Anal. Chem. 1988. 58. 1857-1805
a,4-dimethylstyrene, 1195-32-0;3,5-dimethylstyrene, 5379-20-4; phenyl ethyl ether, 103-73-1; 2,3-dimethylstyrene, 40243-75-2; 3,4-dimethylstyrene, 27831-13-6; methylindene, 29036-25-7; naphthalene, 91-20-3; benzo[b]thiophene, 95-15-8; methylbenzo[b]thiophene, 31393-23-4; 2-methylnaphthalene, 91-57-6; 1-methylnaphthalene, 90-12-0; 1-phenylethyl tert-butyl ether, 90367-83-2; biphenyl, 92-52-4; 1-ethylnaphthalene, 1127-76-0; dimethylbenzo[blthiophene, 30027-44-2; 2,6-dimethylnaphthalene, 581-42-0; 2,7-dimethylnaphthalene,582-16-1; 1,3-dimethylnaphthalene, 575-41-7; 1,7-dimethylnaphthalene,575-37-1; 1,6dimethylnaphthalene,575-43-9; 2,3-dimethynaphthalene,581-40-8; 1,4-dimethylnaphthalene,571-58-4; acenaphthalene, 208-96-8; 1,2-dimethylnaphthalene,573-98-8; acenaphthene, 83-32-9; 4methylbiphenyl, 644-08-6;3-methylbiphenyl, 643-93-6; dibenzcfuran, 132-64-9;fluorene, 86-73-7; dimethylbiphenyl, 28013-11-8; methylbenzofuran, 25586-38-3;bis(phenylethy1)ether, 93-96-9; 2-methylfluorene, 1430-97-3; 1-methylfluorene, 1730-37-6; 9fluorenone, 486-25-9; dibenzothiophene,132-65-0;phenanthrene, 85-01-8;anthracene, 120-12-7; sulfur, 7704-34-9; fluoranthene, 206-44-0; pyrene, 129-00-0; benzo[c]phenanthrene, 195-19-7; benz[a]anthracene, 56-55-3; chrysene, 218-01-9; triphenylene, 217-59-4; benzo[a]pyrene, 50-32-8; benzo[e]pyrene, 192-97-2; n-undecane, 1120-21-4;n-dodecane, 112-40-3;n-tridecane, 629ijo-5; n-tetradecane,629-59-4;2,6,10-trimethyltridecane,3891-99-4; n-pentadecane, 629-62-9; n-hexadecane, 544-76-3; norpristane, 3892-00-0; n-heptadecane, 629-78-7; pristane, 1921-70-6;n-octadecane, 593-45-3; phytane, 638-36-8; n-nonadecane, 629-92-5; n-hexadecanoic acid, 57-10-3; n-eicosane, 112-95-8;n-heneicosane, 629-94-7; n-docosane, 629-97-0;n-tricosane, 638-67-5; n-tetracosane, 646-31-1; n-pentacosane, 629-99-2; n-hexacosane,630-01-3; n-heptacosane, 593-49-7; n-octacosane, 630-02-4; n-nonacosane, 630-03-5; perylene, 198-55-0;dioxane, 123-91-1;dichlorobenzene, 25321.22-6; trichlorobenzene, 12002-48-1.
1857
McMuttrey, K. D.;Wildman, N. J.; Tai, H. Bull. Environ. Toxicol. 1983, 31 734-737. van Graas, 0.; de Leeuw, J. W.; Schenck, P. A. in Advances h Organic Geochemistry 1979; Douglas, A. G.,Maxwell, J. R., Eds.; Pergamon: London. 1980 DD 485-494. van de W n t I D.; Brown, S. c.; philp, R. P.; Simonett, B. R. T. GWchlm. C o s m h l m . Acta W80, 4 4 , 999-1013. van de Meent, D.; de Leeuw, J. W.; Schenck, P. A. J. Anal. Appl. fvrol. 1980. 2 . 249-263. Schenck, P.' A.; de Leeuw, J. W.; Viets, T. C.; Haverkamp, J. I n Petroleom, Geochemkf?y and Exploration of Europe; Brooks, J., Ed.; Blackweil Scientlfic: 1983; pp 267-274. van der Kaaden. A.; Boon, J. J.; de Leeuw, J. W.; de Lange, F.; Schuyi, P. J. W.; Schulten, H. R.; Bahr, U. Anal. Chem. 1884, 56, ~
2160-2164. SaizJimenez, C.; de Leeuw, J. W. Org. Geochem. 1984, 6 ,
287-293. SaizJimenez, C.; de Leeuw, J. W. Org. Geochem. 1984, 6 ,
417-422. Nlp. M.; de Leeuw. J. W.; Schenck, P. A.; Meuzeiaar, H. L. C.; Stout, S. A.; Given, P. H.; Boon, J. J. J. Anal. Appl. Pyrol. 1985, 8 ,
22 1-239.
de Leeuw, J. W.; Maters, W. L.; van de Meent, D.; Boon, J. J. Anal. Chem. 1977, 49, 1881-1884. Crisp, P. T.; Ellis, J.; de Leeuw, J. W.; Schenck, P. A. Anal. Chem. 1886, 58, 258-261 Giger, W.; Schaffner, C. Anal. Chem. 1978, 50, 243-249. Grob, K. HRC CC , J High Resolut Chromatogr . Chromatogr . Com mun. 1978. 1 , 263-267. Grob, K.; &ob, K., Jr. J. Chromatogr. 1978, 151, 311-320. Trestianu, S.; Gaii, M.; Grob, K., Jr. HRC CC, J. High Resolut. Chromatoaf. Chromatwr. Commun. 1978. 2 . 366-370. R & ? f ? y of Mass -Spectral Data; Stenhagen, E., Abrahamson, S., McLafferty, F. W., Eds.; Wiiey: New York, 1974; Voi. 1-4. Lee. M. L.; Vassilaros, D. L.; White, C. M.; Novotny, M. Anal. Chem. 1979, 51, 768-773. de Leer. E. W. 8.; Baas, M.; Erkeiens, C.; Hoogwater, D. A,; de Leeuw, J. W.; Schuyl, P. J. W.; de Leur, L. C.; Graat, J. W. I n Proceedings of the Internationel Conference on New Frontlers for Hazardous Waste Management; Pittsburgh, PA, Sept 15-18, 1985. Irwln. W. J. J. Anal. Appl. Pyrol. 1979, 1 , 3-25.
.
(17) (18) (19)
(20)
.
LITERATURE CITED (1) Hunt, D. F.; Shabanowltz. J.; Harvey, T. M.; Coates, M. Anal. Chem. 1985, 5 7 , 525-537.
RECEIVEDfor review August 5,1985. Accepted March 24,1986.
Sampling and Determination of Gas-Phase Hydrogen Peroxide following Removal of Ozone by Gas-Phase Reaction with Nitric Oxide Roger L. Tanner,* George Y. Markovits,' Eugene M. Ferreri, and Thomas J. Kelly Environmental Chemistry Division, Department of Applied Science, Brookhaven National Laboratory, IJpton, New York 11973
A method for the determlnatlon of hydrogen peroxide In the amblent atmosphere is described, using bnplnger or dlffuslon scrubber collectlon of H,02 wlth aqueous-phase analysis by an enzyme-catalyzed fluorescence technique. Interference from ozone at amblent levels Is removed by gas-phase reactlon wtth excess nltrlc oxlde. The lmplnger and dMuslon scrubber collectlon technlques glve equlvalenl results for atmospherlc gas-phase H202wtth h l t s of detectkn of 0.1 ppbv for approximately 60-mln and 10-mln sampllng times, respectlvely
.
The development of techniques for measuring gaseous and aqueous HzOz and other hydroperoxy compounds has been the focus of substantial research effort following the recogPermanent address: Practical Engineering College of BeerSheva, P.O. Box 45, Beer-Sheva, Israel. 0003-2700/86/0358-1857$01.50/0
nition that HzOzcould rapidly oxidize dissolved S(1V) compounds to sulfuric acid throughout the normal p H range of rain, cloud, and fog waters (pH 2-7) (1,2).The high solubility of HzOzin water (Henry's law constant lo5 M atm-') leads to significant aqueous concentration (1-100 MM)in, e.g., cloud water, even a t low parts-per-billion by volume gaseous HzOz concentrations in air entering clouds (3-5). Several methods for determining aqueous-phase HzOz in atmospheric samples have been developed or improved recently based on luminol chemiluminescence (61,(p-hydroxypheny1)acetic acid (POHPAA) dimer fluorescence (5, 7-9),scopoletin fluorescence quenching (lo),and peroxyoxalate chemiluminescence (I1). Measurements of gas-phase hydrogen peroxide have been attempted by collection of the peroxide in aqueous solution using impingers or condensation collection devices (12). However, these efforts have been shown to give unreliable resulta due to the in situ formation of hydrogen peroxide from low-solubility constituents of ambient air and/or compressed air during collection (13-15).It has been suggested that this
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0 1986 Amerlcan Chemical Society
1858
ANALYTICAL CHEMISTRY, VOL. 58, NO. 8, JULY 1986
Table I. Output of H202 Gaseous Source as a Function of Carrier Gas Flow, Dilution Air Flow, and Time AMASS
FLOW METER
date of measurementa
NEEDLE VALVE
1 2
REGUL AT0R TO MIXING CHAMBER
COMPRESSED ,"--BREATHING
I
1i I
3 10 10
carrier gas flow dilution air rate, cm3 flow rate, L min-' min-* 31.2 31.4 9.2 44.8 46.5
1.44 4.42
5.35 4.28 4.12
~H2021
after [H2Oz] at dilution, output of atm source, (ppbv) atm (ppbv)b 12.0
566
4.0
567 583 570 556
1.0
5.9 6.2
"Day 1 = date of preparation. bMean value (kSD), f = 568 (*lo).
,/
TH'ERMOSTATTED BATH
POROUS TEFLON TUBE
Figure 1. Gaseous hydrogen peroixde source employing Teflon diffusion tube.
a porous
"artifact" HzOz may be formed by decomposition of stable constituents such as ozone (16) or possibly by aqueous-phase recombination reactions of scavenged free radicals (17). Recent observations of ozone loss and peroxide formation suggest that surface-mediated decompositon of ozone via HO; and Of- intermediates may be the mechanism of artifact formation (16). This suggestion is, in part, based on previous studies of O3 decompositon in aqueous solution (18), but supporting evidence concerning mechanisms is limited. Artifact formation is reportedly enhanced by using Teflon impingers (16) or condensation collection (15)to remove gaseous HzOzfrom ambient air. A new technique for artifact-free sampling and analysis of gas-phase HzOz has been reported (19),which relies upon analysis of HzOz immediately after collection to minimize artifact formation. We report in this work an alternate technique for the measurement of gas-phase hydrogen peroxide based on the simple expedient of removing co-present gas-phase ozone by reaction with excess nitric oxide. It will be demonstrated that the resulting ozone-free air can be scrubbed of ambient gas-phase peroxide without positive interference ("artifact" formation) using either a conventional midget impinger or a diffusion scrubber device (20), with equivalent analytical results. Negative interference from dissolved SOz in the determination of collected Hz02(g)by the POHPAA technique can be significant for both the impinger and diffusion scrubber techniques for high ambient SOz levels (10-60 ppbv), but is easily circumvented by collecting in millimolar aqueous formaldehyde solution. Limits of detection for both impinger and diffusion scrubber sampling methods are -0.1 ppbv for sampling times of about 60 min and 10 min, respectively. EXPERIMENTAL SECTION Reagents. Nitric oxide (-200 ppm) in N2was obtained in cylinders from Scott Specialty Gases, Plumstedville, PA. Horseradish peroxidase, (p-hydroxypheny1)acetic acid (POHPAA), and catalase reagents were highest purity from Sigma Chemical Co. The remaining reagents (Tris buffer, Na4EDTA, 3% H202 solution) were reagent grade materials used as received. Concentrated POHPAA reagent is prepared by mixing 3.03 g of Tris, 0.095 g of Na,EDTA, 1.15 g of POHPAA, and 3.0 mg of horseradish peroxidase to water containing 1 mL of 3 M HC1 and diluting to 50 mL. Dilute POHPAA reagent is prepared daily by 12.5-fold dilution of concentrated reagent; prepared reagents are stored at 4 "C. Formaldehyde solutions were prepared by dilution of reagent grade aqueous formaldehyde.
Gaseous H2OZSource. Most experiments reported below were performed by using a novel, porous Teflon source of gaseous HzOZ. This source, shown in Figure 1, is similar to that reported by Hwang and Dasgupta (21). A length (ca. 8 cm) of porous Teflon tubing (Gore-tex, 0.6 cm o.d., 50% porosity, W. L. Gore and Associates, Elkton, MD) was immersed in an aqueous solution of H20z to 1 M but typically 0.01 M) in a 100 cm3 polyethylene bottle, the latter immersed in a constant-temperature bath (30 f 0.1 "C). A flow of compressed air was passed through the FEP Teflon tube as a carrier stream for H202vapor; this flow was controlled by a needle valve and monitored continuously with a mass flowmeter (Tylan FM-360). The carrier flow exiting the source was diluted with a much larger flow of air before being supplied to the sampling system. The porous Teflon material has a low bubble pressure; hence, in order to prevent leakage of the aqueous H20z solution through the tubing walls, it was necessary to self-pressurizethe solution by sealing the polyethylene bottle in which it was contained. The output of the source as a function of carrier and dilution gas flows is given in Table I. Under the conditions of the experiment the output concentration is stable at a concentration of 568 f 10 ppbv (5.68 X atm) before dilution, and long-term drift is less than 10%/month. The steady-state gaseous concentration is approximately the calculated Henry's law concentration, based on reported Henry's law constants, which range from 9.0 X lo4 to 1.4 X lo5 M atm-' at 20 "C (21-23). The device thus generates a constant concentration, with the source output rate (moles/unit time) proportional to the carrier flow rate. Tests have also shown that the source output concentration is independent of the length of the porous Teflon tube for tube lengths exceeding a few centimeters, indicating that Henry's law equilibrium for H202is attained within a few centimeters downstream of the entrance to the porous tube. Lower H20zconcentrations can be generated by gaseous dilution in preference to changing the aqueous-phase concentration of HzOzor changing the temperature, though changing the flow rate through the source requires up to 24 h for reequilibration. Only the short-term stability and long-term drift of the source output are important for calibration of the analytical method. Laboratory Apparatus for Ozone Interference Studies. The elimination of H20zformation in gas-to-aqueous scrubbing devices by reaction of gas-phase ozone with nitric oxide has been studied by using a procedure previously described (24). Briefly, laboratory studies were performed by using a source of clean air that could be split into two streams after ozone, water vapor, and/or HzOz were added. A small flow of NO in N2 was added to one of the air streams, upstream of a mixing chamber. A series of the three midget impingers collected the HzOZin each stream; flow rates were measured by appropriate flowmeters; and an ozone monitor (Monitor Labs, Model 8410, ethylene-chemiluminescence instrument) measured the concentration of ozone both upstream and downstream of the impingers. Ozone was generated with an ozone generator (AID Model 565). Operation of the ozone generator with air appears to generate H202as well as N(V) oxides and oxyacids; using Oz to generate O3 still producers small quantities of HzOz;hence, the generator gas stream was scrubbed in a water filled bubbler prior to its addition to the sample air stream. In initial studies, H202was generated by use of capillary diffusion source (25);for SOz interference studies SOz was added
ANALYTICAL CHEMISTRY, VOL. 58, NO. 8, JULY 1986
SECT I ON \
"--18 Mi? cm-*). This peroxide is formed (and scavenged by the POHPAA reagent) at varying rates depending on storage conditions (28). This probably accounts for the increasing background in prepared POHPAA reagent blank in which the
enzyme horseradish peroxidase is present. The background fluorescence is significant (equivalent to 0.50 p M HzOz in freshly prepared reagent) and has been observed to increase at up to 0.025 pM h-' under conditions of daylight and variable temperature (25-35 "C). At stable temperatures 120 O C in the dark, the background increase is more typically 0.010 p M h-l. During measurements of ambient gas-phase HzOzit is necessary that background measurements of reagent fluorescence be taken frequently, preferably between each sample, in order to attain the LOD of 0.02 p M stated above. Interference Studies. Elimination of artifact HzOzformation in impinger collection of gaseous peroxides from ozone-containing air was the motivation for the development of the reported method. The effectiveness of gas-phase reaction of ozone with nitric oxide in preventing artifact HzOz formation in impingers during collection is demonstrated by the laboratory data shown in Table 111. In-solution production of HzOz was prevented by adding excess NO and allowing sufficient reaction volume (time) to reduce [O,]to about 1 2 ppb. Traces of HzOzfound in a few cases employing NO addition, for example in experiment 6, gas stream 2, were not significantly different from background. We note also that
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ANALYTICAL CHEMISTRY, VOL. 58, NO. 8, JULY 1986
the artifact formation observed from ozone-containing air was variable (experiments 3 and 6-8, gas stream l),even in laboratory experiments using commercially supplied compressed air as carrier, a result which has been observed by other workers. Repetition of these experiments using ambient and filtered ambient air yielded equivalent results: no artifact H,Oz formation in scrubbing solutions for ozone-free air; aqueous H,Oz concentrations corresponding to 1-10 ppbv in the gas phase formed in scrubbing solutions for ozone-containing air, presumably from O3 surface decomposition products. Since no negative signal was observed, these experiments also demonstrate the absence of positive and negative interferences with the method, within its precision and accuracy limits, from gaseous NO (6 ppm) and NOz (-300 ppbv from the N W 3reaction) under the sampling conditions used. Sampling of NO + NOz does produce nitrite and nitrate at micromolar levels in the impinger solution, but this does not interfere with the enzyme-catalyzed POHPAA determination of H,Oz(aq). The expected extent of negative interference from collection of SOz(g) along with HzOZin the impinger may be calculated by using the second-order rate constant of the dissolved S1"-H,02 reaction (2). For 1ppb HzOzand 5 ppb SOz at 20 "C and pH = 5-5.5 in the collection solution, the maximum rate is M s-' in 10 mL of HzO at the final accumulated bisulfite and HzOZconcentrations. This corresponds to an upper limit loss of 0.4 pM h-' of HZO2. Lower loss of H,Oz in the diffusion scrubber is predicted, since the gas-liquid contact time is less (-2 min) and samples can be promptly fixed after collection. Direct tests of these calculated loss rates were made by admitting SOz(g) from a permeation source to an air stream containing parts-per-billion levels of H,O,(g) and collecting these gases in water or POHPAA reagents. For [SO,], from 10 to 60 ppb, a negative interference in the determination of -20 ppbv H z 0 2of -1.5% per ppbv SO, was observed for collection in H,O and -0.7% per ppbv SOz for collection in POHPAA reagent. The apparent loss of HzOzincreased with [SO,] a t SOz concentrations greater than about 10 ppbv (corresponding to [HS03-] = 0.55 pM in the collected solution after 30 min). This observed loss is comparable to that predicted due to the direct reaction of HS03- and Hz02(aq): 0.1 pM averaged over a 30-min sampling period for 10 ppbv SOz and 20 ppbv HzOzcollected in 1 2 mL of HzO, or -1% loss per ppbv SO,. However, about the same interference (% loss/ppbv SOz) was observed for experiments performed a t - 5 ppbv H 2 0 2 even though average rates for the direct HS03--H202 reaction should be proportionately lower. In addition, collection in POHPAA reagent lowered but did not eliminate the negative interference, even though the peroxidase-catalyzed dimerization reaction has a half-life of
