Deactivated fused silica tubing: A solution for flexible time weighted averaging needle trap sampling

In time-weighted averaging (TWA) with needle trap extraction (NTE), the control of the sampling rate is critical for accurate analysis. By adjusting the diffusion length and cross-sectional area, the sampling rate can be modified in accordance with Fick's first law of diffusion. In this study, deactivated fused silica tubing (DFST) of varying lengths was used to fine-tune these parameters, allowing for precise control of the sampling rate in TWA-NTE devices. The fabricated devices were used to extract benzene, toluene, ethylbenzene, o-xylene (BTEX), and selected alkanes as model compounds. Experimental sampling rates were obtained using a standard gas flow generating system and compared to theoretical values, showing statistical similarity. The devices were tested in various real-world environments, including a parking lot, garages, and a box containing a burning candle, and their practical applicability was confirmed. The use of DFST effectively controlled both diffusion length and cross-sectional area, thereby enhancing sampling performance. The results of this study demonstrate that DFST serves as a versatile and adjustable attachment for needle trap devices (NTD), significantly broadening the range of NTD applications in terms of concentration and sampling time. This approach not only reduces analysis costs but also improves adherence to Fick's law by minimizing the influence of other mass transfer mechanisms. Consequently, more consistent and predictable extraction behavior was observed, particularly for higher molecular weight species, strengthening the overall applicability of the TWA-NTE method.