Innovative active carbon fibers-based multipurpose thermal desorption tubes for the analysis of volatile organic compounds

Active carbon fibers (ACFs) were evaluated as alternative sorbent materials for thermal desorption (TD) tubes in the analysis of volatile organic compounds (VOCs). Five commercially available ACFs, in both felt and fabric formats, were compared with conventional multi-bed tubes (MBTs) based on granular carbon adsorbents, with a focus on sampling from moisture-rich matrices, such as exhaust gas and exhaled breath. Sampling was conducted under both dry and saturated (100 % relative humidity) conditions using standard gas mixtures containing 39 VOCs from EPA TO-14 and 33 ozone precursors from the Photochemical Assessment Monitoring Station (PAMS) list. TD-gas chromatography-mass spectrometry (TD-GC-MS) was employed for compound analysis, with method parameters adapted for each sorbent type. ACFs demonstrated superior adsorption performances than MBTs, particularly for very volatile compounds (VVOCs) such as Freon-12, chloromethane, vinyl chloride, bromomethane, chloroethane, which are typically poorly retained by conventional TD tubes. ACF-F-20 achieved recovery rates above 80 % for 49 compounds and over 90 % for 37 compounds, even under humid conditions. In storage experiments, while most analytes remained stable for at least 7 days at 4 °C, highly volatile compounds such as chloromethane and bromomethane showed lower recoveries (34.2 % and 45.1 %, respectively). Application of exhaled breath analysis in one exemplary sample from healthy volunteer identified 19 VOCs, with 10 exhibiting significantly higher concentrations when sampled using ACF-T-20b compared to conventional MBTs. Notably, ACF-T-20b enabled enhanced capture of very volatile species, including methanol, propane, methylglyoxal, and hydroxylamine. These results demonstrate the potential of ACFs to improve VVOCs and VOCs sampling in high-humidity environments, broaden the detectable compound range, and reduce analytical cost and complexity in environmental and biomedical applications.