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Anal. Chem. 1084, 56, 1820-1826
New Solid-Sorbent Method for Ambient Nitrogen Dioxide Monitoring Frank Lipari Environmental Science Department, General Motors Research Laboratories, Warren, Michigan 48090
A new amblent NO, sorbent method was developed based on quantitative collectlon of NO, in a cartridge contalnlng Florlsil coated wlth dlphenylamlne (DPA). The NO, reacts wlth DPA to form 4-nltro-, 2-nltro-, and N-nltroso-DPA derlvatlves. The NOP products are eluted from the cartrldge, analyzed by hlgh-performance liquid chromatography with UV detectlon, and related to the amount of NO, In the sampled alr. This novel approach utlllzes commerclally available Thermosorb/F air sampling cartridges packed wlth Florlsll as the sorbent. No interferences from NO, Os, HNO,, SO,, and humldlty were found, but PAN produced a 50% posltlve Interference In the method. The detection llmlt is 0.1 ppb NO2 for a 2000-L alr sample which corresponds to an 8-h sampling period at 4.0 L/mln. The cartridges were used to monitor daily ambient NO2 levels ranglng from 1.8 to 33.5 ppb NO, and Indoor NO, levels ranglng from 2.0 to 144.8 ppb NOP.
+
Nitrogen oxides (NO, = NO NO2) are an important class of nitrogeneous air pollutants which play a role in photochemical smog production and acid deposition chemistry (1-3). Most of the NO, emitted by combustion sources is NO which is subsequently oxidized in the atmosphere to NOz. Nitrogen dioxide affects smog chemistry by influencing the photochemical production of ozone and hydroxyl (OH) radicals and by reacting with organic radicals to form peroxyacetyl nitrate (PAN) which is a strong eye irritant (2-5). NOz can also be oxidized to HN03 which is a component of acid precipitation (4-7). Presently, the National Ambient Air Quality Standard for NO2 is 53 ppb (annual average) and as such NO2 is routinely measured in air quality studies. The most commonly used method to measure ambient NO, concentrations is the chemiluminescent method based on the gas-phase reaction of NO and O3 (8-20). The method is specific for NO and is used to measure NOz by catalytically reducing NOz to NO prior to reaction with O3 (11). However, other nitrogeneous species such as HN03 and PAN may also be reduced to NO and interfere with ambient NO2 measurements (12). Recently, another chemiluminescent method based on the reaction of luminol with NOz was reported (13,14).However, this method was still subject to a PAN interference. Other spectroscopic methods developed and utilized for ambient NO2 monitoring include: photoacoustic spectroscopy (15);long path differential optical absorption spectroscopy (16);and Fourier transform infrared spectroscopy with tunable diode lasers (17, 18).
Most commercial NO, instruments have sensitivities for NO and NO2of a few parts per billion (ppb) by volume while some of the more costly and elaborate research spectroscopic techniques have sensitivities for NO and NOz as low as 20 parts per trillion (pptr) by volume (19). The routine use of such complex instruments in the field presents several logistical problems and requires a considerable amount of time and expense for the maintenance and calibration of these instruments in the field. These methods produce real time 0003-2700/84/0356-1820$01.50/0
NO2 readings which in many cases must be integrated over a suitable time period to obtain an average NOz concentration. Therefore, in applications where one needs daily averages or integrated NO2 concentrations, there exists a need for a low cost, simple, and sensitive method for ambient NO2 analysis. Aside from instrumental methods, the classical method for NOz determination is the Griess-Saltzman (20) method in which NOz is absorbed in a sulfanilic acid solution and then coupled with an azo dye forming reagent and measured colorimetrically at 540 nm. Modifications of this method by Jacobs et al. (21)and Levaggi et al. (22) involve trapping NO2 in aqueous NaOH or triethanolamine solutions, respectively, and determining the nitrite formed with Saltzman’s reagent. Presently, commercial NO2 personal samplers developed by Palmes et al. (23, 24) utilize the triethanolamine trapping concept. However, these methods are not widely used because of their limited sensitivity for low-level ambient NOz monitoring. It is well-known that nitrosamines are formed when secondary amines react with nitrogen oxides (25-28).Rounbehler et al. (29,30),in testing air sampling sorbents for nitrosamine collection, found that surface bound secondary amines formed artifact or in situ nitrosamines when exposed to air containing nitrogen oxides. Rounbehler also discovered that weakly basic amines formed greater amounts of nitrosamines than strongly basic amines. This finding implied that a weakly basic amine such as diphenylamine (pK, = 0.79) should react quantitatively with nitrogen oxides to form the N-nitrosodiphenylamine derivative. Fortunately, N-nitrosodiphenylamineis not a carcinogen (31) and as such this concept can be used to determine NOz. Recently, Harrington et al. (32, 33) also utilized diphenylamine to determine nitrite in aqueous solutions by differential pulse polarography. This paper reports on a new method for ambient NO2 sampling and analysis in which NOz is quantitatively collected in a cartridge containing Florisil coated with diphenylamine. The diphenylamine (DPA) reacts with the NO2 in the air to form in situ N-nitroso-DPA (N-NO-DPA), 4-nitro-DPA (4NOZ-DPA),and 2-nitro-DPA (2-N02-DPA)as shown
”
NO
u
NO.
H
The products are eluted and analyzed by high-performance liquid chromatography (HPLC) with the total concentration of all the NOZ-DPAproducts being directly related to the NOz concentration in the air. This report presents the details of the procedure, including collection efficiency, interference, and detection limit studies. The method was used to measure ambient NOz levels in Warren, MI. EXPERIMENTAL SECTION Apparatus. The HPLC system used consisted of a Varian Model-5060 liquid chromatograph with a Vista 401 data station (Varian Associates, Palo Alto, CA), a Perkin-Elmer Model LC-85 (Perkin-Elmer Corp., Norwalk, CT) variable-wavelength UVvisable absorbance detector with a 2.4-kL flow cell, and a Valco (Valco Instruments, Houston, TX) air-actuated injection valve with a 25-kL sample loop. The analytical column used was a 4.6 mm X 25 cm Zorbax-ODS (Du Pont Instruments, Wilmington, 0 1984 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 56, NO. 11, SEPTEMBER 1984
DE) reverse-phase column with a Rainin (Rainin Instrument Co., Woburn, MA) 0.5-pm prefilter. Air sampling was performed with Gilian Model HFS 113 UT (Gilian Instrument Corp., Wayne, NJ) portable constant flow sampling pumps. These pumps are capable of maintaining a constant flow of 1.0 to 4.0 L/min for a 16.5-h sampling period. For field studies, air sampling was done with VWR Model 4K Dynapumps (VWR Scientific, Detroit, MI) and the total gas volumes were measured with a Precision Scientific Model 63125 (VWR Scientific) wet-test meter. Gas flows for the calibration and dilution gases used were measured and controlled with Tylan mass flow controllers (Tylan Corp., Carson, CA). Relative humidities and temperatures were measured with an EG&G Model 880 dew point hygrometer (Princeton Applied Research, Princeton, NJ) and a Keithley Model 871 digital thermometer (Keithley Instruments, Cleveland, OH), respectively. A Sage Model 341A (Orion Research, Cambridge, MA) syringe pump flowing at 0.67 mL/min was used to elute the NOz cartridges. Reagents. HPLC grade solvents obtained from J. T. Baker Chemical Co. (Phillipsburg,NJ) were used to prepare the mobile phase and elute the NOz cartridges. Diphenylamine, Nnitrosodiphenylamine, 4-nitrosodiphenylamine, 4-nitrodiphenylamine, and 2-nitrodiphenylamine were purchased from Aldrich Chemical Co. (Milwaukee, WI) and used as received. Cartridge Preparation. Thermosorb air sampling cartridges packed with high-purity 60/80 mesh Florid (magnesium silicate, Floridian Co.) were used in this study. These cartridges were purchased from Thermo Electron Corp. (Waltham, MA) and are similar to the Thermosorb/N air sampling cartridges used for airborne nitrosamine sampling. The cartridges are constructed of polyethylene and are about 1.5 cm X 2.0 cm long. They have a 100 mesh stainless steel screen at the inlet and a glass wool plug at the outlet to hold in the sorbent. They also have standard Luer-lok fittings at both the inlet and outlet to facilitate sorbent coating and sample elution. The cartridges contain about 1.2 g of dry sorbent. The sorbent is coated with diphenylamine by filling the cartridge with about 2 mL of a 4 mg/mL diphenylamine solution in CHZClz.The cartridges are capped and allowed to stand for 1-2 h. The outlet cap is then removed and the cartridges are placed in a vacuum oven with no heat at 15-20 in. of Hg for about 1 h to volatilize the CHzClzsolvent. The cartridges are then capped and stored and are ready for use. The sorbent retains about 50% of the original amount of diphenylamine placed in the cartridge. This corresponds to about 24 pmol or 4 mg of DPA in each cartridge. This number was determined by eluting a series of cartridges and analyzing the amount of DPA in each cartridge with a diphenylaminestandard solution. Ordinarily, this is more than enough DPA for most applications. Higher loadings of DPA can be coated on the cartridge by increasing the concentration of the diphenylamine coating solution. Generation of Standard NOz Atmospheres. A Metronics (VICI Metronics, Santa Clara, CA) certified NOzpermeation wafer device along with a Metronics Model 350 dynacalibrator permeation system was used to generate known atmospheres of NO2 The permeation rate of the wafer device was determined by bubbling the NO2 gas produced by the permeation system through an aqueous solution of triethanolamine and analyzing the subsequent nitrite produced with Saltzman's reagent (20). The permeation rate was also determined by monitoring the weight loss of the device with a Cahn 100 recording electrobalance (Cahn Instruments, Cerritos, CA) over a 1-weekperiod. The permeation rates determined by these two methods were 82 and 85 ng/min, respectively, which agreed well with the Metronics certified value of 88 h 5 ng/min at 30 "C. The average of these numbers gives a permeation rate of 85 ng/min at 30 "C which was equivalent to 44 ppb NOz/(L min) under our conditions. Higher concentrations of NOz were obtained from NOz Calibration gas cylinders purchased from Scott Specialty Gases (Troy, MI). Sample Elution. The cartridges were backflushed with methanol to elute the NOz-DPA products. After the eluate was collected, 50 pL of 1 N HC1 catalyst was added to the collection vial for each milliliter of eluate collected. The eluate was then
1821
centrifuged for 1 min to settle any sorbent from the collection vial. The sample was then ready for HPLC analysis. Generally, 1-2 mL of methanol was required to quantitatively elute all the NOZ-DPAproducts. However, if the expected amount of NOz collected in a sampling period was low (40 ppb) either from the permeation system or from ambient air. For example, Figure 5 shows two unknown peaks that were observed in the chromatogram corresponding to retention times at 5.7 and 7.4 min. Stopped-flowW scanning of these eluant peaks revealed intense UV absorptions in the
4
I
I
I
I
2
4
6 Time h n )
8
u I
10
12
Chromatogram obtained for a 2000-L air sample of an 11
ppb NO2 mixture from the permeation system, sensitivity 0.04 AUFS: (1) 4-nitro-DPA, (2) N-nitroso-DPA, (3)DPA, (4) 2-nitro-DPA.
380-420 nm range which were indicative of aromatic nitro compounds. Subsequent analysis of these peaks by gas chromatograpy/mass spectroscopy revealed that the 5.7-min peak was 4,4'-dinitro-DPA and the 7.4-min peak was 2,4'dinitro-DPA. Since no commercial dinitro-DPA standards were available, quantitation was performed by using the response factor obtained at 254 nm for the 4-nitro-DPA compound. Since these compounds eluted near the standard reference peak and the molar absorptivities at 254 nm for many of the mononitro and dinitro compounds are similar, then little error was probably introduced in their quantitation. The amount of these compounds formed was then multiplied by two and included with the amounts found from the mononitro- and N-nitroso-DPA compounds. At high NOz concentrations, the dinitro compounds accounted for about 1-2% each of the total product distribution. Thus, failure to account for their presence will result in only a slight error in the ambient NO2 measurement.
ANALYTICAL CHEMISTRY, VOL. 56, NO. 11, SEPTEMBER 1984
1823
Table I. NOz Collection and Recovery Efficiency Study PPb NOzn generated
flow rate,
vol sampled,
L/min
L
found front
88.0
0.5 1.0
715 1430 2940 3060 4080
83.2 44.9 22.0 14.1 10.8
44.0 22.0 14.7 11.0
2.0 3.0 4.0
PPb NOzb
PPb NO2 found
%
backup
recovery
0 0 0 0 0
94.6 102.2
100.1 96.0 98.0
av 98.2
& 3.1
Generated from NOz permeation system. Amount found in front cartridge based on recovery of total NOz products. Recovery based on four determinations for each concentration level.
3 5
6
6
8
10
12
Time IminJ
Flgure 5. Sample chromatogram obtained for a 1430-L sample of a 44 ppb NOp air stream from the permeation system, sensitivity 0.04 AUFS: (1) 4,4’dinitro-DPA, (2) 4-nitro-DPA, (3)N-nitroso-DPA, (4) 2,4’dinitro-DPA, (5) DPA, (6) 2-nltro-DPA.
As stated earlier, the amount of NOz in the air sampled was quantified by first determining the amount in pmol/mL of each of the NOz-DPA reaction products formed by using the corresponding product calibration standards. Then, the total number in pmol/mL of all the NO2 products was calculated and this number was directly related on a molar basis to the NO2 concentration in the air stream sampled. Method Validation. The NOz collection efficiency of the method was determined by passing known amounts of NOz vapors generated from the permeation system through two cartridges connected in series. The concentration of NO2 sampled was varied from 11to 88 ppb by varying the dilution gas flow rate from 4.0 L/min to 0.5 L/min, respectively. Consequently,the total gas volume sampled varied from about 4080 L to 715 L for the lowest and highest NOz concentrations generated. The cartridges were eluted with 2 mL of methanol and the NO2-DPA products analyzed by HPLC. These results, which are summarized in Table I, show that the NOz collection efficiencywas about 100% in a single cartridge. No detectable amounts of NOz were present in the backup cartridge. The overall recovery of the NO,-DPA products as determined by
HPLC ranged fom 95 to 102% with an average of 98.2 f 3.1% for four determinations at each NOz concentration level given in the table. These findings indicated that NOz was quantitatively collected and recovered from these cartridges even at flow rates up to 4.0 L/min. Sample capacity studies performed on the cartridges revealed that about 4 pmol of NOz can be quantitatively collected in a single cartridge. This corresponds to about 96 ppb NOz for a 1000-L air sample. Accordingly, at ambient NO2 concentrationsof 5-10 ppb, a single cartridge should last about 6 days at 1.0 L/min and about 3 days at 2.0 L/min. However, for extended sampling periods (>1 day), a backup cartridge should be used to ensure that no breakthrough due to channeling has occurred. A calibration plot was obtained by sampling 2000 L of air at 2.0 L/min through a single cartridge in which the NOz concentration was varied from 0.44 to 44 ppb. A linear regression analysis of the data indicated the curve has a slope of 0.934, a y intercept of 0.233 ppb NO2, and a correlation coefficient of 0.999. The closeness of the slope to unity shows the excellent correlation obtained between the amount of NO2 sampled and the amount of NOz recovered. The curve was also found to be linear up to 95 ppb NOz for a 1000-L air sample. Although, no breakthrough was observed at 95 ppb NOz, an additional backup cartridge should be used increase the sample capacity and linear range at higher concentrations. Sensitivity a n d Detection Limits. The detection limit for NO2 was calculated for a 2OOO-L air sample, a 2-mL elution volume, and a signal to blank (SIB)ratio of 3. Generally, a very small blank peak due to N-nitrosodiphenylamine was present. This blank peak corresponded to about 0.03 ppb for a 2000-L air sample. At a SIB ratio of 3, the calculated detection limit was about 0.1 ppb NOz. This detection limit was defined for a 2900-L air sample which corresponded to an 8-h sampling period a t 4.0 L/min or to a 16-h sampling period at 2.0 L/min. Rural ambient NO2measurementsmade by Wolff et al. (34) showed daily average NOz concentrations of a few parts per billion. Consequently, the method has adequate sensitivity for rural ambient NO2monitoring and is ideally suited for this application. Interferences. Possible interferences with the method from common ambient species such as NO, OB,“Os, SO2, and PAN were investigated along with possible humidity effects. Interference from NO at two concentration levels was investigated by passing 120 L each of 0.1 and 1.0 ppm NO calibration gas standards through separate cartridges. The cartridges were then eluted and analyzed by HPLC. The results showed that neither the 0.1 nor the 1.0 ppm NO gas mixtures produced any detectable NO2 products. Adsorption of NO by the cartridges was checked by passing the 1.0 ppm NO calibration gas through a single cartridge connected in series with a chemiluminescent NO, analyzer. The results showed that NO was not adsorbed and passed through the
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ANALYTICAL CHEMISTRY, VOL. 56, NO. 11, SEPTEMBER 1984
Table 11. SOz Effects on NOz Sample Recoveryn ppb SOz/ppb NOzb
S02/N02ratio
125122 50122 25/22
5.7 2.3 1.1
%
recoverye
Table 111. Relative Humidity Effects on NOz Sample Recovery'
102.0 98.2 99.0 av 99.7 f 2.0
% RH
% recoveryb
75% RH) humidities would have any significant effect on the method. Storage Stability. With this method, the samples must be shipped to the laboratory for analysis and, therefore, must not degrade with time. In order to investigate the stability of the collected NOz samples, we collected four side-by-side
ANALYTICAL CHEMISTRY, VOL. 56, NO. 11, SEPTEMBER 1984
1825
Table V. Sampling Rate Effects on Ambient NOz Measurements
date'
timebEDST
sampling rate, L/min
vol sampled, L
PPb NO*
% RSD
5.3
6/6-61 7
1A 1B 2A 2B
1430-1030
2.15 1.83 1.04 1.05
2581 2192 1251 1263
15.5 15.4 14.1 16.0 av 15.3 f 0.8
618-619
1A 1B 2A
10:50-11:OO
1.95 1.85 1.06
2785 2699 1515
14.4 11.7 13.5 av 13.2
6/94/10
(I
sample no.
1A 2A 2B
m20-1010
2.19 0.98 1.05
3021 1375 1393
* 1.4
10.6
21.7 24.1 24.8 av 22.5 f 1.6
6.9
6120-6121
1A 1B 2A 2B
02:45-07:45
0.94 1.04 1.02 0.88
1088 980 1002 1161
19.8 21.5 18.7 19.0 av 19.8 f 1.2
6.1
6/21-6122
1A 1B 1c 1D
07:55-11:45
1.02 0.97 1.12 1.09
1703 1620 1862 1823
18.8 18.2 18.2 17.8 av 18.3 f 0.4
2.2
Sampling conducted during June 1983. bTime of day at start and end of sampling period (Eastern Daylight Savings Time).
24-h air samples and analyzed one sample a week for 4 weeks. All four samples gave average NOz concentrations of 8.5 f 0.4 ppb. This result corresponded to a relative standard deviation of less than 5% over the 4-week period. The cartridge blanks were analyzed over a 3-month period and found not to increase with storage. Stability studies conducted with the standards revealed that the standards are stable up to 1 month without refrigeration and up to 2 months with refrigeration. These results indicated that the samples can be transported, stored, and analyzed at least up to 4 weeks after collection without any significant sample loss or degradation. Field Sampling. The method was used to monitor daily ambient NO2 levels in Warren, MI; the results of our field study are summarized in Table IV. Generally, two to four replicate samples were obtained during each sampling period. A sampling period consisted of 24-72 h at a sample flow rate of 1.0-2.0 L/min. Two cartridges connected in series were used for both the higher flows (-2.0 L/min) and the extended (72 h) sampling periods while a single cartridge was used for the lower flows (- 1.0 L/min) and the shorter (24 h) sampling periods. The air volume sampled by the cartridges a t the various flows varied from 1200 to 4000 L for each sampling period. The data show that the relative standard deviation of the individual samples ranged from about 2.2 to 13% for each sampling period. The average of the relative standard deviations for all the sampling periods was 7.6%. This number takes into account all the replicate samples that were obtained at both low and high flows and is a good indicator of the daily precision that is expected with the method. The samples were collected without any flow controlling devices on the Dynapumps. Flow rate changes over the extended sampling periods were observed which could have resulted in the higher standard deviations associated with some of the samples. Accurate flow control in the sample pumping system is a limiting factor in the ultimate precision obtained with the method. However, an overall field use precision of 7.6% is quite good for routine use of the method.
Table VI. Indoor NOz Measurements Using the NO2 Cartridgesa house
room
1
kitchen kitchen bedroom kitchen living room living room kitchen kitchen bedroom
2
3
cookingb stove
samplingc time
ppb NOz
electric electric
8-10 a.m. 10-12 a.m. 1-3 p.m. 9-11 a.m. 3-5 p.m. 7-9 p.m. 8-10 a.m. 10-12 a.m. 2-4 p.m.
23.1 15.5 20.4 2.0 36.1 12.5 144.8 41.4 34.3
electric gas gas
All samples represent 120-L samples. *Indicates whether gas or electric cooking stove was present in the kitchen. Time of day at start and end of sampling period. Table V shows that similar results were obtained for samples collected at both high and low flow rates. This is an important finding since it allows the operator greater flexibility in optimizing the sample flow rate to best match the expected NOz levels in order not to exceed the cartridge sample capacity over extended sampling periods. It was noted during field testing that the cartridges failed to trap NOz at ambient temperatures in excess of 90 OF. Upon elution with methanol, the cartridges produced no product or excess reagent peaks. Apparently, the diphenylamine reagent was volatilized from the sorbent at the high sampling temperatures, thus preventing NO2 absorption. To alleviate this problem, the cartridges were placed inside our atmospheric sampling trailer and a Teflon sampling line was connected from the cartridges to an outside sampling point. More research is being conducted to understand this effect. However, for routine field use, the cartridges should be sheltered in a cooler environment as a precautionary measure. The method was also applied to measuring indoor NOz levels in homes which have either gas or electric cooking
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ANALYTICAL CHEMISTRY, VOL. 56, NO. 11, SEPTEMBER 1984
appliances. Table VI summarizes the results of several homes that were tested in which air from various room was sampled by a single NO2 cartridge with the Gilian constant flow air sampling pump. The data show that the cartridges were able to monitor the indoor NO2 levels among the various rooms of the house sampled. This study shows that these cartridges can be potentially useful in the indoor or personal exposure monitoring field. ACKNOWLEDGMENT The author acknowledges the assistance of William Scruggs in all aspects of the experimental work. The author also acknowledges the assistance of Steven Cadle, Patricia Mulawa, and Andrew Schneiner for preparing and assisting in the PAN and “OB interference studies. The author also appreciates the assistance of David Rounbehler to Therm0 Electron Corp. for many helpful discussions on nitrosamine formation and for the preparation of the blank sorbent cartridges. Finally, the author thanks Keith Olson for performing the GC/MS analysis of the unknown product peaks. Registry NO. DPA,122-39-4;PAN, 227822-0;NO2,10102-44-0; Florisil, 1343-88-0. LITERATURE CITED (1) Grosjean, D., Ed. “Nkrogeneous Alr Pollutants: Chemical and Biological Impllcatlons”; Ann Arbor Science: Ann Arbor, MI, 1979. (2) Bailey, R. A.; Clark, H. M.; Ferris, J. P.; Strong R. L. I n “Chemlstry of the Envlronment”; Academlc Press: New York, 1978. (3) Committee on Medlcal and Biological Effects of Environmental Pollutant# “Nltropn OxMes”; National Research Councll, National Academy Press: Washington, DC, 1977. (4) Lin, S.C.; Kley, D.; McFarland, M. J. Geophys. Res. 1980, 85, 7546. (5) CharmeMes, W. L.; Walker, J. C. G. J. Geophys. Res. 1973, 7 8 ,
8571. (8) Galloway, J. N.; Likens, 0. E. Atmos. Envlron. 1981, 15, 1081. (7) Spicer, C. W. Envlron. Scl. Technol. 1983, 17, 112. (8) Fontlnjin, A.; Sabadell, A. J.; Ronco, R. J. Anal. Chem. 1970, 42, 475. (9) Clyne, M. A. A.; Thrush, B. A.; Wayne, R. P. Trans. Faraday SOC. 1984. 60,3590. (IO) Clough, P. N.; Thrush, B. A. Trans. Faraday SOC. 1987, 6 3 , 915. (11) Sigsby, J. E., Jr.; Black, F. M.; Bellar, T. A.; Klosterman, D. L. Envlron . Scl. Technol. 1973, 7 , 51. (12) Winer, A. M.; Peter, J. W.; Smlth, J. P.; Pitts. J. N., Jr. Envlron. Scl. Technol. 1974, 8,1118.
(13) Maeda. Y.; Aokl, K.; Munemorl, M. Anal. Chem. 1980, 52, 307. (14) Wendel, G. J.; Stedman, D. H.; Cantrell. C. A,; Damraure, L. Anal. Chem. 1983, 5 5 , 937. (15) Poizat, 0.;Atklnson, G. H. Anal. Chem. 1982, 5 4 , 1485. (16) Platt, U.; Permer, D.; Patz, H. W. J. Geophys. Res. 1979, 8 4 , 6329. (17) ReM, J.; Shewchun, J.; Garslde, B. K.; Balllk, E. A. Appl. Opt. 1978, 17, 300. (18) Reid, J.; El-Sherblnv, M.; Garslde, B. K.; Balllk, E. A. Appl. Opt. 1980, 19, 3349. (19) Kley, D.; McFarland, M. Atmos. Technol. 1980, 12, 63. (20) Saltzman, B. E. Anal. Chem. 1954, 26, 1949. (21) Jacobs, M. 6.; Hochhelser, S. Anal. Chem. 1958, 30,426. (22) Levaggl, D. A.; Siu, W.; Feldstein, M. J. Alr Pollut. Control Assoc. 1973, 22, 30. (23) Palmes, E. D.; Gunnlson, A. F.; DlMattlo, J.; Tomczyk, C. Am. Ind. Hyg. Assoc. J . 1978, 3 7 , 510. (24) Palmes, E. D.; Tomczyk, C. Am. Ind. Hyg. Assoc. J . 1979, 4 0 , 588. (25) Scientlflc and Technical Report on Nltrosamlnes EPA 60016-77-001 Unlted States Environmental Protection Agency, Research Triangle Park, NC, 1977. (28) Challls, 8. C.; Edwards, A.; Hunmer, R. R.; Kyrtopoulous, S. A.; Outranl, J. I n ”Environmental Aspects of N-Nitroso Compounds”; Walker, E. A., Castegnaro, M., Crlcuke, L., Lyle, R. E., Eds.; International Agency for Research on Cancer: Lyon, France, 1978;IARC Scientlflc Publlcations No. 19. (27) Hanst, P. L.; Spencer, J. W.; Miller. M. Environ. Sci. Technol. 1977, 11, 403. (28) Challis, B. C.; Kyrtopoulous, S. A. Br. J. Cancer 1977, 3 5 , 693. (29) Rounbehler, D. P.; Reisch, J. W.; Coombs, J. R.; Fine, D. H. Anal. Chem. 1980, 52, 273. (30) Rounbehler, D. P.; Reisch, J. W.; Fine, D. H. I n “N-Nltroso-Compounds: Analysis, Formation, and Occurrence”; Walker, E. A,, Castegnaro, M., Griculte, L., Biirzonyl, M., Eds.; International Agency for Research on Cancer: Lyon, France, 1980;IARC Scientlfic Publication
No. 31. (31) Argus, M. F.; Hoch-Ligeti, C. J. Natl. Cancer Inst. 1981, 2 7 , 695. (32) Chang, S.K.; Kozenlauskas. R.; Harrlngton, G. W. Anal. Chem. 1977, 4 9 , 2272. (33) Barsotti, D. J.; Pyiypin, H. M.; Harrington, G. W. Anal. Lett. 1982, 15, 1411. (34) Kelly, N. A.; Wolff. G. T.; Ferman, M. A. Atmos. Environ. 1982, 16, 1077. (35) Nellsen, T.; Hansen, A. M.; Thomsen, E. L. Atmos. Envlron. 1982, 16, 1. (38) Splcer, C. W.; Holdren, M. W.; Keigley, G. W. Atmos. Environ. 1983, 17, 1055. (37) Lewls, T. E.; Brennan, E.; Lonneman, W. A. J. Air Pollut. Control. Assoc. 1983, 33,885. (38) Harrls, G. W.; Carter, W. P. L.; Wlner, A. M.; Pitts, J. N.; Platt, U.; Perner, D. Environ. Sci. Technol. 1982, 16, 414.
RECEIVED for review January 24, 1984. Accepted April 26, 1984.
