulates) supplied by the EPA and a soil sample contaminated with a lubricating oil. The EPA sample (200 mg) was extracted by use of toluene and methylene chloride in an ultrasonic bath. The extract was diluted to 1 mL and separated into several aliquots for analysis by GC/FID, GC/EIMS, and by GC/CD. One aliquot was spiked with EPA recommended internal standards @-dichlorobenzene-d4,naphthalene-d,, acenaphthene-dlo,phenanthrene-dlochrysene-d12and benz[a]pyrene-dI2)before analysis. A Hewlett-Packard 5880 GC was used for the FID comparison by using the same chromatographicconditions as described above. A Hewlett-Packard 5993C GC/MS was tuned to decafluorotriphenylphosphine (DFTPP) using EPA criteria and the sample was analyzed with respect to the same chromatogaphic conditions as described above. Mass range from m/z 40 to 450 was scanned every second and stored in an HP-3000 data system with ANSWER software. The electron multiplier was set at 1800 V. Other aliquots of sample were spiked with different concentrations of several nitro-PAH and analyzed to estimate the detection limit of the nitro-PAH in a complex mixture. The soil sample was prepared by an 8-h Soxhlet extraction (acetone/hexane 5050) and analyzed by GC/FID and GC/CD. Several compounds in the diesel particulate sample were tentatively identified by use of the CD based on the retention index of the detected peak and molecular connectivity algorithms. Confirmation of the compounds was performed on a Finniian 4100 GC/MS with an INCOS data system and an on-column injection system. Negative ion chemical ionization was used with methane as the reagent gas. The mass spectrometer was tuned to perfluorotributylamine (FC-43) before analysis. The electron multiplier was set at 900 V. Prior to analysis, 100 fiL of the sample was evaporated to dryness under a stream of nitrogen and then dissolved in hexane. The solution was carefully added to a hexane-rinsed silica Sep-PAK (Waters Associates). Eight milliliters of hexane was passed through the column and discarded. An 8-mL solution of 50:50 (v/v) hexane/methylene chloride was eluted and collected for analysis by GC/NICIMS. Nitro-PAH were previously found to elute in this fraction.
Validation of eq 1for predicting nitro-PAH retention characteristics was made by comparing actual "'xtvalues for a given compound with their corresponding predicted m ~ estimates. t The predicted "'xt estimates were obtained by use of the corrected inverse regression estimator (eq 4 in ref 20). Agreement of the actual and predicted m ~ values t within 2% indicated that the corresponding I yielded the correct retention behavior for that compound. This paper reports the utility of high-resolution gas chromatography with N02-specific,chemiluminescent detection and the applicability of the above equations (i.e., prediction of I and x) as screening tools for identifying and estimating the concentration of some nitro-PAH in a complex diesel exhaust particulate sample. The linear dynamic range, selectivity, and sensitivity of the CD toward nitro-PAH are reported.
EXPERIMENTAL SECTION A Hewlett-Packard 5790A gas chromatograph equipped with a capillary injector was used for the detector evaluation. The chromatographic conditions are similar to those employed in a previous paper (21). The column was a 25 m X 0.31 mm i.d. fused silica capillary coated with a 0.25-pm film of SE-52, with helium as a carrier gas at 2 mL/min at 25 "C. Graphite ferrules were used for all column connections. The methylene chloride solutions of the standards were introduced by using splitless injection (a 454 splitless period) into a 300 "C injector. The detector was connected to the gas chromatograph by a heated (300 "C) interface supplied by Hewlett-Packard. The pyrolysis chamber consisted of a 1/4 in. 0.d. quartz tube maintained at loo0 "C by a Lindbergh tube furnace. The tube was connected to the interface and the cold trap via stainles steel Swagelok unions and Supeltex M-2A ferrules. The cold trap was a 1/4 in. 0.d. stainless steel tube immersed in a liquid nitrogen/acetone slush bath. The ozone was produced with oxygen and a Thermo Electron Corp. ozonator. Teflon tubing and stainless steel unions were used for all connections. A Thorn-EMI-Gencom Fact-50 MK I11 thermoelectrically cooled housing containing a ThornEMI-Gencom photomultiplier tube (Model9658B) was interfaced to the stainless steel reaction chamber by steel flanges. A red filter was inserted between the housing and reaction chamber flanges and supported by Viton O-rings. The PM tube output was collected by a Keithley instruments Model 600B Electrometer and then sent to an IBM 9000 data system equipped with Chromatography Application Program software. The linear dynamic range of the detector was evaluated with a methylene chloride solution containing five nitro-PAH (2nitronaphthalene, 4-nitrobiphenyl, 1,4-dinitronaphthalene, 9nitrophenanthrene, and 6-nitrochrysene)at 100 ng/& each. The solution was diluted and each dilution was analyzed under the same conditions. This procedure was repeated until no signal
RESULTS AND DISCUSSION The separation of nitro-PAH on the fused silica SE-52 column with chemiluminescent detection is shown in Figure 1. The identification and retention index of each labeled peak
2080
ANALYTICAL CHEMISTRY, VOL. 58, NO. 9, AUGUST 1986
Table I. Retention Index of Nitrated Polycyclic Aromatic Hydrocarbons no.
compound
I
1
5-nitroindan 5-nitro-l,2,3,4-tetrahydronaphthalene 5-nitroquinoline 1-nitronaphthalene 5-nitro-6-methylquinoline 1-nitro-2-methylnaphthalene 2-nitronaphthalene 6-nitroquinoline 2-nitrobiphenyl 8-nitroquinoline 8-nitroquinaldine 8-nitro-7-methylquinoline 3-nitrobiphenyl 4-nitrobiphenyl 4-nitrophenyl phenyl ether 1,4-dinitronaphthalene l&dinitronaphthalene 4-nitroquinoline N-oxide 1,3-dinitronaphthalene 3-nitrodibenzofuran 2-nitrofluorene 3-nitro-9-fluorenone 4-nitrophenanthrene 9-nitroanthracene l&dinitronaphthalene 9-nitrophenanthrene 2-nitro-9-fluorenone 2,4-dinitrophenyl 2-methylphenyl ether 2-nitrophenanthrene 1-methyl-9-nitroanthracene 2,2'-dinitrobibenzyl 3-nitrophenanthrene 2-nitroanthracene 2-methyl-9-nitroanthracene 1-methyl-10-nitroanthracene 9,10-dinitroanthracene 9-methyl-10-nitroanthracene 7-nitro-3,4-benzocoumarin 2-nitrofluoranthene 3-nitrofluoranthene 4-nitropyrene 1-nitropyrene 2-nitropyrene 2,6-dinitro-9-fluorenone 2,5-dinitrofluorene 2,7-dinitro-9-fluorenone 4-nitro-p-terphenyl 1,3,6,8-tetranitronaphthalene 2,4,7-trinitro-g-fluorenone 6-nitrochrysene 1,3-dinitropyrene 1,6-dinitropyrene l&dinitropyrene 2,4,5,7-tetranitro-9-fluorenone
187.52" 197.90a 198.90' 200.00 203.94 205.38 207.30 209.74 217.20 229.31 235.00 236.87 239.64 244.47 248.12 252.26 260.20 263.42 264.68 265.93 284.69 287.74 288.44 289.54 293.54 300.00 300.45 304.33 305.15b 305.23 306.86 307.66 310.01b 311.03b 311.06b 319.07 321.60 333.17 350.17 351.96 354.26 360.78 363.02 363.70 370.05 372.98 377.01 381.70 389.39 400.00 414.29' 422.20a 429.36" 430.77"
2 3 4 5 6 7 8 9 10 11 12 13 14
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
Retention indexes calculated by plotting 37 common nitroPAH in this study and in ref 21. bPredicted retention index (ref 20). is listed in T a b l e I. T h e concentration of each compound ranged from 10 to 50 ng injected. The CD was found t o respond linearly up t o 100 ng, with a detection limit of 50 pg for most compounds at a S I N of 3. Poor separation efficiencies due t o column overloading prevented evaluation of the upper limit of the linear working range. Table I1 displays t h e linear relationship between the response and t h e amount injected for five nitro-PAH. Approximately molar response (333%) was found per nitro group. The decreasing slope with increasing molecular weight, as well as roughly twice t h e signal response of 1,4-dinitronaphthalene t o that of t h e 2-nitronaphthalene, makes this relationship evident. The minimum detectable a m o u n t of each compound is dependent o n t h e molecular weight, the number of nitro
53
1
1
1
35
235
305
T ~ P E R A T U R Eo,c Figure 1. Chromatographic profile of a methylene chloride solution of nitro-PAH using the CD. The numbered chromatographic peaks are identified in Table I. 'I
Table 11. Comparison of Linear Response and Relative Molar Response of Five Nitro-PAH compd
mole fract
slope
inter
corr
RMR"
7 14 26 50 16
0.266 0.231 0.206 0.168 0.422
2.68 2.37 1.88 1.42 4.57
-0.67 -0.73 -11.56 -0.30 -0.20
0.9999 0.9999 0.9966 0.9998 0.9999
1.00 1.02 0.91 0.84 1.07
The RMR (relative molar response) is based on the ratio of the slope and the mole fraction for each compound relative to the ratio 2-nitronaphthalene ( 4 ) . Compounds are identified in Table I. groups on the molecule, a n d the chromatographic system and detector. The CD works in t h e following manner. After separation in the GC, the nitro-PAH enter a pyrolysis chamber a t lo00 "C and decompose to form nitrosyl radicals (NO.) and other products. The products are drawn by vacuum into a cold t r a p where most of the remaining fragments are frozen out. T h e NO- continues o n to a reaction chamber under reduced pressure where i t reacts with ozone to produce a characteristic infrared chemiluminescence. T h e process is highly selective due t o t h e characteristics of the cold trap, photomultiplier tube, and a red filter employed i n these analyses. T h e detector response is a function of t h e ozone flow rate, reaction chamber pressure, the PM tube response, and t h e pyrolysis temperature. Each of these variables can change t h e final response of the detector. T h e pyrolysis temperature affects t h e CD response (i.e., dynamic range) of each compound particularly at lower temperatures. A t temperatures less t h a n 500 "C there is little or n o conversion of the nitro group t o t h e nitrosyl radical, while at temperatures greater t h a n 1000 "C n o significant increase in response is noted. T h e optimum temperature for conversion was found
ANALMICAL CHEMISTRY, VOL. 58, NO. 9, AUGUST 1986
0
L
5
72
TIME
.:3
7j
??j
755
1s
20
2r
2081
2a
(rnin) 105
275
305
TEMPERATURE 2?oC'c)
Chromatographic profile of diesel exhaust particulate extract using the FID. The labeled peaks are EPA internal standard compounds: (1) p dichlorobenzene-d,, (2) naphthalensd,, (3)acenaphthene-d,,, (4) phenanthrene-d,,, (5) chrysene-d,,, (6) benzo[a Ipyrene-d,,. Figure 2.
r
-
1
J
Figure 3. Chromatographic profile of a soil extract contaminated with a lubricating oil. This sample was spiked with the same EPA bracketing
standards as Figure 2 and analyzed under the same conditions.
to be 950-1000 "C. A full discussion of the detector theory may be found elsewhere (25). Figures 2 and 3 show GC/FID chromatograms of the Olds diesel particulate extract and the extract of a soil contaminated with a lubricating oil; approximately 200 Wg was injected,
--
:;
'ij
1"s
4:
iZ5-
27:
3Cj
T E M P ~ R ~ R( E 2 Figure 4. Chromatographic profile of the same diesel exhaust particulate extract (Figure 2) but by CD. Three of the labeled peaks (4, 26, 50) are nitro-bracketingcompounds at 16 ng injected. The other numbered peaks are compounds detected in the extract.
respectively. A GC/EIMS total ion chromatogram for the same Olds extract was similar to that generated by the FID. Due to the complexity of the sample, no nitro-PAH were readily observable in the Olds extract by FID, and only 1nitropyrene by GC/EIMS. Diesel particulate and lubricating oil extracts spiked at an additional 100 ng (injected) of each nitro-PAH were required before visible nitro-PAH peaks could be detected by FID. The universal response of the FID severely limits ita usefulness as an analytical tool for the analysis of nitro-PAH. On the other hand, nitro-PAH were detected by GC/EIMS when 10 ng of each compound was spiked into the sample, based on the presence of the molecular ion and retention index. However, absolute confirmation based on the presence of major fragments (m/z M - 30, loss of N O m / i M - 45, loss of NOz) was not possible until higher concentrations were added. The universality of the EIMS toward organic molecules prohibited identification of nitro-PAH without sample cleanup or single-ion monitoring since nitro-PAH are easily masked by the parent PAH and alkyl or oxygenated derivatives of the PAH. Figure 4 shows the chroinatographic profile CD signal response of the Olds extract. For comparison, Figure 5 illustrates the chromatographic profile by GC/CD of the same lubricating oil extract shown in Figure 3, but by GC/CD. The detector settings are the same as those for the Olds dies84 bxtract chromatogram. The only identifiable peaks are the three bracketing standards at 8 ng injected each. At no detector settings were nitro-PAH observable. The selectivity of the CD is readily apparent. The highly complex mixture signal response in the diesel extract is thought to be from the many possible isomers of nitro-PAH present at trace quantities. Labeled in Figure 4
2082
ANALYTICAL CHEMISTRY, VOL. 58, NO. 9, AUGUST 1986 I
Table IV. Predicted x Values for ID ID
T
0
-
7-
~
;2
6
4
7
TIME
21
20
26
(min) 1
55
75
115
155
'7~ 275
TEMPERA~ZRE
3Cj
Figure 5. Chromatographic profile of the same lubricating oil extract (Figure 3) by CD. The only identifiable peaks are the three bracketing compounUs at 8 ng injected.
best match(es) I
a
b
284.77 287.84
284.69 287.74 288.44 289.54 288.44 289.54 300.00 300.45 305.15 305.23 305.15 305.23 307.66 307.66 310.01 310.01 311.03 311.06 350.17 351.96 360.78 363.02 400.00
6 5 1 1 6 7 7 2 3 3 0 4 0 5 4 2 3 4 7 7 7 7 7
7 7 4 4 7 7 7 4 5 5 0 6 0 7 6 6 7 6 7 7 7 7 7
289.89 300.00 304.61 306.40 308.47 310.26 351.98 361.56 400.00
X
3.958 3.856 3.923 3.862 4.402 3.825 4.495 4.204 3.883 4.472 3.927 4.677 4.693 5.075
0
x
1x
11.303 7.813 11.856 8.179 11.785 8.249 11.870 8.280 12.410 8.580 11.954 8.253 12.487 8.643 12.224 8.476 11.958 8.310 12.519 8.655 12.011 8.359 13.055 9.274 13.110 9.280 14.270 10.351
2x
3x
7.217 7.569 7.470 7.484 7.927 7.583 7.977 7.781 7.579 7.980 7.632 8.601 8.701 9.067
6.181 6.609 6.310 6.400 6.705 6.577 6.721 6.608 6.520 6.766 6.581 7.735 7.797 8.241
Alkylated-nitro-PAHbrackets used to obtain correction vector.
Table V. Comparison of Standard Addition, I,,, and I N O I Values compound
2-nitrofluorene 9-nitroanthracene
ISA
285.34 289.88 1-methyl-9-nitroanthracene 304.78 1-methyl-9-nitroanthracene 304.75 1-methyl-10-nitroanthracene 310.43 3-nitrofluoranthene 352.22 1-nitropyrene 361.81
Number of predicted x values agreeing within 1%of actual x values. 'Number of predicted x values agreeing within 2% of actual x values.
are the nitrated-PAH bracketing standards and diesel indexes, present in the extract. Table I11 lists the ID values shown in the figure and the correspohding I best match(es). Experimentally determined and predicted retention indexes and corresponding actual m ~ descriptor t values have been determined for all mononitrated naphthalene, fluorene, phenanthrene, anthracene, and most of the fluoranthene isomers, as well as some alkylated mononitroPAH (20). All nitro-PAH eluting within f 2 index units of ID are considered candidate compounds. The identity of the I best match(es) are given in Table I. For each ID, seven n ~ estimates (viz., Oxv, lxV,2xv,Ox, 'x,2x,and 3x)are computed based on eq 4 in ref 20, as shown in Table IV. Columns A and B (Table 111) indicate how many of the seven n ~estit mates predicted were within 1 and 2%, respectively, of the actual x values for each candidate compound. Prior to the addition of 1-nitronaphthalene, 9-nitrophenanthrene, and 6-nitrochrysene, GC/CD chromatograms of the diesel particulate extract revealed the absence of peaks within 110 s of the elution time (correspondingto *2.6 index units) of the standards in pure methylene chloride solution.
2 v
* Nitro-PAH brackets used to obtain correction vector.
Table 111. Candidate Nitro-PAH in of the Diesel Exhaust Particulate Extract ID
lX"
284.77 8.578 5.092 287.94 8.776 5.119 289.89 8.947 5.333 300.00 8.991 5.302 304.61" 9.611 5.694 304.61' 8.927 5.171 306.40'' 9.744 5.794 306.40' 9.404 5.552 308.47 9.044 5.288 310.26" 9.760 5.782 310.26' 9.092 5.331 351.98 9.999 6.060 361.56 10.014 6.017 400.00 11.214 6.885
r
-1-
16
OXY
ID, for suspected nitro-PAH
t
ID
concn, a l p
284.77 289.89 304.61 306.40 310.26 351.98 361.56
10 35 10 30 12 10 100
In fact when these compounds are added to the diesel sample, three new peaks appear. The addition of the standards into the diesel sample illustrates the applicability of the predictive equations for tentative compound identification. Table 111 indicates the better match of 9-nitrophenanthrene relative to 2-nitro-9-fluorenoneat ID = 300.00, since all of the predicted m ~ estimates t are within 2% of the actual values. Standard addition experiments of 9-nitrophenanthrene resulted in an increase in GC/CD response as expected. GC/CD chromatograms further illustrated the absence of peaks within 35 s of the Snitrochrysene standard. Based on the comparison of actual and predicted x's, we assign 6-nitrochrysene as the compound eluting at ID = 400.00. The excellent comparison between actual and predicted "'xt estimates (average of 1%difference) for the 32 mononitroPAH standards (20) and the excellent agreement reported above for compounds eluting in a complex sample matrix, such as the diesel exhaust particulate extract, suggested that the criteria for tentative compound identification be a difference of 1 2 % between actual and predicted "'xtvalues. GC/CD, GC/NICIMS, and standard addition experiments were made when applicable for confirmation of compound identity (Table VI. Comparison of actual and predicted n ~values t suggested 2-nitrofluorene at ID = 284.77. Addition of this compound resulted in an increase in GC/CD response. Three compounds, 3-nitro-9-fluorenone, 4-nitrophenanthrene, and 9-nitroanthracene had indexes similar to ID = 287.84. Table I11 indicates a mismatch for the latter two compounds. GC/MS confirmed, at ID = 287.84, the absence of any phenanthrenes or anthracenes and the presence of a mononitrofluorenone. The predictive x model identified which isomer of mononitrofluorenone ID corresponded to. GC/MS of the diesel sample revealed that the molecular ion at 289.89 corresponded to either a mononitrated phenanthrene or anthracene. The best match according to the comparison of actual and predicted x's resulted in candidate compounds of 4-nitrophenanthrene and 9-nitroanthracene. Addition of the latter yielded an increase in the GC/CD signal
ANALYTICAL CHEMISTRY, VOL. 58, NO. 9, AUGUST 1988
response ( I S A = 289.88). Addition of the former produced a new GC/CD peak signal eluting prior to 289.89. Although the predictive x model was unable to differentiate these two compounds, it did narrow the candidate list from a total of eight mononitrated phenanthrenes and anthracenes. The peak a t ID = 304.61 corresponded to either 2-nitrophenanthrene or 1-methyl-9-nitroanthracenebased on their reapective I values. The model, however, indicatea that neither compound best matches the predicted "'xta t this retention index. GC/MS data corresponding to this elution time indicated the presence of a mononitrophenanthrene or anthracene containing a methyl group. Addition of l-methyl9-nitroanthracene produced an increase in the GC/CD signal (Im=. 304.78) as one would expect based only on I information. At ths point, no compound is assigned to this peak since the number of methylmononitroanthracenes and phenanthrenes that may have similar retention behavior has not been evaluated. On the other hand, since the NOz chemiluminescent detector is molar-responding, an estimation of the compound concentration is measured and shown in Table V. The actual "'xtvalues for 2- and 3-nitrophenanthrene poorly match the predicted "'xtestimates calculated at I D = 306.40. This is confirmed by GC/MS denoting the presence of another methylmononitroanthracene or phenanthrene. On the basis of the standard addition experiment above, compound concentration a t this retention index is measured and reported in Table V. Again, we are limited by the number of alkylated nitro-PAH isomers needed to be synthesized and evaluated. GC/MS at ID = 308.47 indicated either nitrophenanthrene or nitroanthracene isomers. Comparison of relevant '"xt's reduced the number of candidate isomers from eight to two. Three candidate compounds elute within f l index unit of ID = 310.26. GC/MS data corresponding to this retention time indicated the presence of a methylmononitroanthracene or phenanthrene, eliminating I = 310.01. Addition of 1methyl-10-nitroanthraceneresulted in a GC/CD peak a t I S A = 310.43. Based on the spiking experiment, one might assign this compound to the peak. The model on the other hand, suggested an equally likely isomer of methylnitroanthracene having the same retention characteristics. On the basis of Table 111,3-methyl-9-nitroanthracene may be a more likely candidate. Retention data corresponds to mononitrofluoranthenesand pyrenes at I D = 351.98 and 361.56, respectively. This is consistent with GC/MS results; i.e., no alkylated isomers of these compounds were observed. Standard additions of 3nitrofluoranthene and 1-nitropyrene increased the GC/CD peak signals at I s A = 352.22 and 361.81, respectively. Clearly, the large differences in I values for each set of compounds at a given I confirms the identity of the peak. Table V indicates the relative concentrations of the nitroPAH present in the sample before standard additions as determined by GC/CD. Compounds identified by GC/NICIMS were made after sample cleanup through a silica column. The presence of hydrocarbons, PAH, and oxygenated PAH such as aldehydes, ketones, and carboxylic acids masked even semiselective NICIMS response of nitro-PAH, necessitating sample preparation before confirmation could be made. The major contribution of these models, viz., the ability to predict retention characteristics of mononitrated PAH for compounds where no experimental data exists and validation of the predicted I by comparing actual x values with predicted x estimates (201,allows the analyst to look for specific isomeric nitro-PAH in the sample. Further, the models in most cases limit the large number of potential isomers to a few. Comparison of actual and predicted x's reduced the number of candidate compounds based on retention index and mass spectrometry considerations. Moreover, if a complete list of
2083
s'l for alkylated isomers of nitro-PAH were easily obtainable, comparison of "'xt values should lead to a minimum list of candidate compounds for experimental determination and confiation. The use of the models in combination with the excellent selectivity and sensitivity of the gas chromatographic chemiluminescent detector serves as a useful screening tool for the analysis of nitro-PAH in complex mixtures. Because the detector is molar-responding, one can estimate the concentration of nitro-PAH in the sample. This is of particular interest due to the large number of isomeric nitro-PAH and alkylated nitro-PAH compounds having between two and four condensed rings present in diesel samples, and the environmental concern because of the high mutagenic and carcinogenic activity of some nitro-PAH.
ACKNOWLEDGMENT The authors wish to thank Cambridge Analytical Associate, Inc., for the use of the mass spectrometers and for technical support, John Haas (Gordon College), Curt White (US. Department of Energy, PETC), Dennis Schuetzle (Ford Motor Co.), and Milton Lee (Brigham Young University) for the many helpful discussions, and Silvester Tejada (EPA) for the diesel exhaust sample. Registry No. 5-Nitroindan,7436-07-9;B-nitro-1,2,3,4-tetrahydronaphthalene, 29809-14-1; 5-nitroquinoline, 607-34-1; 1nitronaphthalene, 86-57-7; 5-nitro-6-methylquinoline, 23141-61-9; l-nitro-2-methylnaphthalene,881-03-8; 2-nitronaphthalene, 581-89-5; 6-nitroquinoline, 613-50-3; 2-nitrobiphenyl, 86-00-0; 8-nitroquinoline,607-35-2; 8-nitroquinaldine, 881-07-2;8-nitro7-methylquinoline, 7471-63-8; 3-nitrobiphenyl, 2113-58-8; 4nitrobiphenyl, 92-93-3;4-nitrobiphenyl phenyl ether, 620-88-2; 1,4-dinitronaphthalene,6921-26-2;4-nitrcquinoliie oxide, 56-57-5; 1,3-dinitronaphthalene,606-37-1; 3-nitrodibenzofuran,5410-97-9; 2-nitrofluorene, 607-57-8; 3-nitro-g-fluorenone,42135-22-8; 4nitrophenanthrene, 82064-15-1; 9-nitroanthracene, 602-60-8; l,&dinitronaphthalene,602-38-0; 9-nitrophenanthrene, 954-46-1; 2-nitro-%fluorenone,3096-52-4;2,4-dinitrophenyl2-methylphenyl ether, 2363-26-0;2-nitrophenanthrene,17024-18-9;l-methyl-9nitroanthracene, 86695-76-3; 2,2'-dinitrobibenzyl, 16968-19-7; 3-nitrophenanthrene,17024-19-0;2-nitroanthracene,3586-69-4; 2-methyl-9-nitroanthracene, 102630-62-6; 1-methyl-10-nitroanthracene, 86689-95-4; g,lO-dinitroanthracene, 33685-60-8;9methyl-l0-nitroantlracene,84457-22-7;7-nitro-3,4-bem&, 22371-68-2;2-nitrofluoranthene,13177-29-2;3-nitrofluoranthene, 892-21-7; 4-nitropyrene, 57835-92-4; 1-nitropyrene, 5522-43-0; 2-nitropyrene, 789-07-1; 2,6-dinitro-9-fluorenone,58160-30-8; 315512,5-dinitrofluorene, 15110-74-4;2,7-dinitro-9-fluorenone, 45-8; 4-nitro-p-terphenyl, 10355-53-0; 1,3,6,8-tetranitro129-79-3; naphthalene, 28995-89-3; 2,4,7-trinitro-g-fluorenone, 6-nitrochrysene, 7496-02-8; 1,3-dinitropyrene, 75321-20-9; 1,6dinitropyrene, 42397-64-8; l&dinitropyrene, 42397-65-9; 2,4,5,7-tetranitro-9-fluorenone, 746-53-2. LITERATURE CITED (1) Wang, Y. Y.; Rappaport, S. M.; Sawyer, R. F.; Talcott, R. E.; Wel, E. T. Cancer Lett. 1978. 5 , 39-47. (2) Salmeen, I.; Durlsln, A. M.; Prater, T. J.; Riley, T.; Schuetzle, D. Mutat. Res. 1982, 104, 17-23. (3) Rosenkranz, H. S. Mutat. Res. 1982, 101, 1-10. (4) Wel, E. T.; Shu, H. P. Am. J . Public Health 1988, 79, 1085-1088. (5) Rosenkranz, H. S. Mutat. Res. 1984, 140, 1-6. (6) PMs, J.; Lokensgard, D.; Harger, W.; Fisher, T.; Mejia, V.; Schuler, J.; Schorzlella, G.; Katzensteln, Y. Mutat. Res. 1982, 103, 241-249. (7) Pma, J. N., Jr.; Van Cauwenberghe, K. A.; Grosjean, D.; Schmid, J. P.; Fltz. D. R.; Belser. W. L., Jr.; Knudson. G. B.: Hvnds, P. M. Science 1978, 202, 515-519. (8) Scheutzle, D.; Lee. F. S.C.; Prater, T.; Tejada. S. Proceedlngs of bk, 10th Annual Symposium on the Anal)rticel Chemlstry of Pollutants; Gordon and Breach Sclence Publlshers: New York, 1980 pp 193-244. (9) Schuetzle, D.; Papute-Peck, M. C.; Marano, R. S.; Riley, T. L.; Hampton, C. V.; Prater, T. J.; Skewes. L. M.; Jensen. T. E.; Ruehle, P. H.; Bosch, L. C.; Duncan, W. P. Anal. Chem. 1988, 55, 1946-1954. (10) Newton, D. L.; Erlckson, M. D.; Torner, K. B.; Pelllzarl, E. D.; Gentry, P.; ZweMlnger, R. B. Envkon. Scl. Technol. 1982. 16, 206-213. (11) Alsberg, T.; Stenberg, U.; Westerholm, R.; Strandel, M.; Rannug, U.; Sundvall, A.; Romert, L.; Bernson. V.; Peltersson, B.; Toftgard. R.; Franzen, B.; Jansson, M.; Gustafsson, J. A.; Egebak, K. E.; Tejle. G. Envlron. Sci. Technol. 1985, 19, 43-50.
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Anal. Chem. 1986, 58,2084-2087
(12) WMe, C. M. I n Nlbnbed W y W Arometb Hydrocanbons;White, C. M., Ed.; R. Alfred Hmlhig Verlag: Heidelberg, 1985. (13) Cehme, M.; Mano, S.; Stray, H. H1(: CC,J . M@I R e d u t . ChromefOgr. Chrometogr. Conwnun. 1982, 5 , 417-423. (14) PMs, J. N., Jr. Phlbs. Tr8ns. R . SOC. London, A 197%. 290, 551-576. (15) Llberti, A.; Ckcloli, P.; Ceclnato. A.; Brancaleonl, E.; Malo, C. M C CC, J . H&h Resolut. C h r m t o g r . Chromatogr. Commun. 1984, 7 , 389-397. (16) Ramdahl, T.; Kveseth, K.; W,Q. kRC CC, J . H&h ResoM. Chrome&@. Chrometogr. COtTWnM. 1982, 5 , 19-26. (17) Mes, R. A.; Yu, M.; Thll)y, W. Q. I n Po&wc/ear AromeNc W o carbons; Cooke, M., Dennis, A. J., Eds.; Battek Press: Columbus, OH. 1981; pp 455-466. (18) RamdeM, T.; Urdal. K. Anel. Chem. 1982, 54, 2256-2260. (19) White. C. M.; Robbat, A., Jr.; Hoes, R. M. Anel. Chem. 1984. 56, 232-236. (20) Robbat, A., Jr.; Cocso. N. P.; Doherty, P. J.; Marshall, D. And. Chefn., preceding paper In this Issue.
(21) white, C. M.; Robbat, A., Jr.: Hoes, R. M. ChrometOgrepMe 1983, 17, 605-612. (22) Van Den -1, H.; Kratz, P. D. J . ChKKnetogr. 1963. 7 7 . 463-471. (23) Kier, L. B.; Hall. L. H. Mdeculer Connectivky In Chem/stry and Drug Research; Academic Press: 'New York, 1976. (24) Robbat, A., Jr.; Doherty, P. J.; Hoes, R. M.; Whke, C. M. Anal. Chem. 1984. 56, 2697-2701. (25) Doherty, P. J. M.S. Thesls, Chemlstry, Tufts Unhrerslty, Medford, MA, 1985.
RECWEDfor review October 3,1985. Accepted April 17,1986. The donors of the Petroleum Research Fund, administered by the American Chemical Society, partially supported this research, based in part on a Ph.D. Thesis by Nicholas P. Corso and M.S. Thesis by Philip J. Doherty.
Solution Nebulization into a Low-Power Argon Microwave-Induced Plasma for Atomic Emission Spectrometry: Study of Synthetic Ocean Water Kin C. Ng* and Wei-lung Shen
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Department of Chemistry, California State University-Fresno, Fresno, California 93740
A MAK nebulizer k w.d to introduce liquid aeC000k condevelopment of the Beenakker cavity (4-8), liquid aerosol now can be directly introduced into this atmospheric pressure tahlng Cr, In, V, W, &, or t Mo a kwgoumr (105-115 discharge. Several gases (nitrogen, argon, air, and helium) W), low wgon Ikw (537 mVmln) mkrowavdwhcod pbma can be used as the plasma support gas. Owing to the attractive for atomlc .mkdonspectrometry. Mectlon ilmik ( 3 4 in (low power and low gas consumption rate and the 3% n M c a d d w a t e r ~ s r o a t t h e ~ ~ l e v efeatures l ability of the Beenakker system to efficiently couple micro(82, 18, 18, 91, 139, 13, and 3945, r.+pectively). There wave power) of the MIP, researchers have recently renewed valws compared favorcibty to thore r0poti.d for a 150-W interests in the MIP, in particular to investigate its performAr-MIP and the mvwMonai includlvdy co@od p h m a for ance for directly introduced liquids. Success of this direct most ot the eioments. I n a 10% rynuHtk ocean water sample introduction may make the MIP competitive with the m r r t r b q r i q u l ~ b o M . l r m l t o r C r , M n In,W,and , ICP as a spectroscopic excitation source. Several workers have Sr, and &lgnai depreadon le found for V and Zr. Detection reported direct liquid aerosol introduction into the MIP limits (parts p r arrOn) in tho 10% ocean water are 9, 3, 8, sustained in the Beenakker cavity: Beenakker et al. (4-8) have 1780, 54, 2, and not mecwwabk, for Cr, Mn, In, V, W, Sr, reported a 150-W, 1.2 L/min argon flow MIP; Haas and Caa n d t , r e @ p d d y . "h684pdpndrknirtrplcdly2%RSD ruso (9)have used a 510-w, 450 mL/min argon MIP; Mifor 1 ppm soiutkm. Linoar reqmses (>3 orders of magchlewicz and Carnahan (IO)have used a 500-W, 17.5 L/min nitude) are arr0dst.d W#I all of the te8ted analyte concenhelium MIP for chloride determinations; Urh and Carnahan trations of water or synthetic ocean matrices. (11)have investigated a 300-500-W, 2.9-8.64 L/min air ME';
Plasma emission spectrometry has become popular as a multielement analysis technique. The most succeaaful plasma is the inductively coupled plasma (ICP). Unfortunately, the high-power (>0.7 kW), high argon consumption rate (>12 L/min) ICP instrument is expensive both to purchase and to operate. To reduce such costs, many workers have attempted to miniaturize the ICP so that lower powers and gas consumption rates could be used. Hieftje (I) has reviewed mini and micro ICP's. The microwave-induced plasma (MIP) is another useful plasma source. The low-power (
