Uptake rate behavior of tube-type passive samplers for volatile organic compounds under controlled atmospheric conditions

A systematic laboratory research was performed to investigate the diffusive uptake of four target compounds (limonene, toluene, ethyl acetate, hexane) on axial-sampling sorbent tubes filled with Tenax TA. In a controlled atmosphere (temperature: 21.0 ± 1.8 °C; relative humidity set at different values between 5 and 80%), these passive samplers were exposed for 1, 3 and 7 days to a constant target compound concentration between 8 and 85 ppbv. Simultaneous active sampling and TD-GC-MS analysis was performed to determine VOCs concentrations. A power-law relationship between the sorbed mass on the sampler and exposure dose (11–179 ppmv min) was observed for all compounds. Compounds with a lower Tenax to air partitioning coefficient, i.e. with a lower affinity for Tenax showed a larger deviation from the expected linear relationship, assuming theoretical sampling rates on an ideal sorbent. Results showed that experimentally determined uptake rates (0.90–2.12 ng (ppmv min)−1) may be up to a factor of 2 lower than the theoretical ideal sampling rates, calculated from the molecular diffusion coefficients and the geometrical parameters of the sampler. The applicability of internal standard calibration for passive sampling was evaluated and a practical methodology is proposed with ethylbenzene-d10 as an internal standard.