Anal. Chem. 1989, 61, 187-189
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TECHNICAL NOTES Modification of a Hlgh-Efficiency Passive Sampler To Determine Nitrogen Dioxide or Formaldehyde in Air James D. Mulik,* Robert G. Lewis, and William A. McClenny Atmospheric Research and Exposure Assessment Laboratory, US.Environmental Protection Agency, Research Triangle Park, North Carolina 27711
Dennis D. Williams
NSI Technology Services Corporation, Research Triangle Park, North Carolina 27709 In three previous papers (1-3),we described the development and evaluation of a high-efficiency passive sampling device (PSD) for volatile organic chemicals in air. A commercial version of this PSD has subsequently become available. In the initial version, a granular sorbent, Tenax-GC, was used to collect the compounds of interest from air. This technical note describes the modification of the PSD by replacing the granular sorbent with filter paper treated with appropriate reagents to trap nitrogen dioxide (NO,) or formaldehyde.
EXPERIMENTAL SECTION Apparatus. The construction of the PSD has been previously described (I). It is a dual-faced sampler made up from a series of diffusion barriers placed on either side of a cavity for containment of collection media. The commercial device (Scientific Instrumentation Specialists, Moscow, ID) is supplied with a protective cage to prevent contamination of the outer diffusion barriers and with 0-ring-sealed caps for closure before and after exposure (see Figure 1). In this work, treated glass fiber filter paper (Whatman GF/B Glass Microfibre) waa used as the trapping medium. One treated filter was placed behind each set of diffusion barriers, on either side of the containment cavity. Reagents and Solvents. All reagents were of certified ACS grade or better. (2,4-Dinitrophenyl)hydrazine(DNPH) was Eastman Kodak 1866 (Rochester, NY). All solvents were glassdistilled from Burdick and Jackson (Muskegon,MI). Acetonitrile was also of UV grade. Procedure. Prior to treatment, the filter paper was cut with a circular stainless steel die to yield 33-mm-diameter filters. The filters were washed five at a time in a Buchner funnel with five 100-mL volumes of charcoal-filtered deionized water. They were then dried in a vacuum oven at 60 OC for 1 h and stored in a desiccator over anhydrous calcium sulfate until cooled to room temperature. For nitrogen dioxide, the filters were treated with a 1.68 M solution of triethanolamine (TEA) in acetone. Treatment was carried out in a glovebox under a nitrogen atmosphere by syringe addition of 0.5 mL of the TEA solution to the center of each fiter. After a period of 40 min to permit the solution to diffuse completely throughout the filters, they were removed from the glovebox, placed in a vacuum desiccator, and dried for 40 min at room temperature and ca.0.5 kPa The dried filters were placed in sealed plastic Petrie dishes and stored with activated charcoal in metal cans with compression-sealed lids ("paint" cans) until used. The treated filters were loaded into the PSD in the glovebox and the charged PSDs installed in their protective cages. The PSD assemblies were then placed in small (0.5 pt) cans, which were stored in larger (1gal) cans containing activated charcoal until exposed. To collect formaldehyde, the filters were coated with DNPH. Before use, the DNPH was purified by repeated recrystallization from acetonitrile, according to the procedure of Tejada (4). The reagent solution was made up to 0.01 M DNPH and 0.05 N
hydrochloric acid in acetonitrile, and 0.5 mL was used to treat each filter in the same manner described above. Analyses. After exposure, the treated filters were removed from the PSDs in a glovebox under nitrogen and placed in 35-mL screw-capped polypropylene bottles. For the TEA-coated filters, 10 mL of deionized water waa added to the bottle, which was then tightly capped and placed in a sonification bath at room temperature for 30 min. The anion extract was filtered through a Gelman Acrodisc disposable filter assembly, and 2 mL of the extract was injected into an ion chromatograph (IC) for determination of nitrite ion concentration. A Dionex Model 4000 IC equipped with Dionex HPIC AG4A precolumn, HPIC AS4A analytical column, and AMMSl anion micromembrane suppressor column was used for nitrite analysis. The eluent was aqueous sodium carbonate (0.0018 M) and ammonium bicarbonate (0.0017 M), and the regenerant was 0.025 M sulfuric acid. The flow rate waa 2 mL/min. The DNPH-coated filters were similarly extracted with 5 mL of acetonitrile, and 2 mL of the filtered extract was analyzed by high performance liquid chromatography (HPLC). For formaldehyde (and other aldehydes), a Du Pont Zorbax ODS column was used in the Dionex instrument. The mobile phase was 60% aqueous acetonitrile: flow rate 1mL/miq preasure, 1320 psig. The Dionex UV detector was set at 360 nm.
RESULTS AND DISCUSSION The effective sampling rate of the PSD for NOz was calculated from Fick's first law of diffusion (I)to be 154 cm3/min. For formaldehyde, the calculated rate was 103 cm3/min. The NO2 PSD was evaluated for linearity of response by exposure to known concentrations of the gas in purified air (Aadco Instruments 737 Generator, Clearwater, FL) at 20% relative humidity. In each trial, five PSDs were exposed simultaneously for 20-24 h in a 28-L poly(methy1 methacrylate) chamber (11cm X 15 cm X 183 cm long) to NOz levels of 20-450 pg/m3 generated by a permeation tube (VICI Metronics, Santa Clara, CA; 410 ng/min at 30 OC). Air velocity through the chamber was maintained a t 100 cm/s (measured in three places with a hot-wire anemometer). The NO2 concentrations in the chamber were monitored continuously with a Bendix Model 8101 NOx monitor. Figure 2 shows a linear regression plot of the NO2 generated vs that determined by the PSDs. Each point on the plot represents an average of five values obtained at a given chamber concentration. Agreement between the PSD results and the reference method was excellent over the full range of NO2 concentrations (correlation coefficient of 0.9955). Water vapor and nitric oxide (NO)were introduced into the chamber during some experiments to determine possible interferences. No interferences were observed a t 57% and 80% relative humidity or at the unusually high NO concentration of 91 pg/m3. Studies are currently under way to evaluate potential effects of water vapor at varying temperatures (-23 to 38 "C).
This artlcle not sublet3 to U.S. Copyright. Published 1989 by the American Chemical Society
188
ANALYTICAL CHEMISTRY. VOL. 61.NO. 2. JANUARY 15. 1989
0
20 40 MI 80 100
300
200
Face Velocity lcrnls) *re
1.
npM 4. Effect of face velocity MI PSD for NOp The exposwe hne was 2 h at each velocity and Hm chamber concentration was 135 pg/m3.
Passive sampling device
Table I. Comparison of Modified PSD with a Tunable Diode Laser for NO2 in Ambient Outdoor Air concn' hy
day 1
2 3 4 5
6 7 8 9
CONCENTRATION IN CHAMBER. rB/m3
10
w e 2. Linear regreash plot of NO? ccncentration measured by PSO vs chamber concentration. Each point represents the mean of five simultaneously exposed PSDS
11 12 13
overall av
outside mean o 21.9 17.2 20.8 18.3 11.8 11.8 17.4 19.7 23.1 13.9 13.9 11.9 6.7 16.9
0.68 1.22 0.94 0.92 2.52 1.76 1.11 1.02 1.43 0.42 1.09 0.54 0.13
PSD,rrg/ms inside chamber' mean
(I
23.6 17.8 21.4 21.4 15.9 11.3 16.0 19.7 21.7 21.2 20.2 18.9 9.7 18.8
5.30 1.87 2.85 4.28 1.88 3.02 3.62 4.50 5.40 5.02 3.86 0.81
0.91
concn hy tunable diode laser, rrglm'
mean
uncc
19.5 11.4 14.8 21.6 11.8
f2.9 f1.7 f2.3 i3.2 i1.7 f1.3 i2.5 i2.7 f3.8 f3.4 f3.4 i2.3 i1.3 f2.5
8.6 16.0 17.6 25.6 22.9 23.3 14.9 9.0 16.7
a Mean of three PSDs corrected to 20 ' C. bAmbientoutside air passed through chamber at 100 cm/s. eune is the estimated uncertainty of the real-time measurement based on analysis of absolute errors.
e
3
s
?)
I2
Is
Io
EXPOSVRE Tlur
21
24
27
30
n
3. h n t n y of NO, collected by PSO vs exposue time. Chamber concentration was 107 Irglm' NO,.
Figure 3 s h o w the quantity of NO2 measured by the PSD vs exposure times of 2,4,8, 16, and 24 h at a constant NO2 concentration (107 ag/m3). On the basis of the linearity of response and the sensitivity of the analytical method, it should be possible to determine concentrations of NO2 as low as 25 pg/m3 with an exposure time as short as 1 h. Studies were also conducted to determine the response of the NO2 PSD as a function of face velocity. Figure 4 shows the percent recovery of NO2 from air after 2-h exposures at face velocities ranging from 20 to 280 cm/s at a chamber
concentration of 135 rrg/m3. The response was found to be similar to that previously reported for volatile organic chemicals (I),indicating starvation effects due to boundary layer formation a t face velocities below 30 cm/s. Outdoor exposure trials were conducted over a period of 13 days, during which ambient temperatures ranged from 7 to 33 OC (average 19.3' C ) and atmospheric moisture content from 29 to 99% relative humidity. Triplicate sets of PSDs were exposed for 22 h in a parking lot under a small rain shelter, but were otherwise unshielded. A second set of three PSDs were simultaneously exposed inside a glass chamber (15-cm diameter x 91 em long) to air drawn in from the immediate vicinity of the outdoor set in such a manner as to achieve a constant air velocity of 100 cm/s across the faces of the PSDs. The results of exposures are given in Table I, along with simultaneous reference measurements obtained by means of a tunable diode laser system (5). Concentrations were calculated by assuming an average temperature of 20 "C. Despite the unexplained poorer precision observed in the chamber, there were no significant differences between the results obtained at constant face velocity and those obtained outdoors, where wind velocities ranged from 33 to 570 cm/s. Indoor exposure studies were carried out in eight households. In each home, duplicate sets of PSDs were exposed for 2C-24 h in the principal living area of each home next to
ANALYTICAL CHEMISTRY, VOL. 61, NO. 2, JANUARY 15, 1989
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Table 11. Indoor and Personal Air Measurements with NO, PSD concn bv PSD, household
rglh3
1 2 3 4 5 6 7 8
58.6 54.1 66.8 88.4 34.8 77.7 114.4 24.4
living area’ concn by chemilumin, clg/m3 52.6 54.5 50.8 69.6
’ADDroximate 22-h exDosure time.
52.6
20 58 35 30 85 36
486 239 302 518 155 401
13.2
55
381
concn,’ pg/m3 method
1
PSD
2 3
TO-llb PSD TO-11 PSD TO-11
4
outdoors, roof
PSD TO-11 TO-11
24 May 1988 to 25 May 1988 0700-1900 1900-0700 0700-1900 21.2, 27.2’ 32.8, 33.2 22.0 24.5 25.5 26.6 20.4 28.2 4.2
personal concn by PSD, pg/m3 daytimeb nighttime 34.7 76.3 56.8 73.3 28.0 55.6 40.1 139.5
50.9 51.2 61.7 67.6 24.5 48.3 32.2 41.5
bADDroximate12-h exposure time. ‘ADDroximate 8-h exDosure time.
Table 111. Indoor Air Measurements with Formaldehyde PSDs
office
kitchen during gas stove cooking exposure time, concn by PSD, min N/m3
38.4, 38.4 38.8, 41.0 28.6 31.8 29.1 31.8 30.6 4.9
‘Average temperature taken as 25 values represent collocated samples.
OC.
28.7 22.0 19.9 30.8 30.6 22.4 26.2 1.8
mean 29.8 33.7 24.2 25.4 28.5 29.2 24.4 27.2 3.6
bReference 7. ‘Paired
a Luminox LMA-3 chemiluminescence detector (6). A small (10-cm diameter) electric fan was employed to assure adequate air movement in the vicinity of the PSDs. In addition, one resident of each household wore a PSD for 12 h during the day, and kept a second PSD near the bedside during sleeping hours. During meal preparations using gas-fueled cook stoves, a third PSD was exposed near the stove for the period of time that the burners were operated. Results presented in Table I1 show good agreement between the PSDs and reference chemiluminescence method. Long-term indoor and personal exposure values were similar, ranging from ca. 20 to 90 pg/m3. However, NOz levels were found to be elevated by 5- to 15-fold during cooking activities. During these periods, NOz concentrations were easily measurable with the PSD in as little as 20 min. Laboratory evaluation of the formaldehyde PSD has not yet been completed. A recent incident of “sick building syndrome (SBS)”, however, prompted an indoor air quality study in which the new PSDs could be compared with an established pump-based formaldehyde method (4, 7). The results of collocated sampling are shown in Table 111. The agreement between the two sampling methods was shown to be good, and the PSDs were found to be more convenient to use and less obtrusive than the pump-based samplers. The formaldehyde levels determined were not atypical for older office buildings. Outdoor measurements are given for reference.
CONCLUSIONS In this and the preceding work, we have demonstrated the utility of a universal PSD for a broad spectrum of organic and inorganic gases in air. Eatough et al. (8)have also adapted the PSD to determine gas-phase nicotine. While other PSDs for NO2 and formaldehyde are commercially available, they are far less sensitive and require exposures of 4-7 days for nonoccupational environments. Most are also not designed for reuse. We have been encouraged by the accuracy obtainable with the PSDs reported here and plan future work to extend the device to other gaseous air pollutants such as ozone, ethylene oxide, and sulfur dioxide.
ACKNOWLEDGMENT We thank Silvestre B. Tejada of the U. S. Environmental Protection Agency, Research Triangle Park, NC, for valuable laboratory support in the analysis of samples for formaldehyde. Registry No. TEA, 102-71-6;NOz, 10102-44-0;formaldehyde, 50-00-0; (2,4-dinitrophenyl)hydrazine, 119-26-6.
LITERATURE CITED Lewis, R. 0.;Mulik, J. D.; Coutant, R. W.; Wooten, 0. W.; McMiiiin, C. R. Anal. Chem. 1985, 5 7 . 214-219. Coutant, R. W.; Lewis, R. G.; Mullk, J. D. Anal. Chem. 1985, 5 7 , 219-223. Coutant, R. W.; Lewis, R. G.; Mullk, J. D. Anal. Chem. 1988, 58, 445-448. Tejada, S. B., Int. J . Environ. Anal. Chem. 1986, 26, 167-185. Hastie, D. R.; MacKay, G. 1.; Iguchi. T.; RMley, B. A., Schiff, H. I. Environ. Scl. Technol. 1983, 17. 352A-364A. Schiff, H. I.; MacKay, G. J. Castledine, C.; Harris, G. W.; Tran, Q., Water Alr Soil Pollut. 1986, 30, 105-114. U.S. Environmental Protection Agency. Compendlum of Methods for the Determlnatlon of Toxlc Organic Compounds in Amblent Ak; Method TO-1 1, EPA-60014-84-041, Research Triangle Park, NC, 1988. Eatough, D. J.; Benner, C. L.; Bayona, J. M.; Caka, F. M.; Tang, H.; Lewis, L.; Lamb, J. D.; Lee, M. L.; Lewis, E. A.; Hansen. L. D. Roc. 1987 €PA IAPCA Symposlum on Measurement of Toxic and Related Alr Pollutants; APCA Publication ViP-8, Plttsburgh, PA, 1987, pp 132- 139.
RECEIVED for review August 17,1988. Resubmitted October 17,1988. Accepted October 21,1988. Although the research described in this technical note was funded wholly or in part by the US.Environmental Protection Agency through Contract 68-02-4444, it has not been subjected to agency review. Therefore, it does not necessarily reflect the views of the agency, and no official endorsement should be inferred. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
