24 h diffusive sampling of toxic VOCs in air onto Carbopack X solid adsorbent followed by thermal desorption/GC/MS analysis—laboratory studies

Abstract

Diffusive sampling of a mixture of 42 volatile organic compounds (VOCs) in humidified, purified air onto the solid adsorbent Carbopack X was evaluated under controlled laboratory conditions. The evaluation included variations in sample air temperature, relative humidity and ozone concentration. Linearity of samples with loading was examined both for a constant concentration with time varied up to 24 h and for different concentrations over 24 h. Reverse diffusion and its increase with accumulation of sample were determined for all compounds. Tubes were examined for blank levels, change of blanks with storage time, and variability of blanks. Method detection limits were determined based on seven replicate samples. Based on this evaluation, 27 VOCs were selected for quantitative monitoring in the concentration range from approximately 0.1 to 4 ppbv. Comparison results of active and diffusive samples taken over 24 h and under the same simulated ambient conditions at a constant 2 ppbv were interpreted to estimate the effective diffusive sampling rates (ml min(-1)) and their uncertainties and to calculate the corresponding diffusive uptake rates (ng ppmv(-1) min(-1)).

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

“…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 O 3 exposure, and exploring some of the potentially causative mechanisms. Two relatively new materials are evaluated: Carbopack B, which has not been tested previously for O 3 artifacts, and Carbopack X, which has been examined recently by McClenny et al 7 O 3 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 O 3 -adsorbent artifacts and for each of the four adsorbents.…”

“…6 Small negative biases have been noted for 1,1,2-trichloroethane and 3-chloropropene (of 27 compounds tested) in preloaded Carbopack X tubes exposed to O 3 in diffusive sampling. 7 Benzaldehyde, phenol, and acetophenone have been identified as positive artifacts resulting from O 3 -GCB exposure ( …”

“…3,[5][6][7][8] The most recognized and significant interference occurs because of reactions with O 3 . 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.…”

Diffusive Uptake Rates of Volatile Organic Compounds on Standard ATD Tubes for Environmental and Workplace Applications

“…Some available UR datasets using ATD tubes include: (1) 24-h URs on Carbopack X solid sorbent for 27 VOCs determined in laboratory chamber [16]; (2) 4-day URs on Tenax TA and Carbopack B for 10 VOCs determined in laboratory chamber [37]; and (3) 4-to 10-day URs on Carbopack B for 68 VOCs determined by field tests [38]. Depending on the analyte/sorbent combination, the adsorption behavior might be completely different and new models should be developed.…”

“…ATD tubes offer the greatest flexibility for users to select sorbents and determine tube configuration but at the same time, add complexity to the UR determination. Many studies have determined URs from the diffusion theory [12], in laboratory chambers [13][14][15][16] and by comparing active and passive sampling in the field [17,18]. Many factors influence URs, including sorbent selection, tube configuration, exposure duration and environmental conditions.…”