The Haworth Press Inc.

Ozone Artifacts and Carbonyl Measurements Using Tenax GR, Tenax TA, Carbopack B, and Carbopack X Adsorbents

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Courtesy of The Haworth Press Inc.

INTRODUCTION

Sampling of airborne volatile organic compounds (VOCs) using thermally desorbable solid adsorbents has proven its usefulness in many environmental applications and has become a routine technique1 with compelling advantages over canisters, especially when a large sample volume or sample transport is needed.2 Many adsorbents are available, and users are faced with the difficulty of selecting materials appropriate for specific applications.3 The ideal adsorbent would have the following characteristics: (1) efficient adsorption and desorption of target compounds, potentially including very volatile, semivolatile, polar, and nonpolar compounds; (2) thermal stability; (3) low background levels of contaminants; (4) unaffected by storage; (5) capable of sampling at very low concentrations; (6) uninfluenced by humidity4; (7) high capacity and breakthrough volume; (8) limited back diffusion losses (especially important for passive and low-flow sampling); (9) minimal water uptake; (10) longevity, allowing numerous conditioning/sampling/desorption cycles; and (11) minimal adsorbent-oxidant reactions that yield artifacts. No single adsorbent fulfils all of these requirements and, increasingly, multisorbent tubes are used.

Air constituents like ozone (O3) and nitrogen oxides (NOx) can react with the adsorbent bed and analytes to form unwanted artifacts that can cause positive artifacts, whereas reactions with previously adsorbed compounds on the surface of the adsorbent can cause negative biases. 3,5–8 The most recognized and significant interference occurs because of reactions with O3.5 Although a number of positive artifacts have been documented,9–12 the literature is limited and qualitative, and identifications of many suspected artifacts have not been confirmed. The importance of artifact formation is likely to increase as method detection limits (MDLs) improve and as the number of polar compounds targeted as analytes grows.

This work characterizes O3-adsorbent artifacts for four popular adsorbents (Tenax GR, Tenax TA, Carbopack B, and Carbopack X) using well-controlled laboratory tests. A quantitative assessment of artifacts is provided using certified calibration standards and gas chromatography (GC)/mass spectrometry (MS) analysis, evaluating aging effects that result from repeated O3 exposure, and exploring some of the potentially causative mechanisms. Two relatively new materials are evaluated: Carbopack B, which has not been tested previously for O3 artifacts, and Carbopack X, which has been examined recently by McClenny et al.7 O3 breakthrough curves developed for the four adsorbents provide new information that helps to explain artifact formation. To quantify the artifacts, analytical methods (including calibrations, MDLs, and absorbent recoveries) were developed for the 15 carbonyls identified as O3-adsorbent artifacts and for each of the four adsorbents.

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