Environ. Sci. Technol. 2002, 36, 4121-4126
Degradation of the Adsorbent Tenax TA by Nitrogen Oxides, Ozone, Hydrogen Peroxide, OH Radical, and Limonene Oxidation Products JACOB G. KLENØ, PEDER WOLKOFF,* PER A. CLAUSEN, CORNELIUS K. WILKINS, AND THORVALD PEDERSEN† Department of Indoor Climate, National Institute of Occupational Health, Lersø Parkallø 105, DK-2100 Copenhagen Ø, Denmark
potential indicators of irritating substances in air. The application of such indicators, however, assumes either specificity and/or a qualitative and quantitative knowledge of the species capable of forming them. The purpose of this work was 3-fold: (1) to identify Tenax degradation products from limonene-O3 mixtures and determine their oxidant specificity [Limonene was chosen because of its rapid reaction with O3 and its relatively high concentration and frequency of occurrence indoors (12).]; (2) to test hydrogen peroxide (H2O2) and the OH radical as potential products responsible for the degradation caused by limonene-O3 mixtures; and (3) to scrutinize the degradation products of Tenax caused by the common oxidants in indoor air, nitrogen oxide (NO), NO2, and O3.
Experimental Section The degradation of the adsorbent Tenax TA was studied qualitatively by sampling oxidants common in indoor air followed by thermal desorption and gas chromatography. A total of 25 degradation products were identified. Several degradation products not reported previously were identified: 9 for nitrogen dioxide; 11 for ozone; 2 for hydrogen peroxide; 12 for hydroxyl radical; 1 for ozonelimonene mixtures, but none for nitrogen oxide. Whereas ozone shows a complex degradation of the adsorbent, hydrogen peroxide and limonene-ozone mixtures show few products. Nitrogen dioxide and the hydroxyl radical behave almost identically and produce 2,6-diphenyl-pbenzoquinone as the major degradation product. Reactant specific degradation products were identified for ozone (11) and nitrogen dioxide (1).
Introduction Tenax is a synthetic polymer consisting of 2,6-diphenyl-pphenylene ether units used for sampling of volatile organic compounds with boiling points above approximately 50 °C. It is hydrophobic, thermally stable in the absence of O2, and has a low chromatographic background (1, 2). However, the application of adsorbents in general involves the risk of artifact formation. For example, terpenes may rearrange as a result of acid catalysis on the adsorbent (3). Ozone (O3) reacts with adsorbed terpenes to give increased amounts of oxidation products at the expense of the terpenes. This oxidative loss is pronounced for e.g. myrcene and limonene, whereas slowly reacting terpenes are practically unaffected by O3 (4, 5). Nitrogen oxides and O3 are reported to degrade Tenax (6-10). Nitrogen dioxide (NO2) mainly forms 2,6diphenyl-p-benzoquinone (DPQ) and 2,6-diphenyl-p-hydroquinone (DPHQ), whereas the degradation pattern of O3 is complex and includes the frequently reported benzaldehyde and acetophenone (1, 9, 10). Reaction mixtures of limonene and O3, which contain no residual O3, also degrade Tenax into DPHQ (10). These mixtures are known to be strong airway irritants (11). The reactive compounds that degrade Tenax in these mixtures could reasonably be identical to the strong irritants. Thus Tenax degradation products could be * Corresponding author phone: (+45) 39 16 52 72; fax: (+45) 39 16 52 01; e-mail:
[email protected]. † Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark. 10.1021/es025680f CCC: $22.00 Published on Web 08/24/2002
2002 American Chemical Society
Chemicals. Oxygen (99.999%), NO, NO2, and N2 (O2 + H2O < 2 ppm) were from Hydrogas, Norway. Acetophenone (>99.5%), benzoic anhydride (purum), decanal (97%), diphenylethanedione (98%), nonanal (97%), and phthalic anhydride (for syntheses) were from Fluka. Benzaldehyde (>99.5%), benzoic acid (>99.9%), hydrogen peroxide (35% in H2O), methanol (>99%), and phenol (>99.5%) were from Merck. Benzophenone (g99.0%), 2,6-diphenylphenol (98%), phenyl acetaldehyde (>90%), and phenylglyoxal hydrate (97%) were from Aldrich. p-Hydroquinone was from Kebolab, Denmark. Phenylglyoxylic acid (>98%) was from Sigma. Phenylmaleic anhydride (97%) and 1,2-diphenylethanone (97%) were from Lancaster Synthesis. 2,6-Diphenyl-p-benzoquinone (DPQ) and 2,6-diphenyl-p-hydroquinone (DPHQ) were synthesized (10), and 2,4-diphenyl-4-cyclopentene-1,3dione was prepared according to Ruggli and Schmidlin (13). Adsorbent tubes were Perkin-Elmer stainless steel tubes (length 31/2", outer diameter 1/4") packed with fresh and unused 200 ( 1 mg Tenax TA 60-80 mesh (Chrompack, The Netherlands). Tenax TA will be called Tenax throughout, if not otherwise stated. Tedlar sample bags were from SKC Inc., PA, U.S.A.; the volume was 25 L in all experiments. Instruments. Tenax samples were analyzed by thermal desorption-gas chromatography. A mass spectrometer (TDGC-MS) was used for identification and a flame ionization detector (TD-GC-FID) for quantification. The TD apparatus was a Perkin-Elmer ATD 400 with a plug of silanized glass wool only in a narrow/wide bore cold trap. The conditions were as follows: cold trap temperature -30 °C, outlet split flow 30 mL/min, desorption flow 46 mL/min, desorption time 20 min, transfer line and valve temperature 225 °C and desorption temperature of the adsorbent tube and the cold trap 300 °C. The outlet split was 1:16 due to the high desorption flow in the thermal desorber to get the higher boiling compounds through the system. Two different gas chromatographs were used: a Perkin-Elmer Auto system GC and a Hewlet Packard 5890 series II. Both were equipped with a 50 m Chrompack CP-Sil 8 CB low-bleed MS (5% phenyl methyl silicone) analytical column (i.d. 0.25 mm, 0.12 µm film thickness). The column was directly connected to the detector and to the thermal desorber. The GC oven program was 35-280 °C at 5 °C/min and 16 min at 280 °C. The mass spectrometers were a Kratos Profile double focusing sector instrument (scan rate 0.4 per s, mass range m/z 29-432) and a Perkin-Elmer Turbomass (scan rate 0.5 per s, mass range m/z 30-400). Criteria for positive qualitative identification was manual inspection of each mass spectrum combined with library search (Wiley) and retention time identification with an authentic standard within tR ( 0.03 min. VOL. 36, NO. 19, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Sample Matrix with Experimental Conditions gas type NO2a NO2b blanka blankb NOa NOb OHa OHb H2O2a H2O2b blanka blankb O3a O3b blanka blankb limonene-O3a limonene-O3b blanka blankb
sample vol. (L)
no. of samples
concn (ppb)
RH %
5 9 20 20 5 9 20 144 20 336, 532 570 397 20 2 20 5 20 20 20 5
3 1 1 1 3 1 3 1 3 2 3 1 3 2 1 1 5 1 1 1
1400 1400 0 0 1400 1400 unknownc unknownc 23000 46000 0 0 50 1000 0 0 1700/203d 1700/203d 0 0
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