Geometry-optimized passive SPME sampler for time-weighted average determination of volatile organic compounds in air:
Olga P Ibragimova1, Anara Omarova1, Diana Sovetova1
1Center of Physical Chemical Methods of Research and Analysis, Faculty of Chemistry and Chemical Technology, Farabi University, Almaty, 050012, Kazakhstan; Environmental and Analytical Chemistry Laboratory, Farabi University, Almaty, 050038, Kazakhstan.
Abstract:
Accurate time-weighted average (TWA) concentrations are critical for evaluating inhalation exposure, health risks, and pollution trends. Solid-phase microextraction (SPME) offers a sensitive, simple alternative to conventional volatile organic compound (VOC) monitoring methods. Using a gas chromatograph inlet liner as a passive sampler with an internally exposed SPME fiber eliminates analyte adsorption onto the metallic surface, a limitation of retracted-fiber configurations. Based on COMSOL Multiphysics modeling results, a modified sampler was fabricated with an enlarged extraction zone (0.80 mm) and reduced diffusion-path zone (0.34 mm). The 85-μm Car/PDMS fiber was the optimal coating. Corroborating numerical simulations, the modified sampler at 67 mm diffusion path length (Z) with Car/PDMS (91-111%) and MOF-199 (80-94%) fibers achieved higher recoveries than the standard GC liner for all VOCs except perchloroethylene (PCE, 121-145%) and acetophenone (ACP) on MOF-199 (<14%). Extracted mass increased linearly with 1/Z (R2 > 0.95, except ACP); Z = 67 mm was selected as optimal, whereas longer paths (97-127 mm) caused overestimation and higher variability for most analytes. Combined kinetic and diffusion-path analyses indicated analyte-dependent responses consistent with coupled gas-phase transport, coating uptake, and sorption effects. The available data did not permit identification of a single rate-controlling mechanism. The method demonstrated exceptional linearity (R2 > 0.99), intra-day repeatability (RSD≤14%), inter-day reproducibility (RSD≤23%), spike recoveries of 87-105% (PCE, 123%), and detection/quantification limits of 0.03-0.59 and 0.10-1.99 μg/m3, respectively. During seven 24-h sampling events (March, 2023) in Almaty, Kazakhstan, TWA VOC concentrations were 0.85-38.4 μg/m3. Daily benzene levels remained below Kazakhstan's 24-h limit (100 μg/m3) but exceeded Israel's stricter limit (3.9 μg/m3) by 1.2- to 5-fold on 6 of 7 days.
