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Optimization of Time-Weighted Average Air Sampling by Solid-Phase Microextraction Fibers Using Finite Element

Bulat Kenessov1, Jacek A Koziel2, Nassiba Baimatova3

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Accurate time-weighted average (TWA) air sampling for volatile organic compounds (VOCs) using solid-phase microextraction (SPME) was improved by modeling diffusion and optimizing fiber retraction depth. This enhances VOC analysis accuracy and detection limits.

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Area of Science:

  • Analytical Chemistry
  • Environmental Science
  • Chemical Engineering

Background:

  • Solid-phase microextraction (SPME) offers advantages for air sampling of volatile organic compounds (VOCs).
  • However, achieving high accuracy in time-weighted average (TWA) VOC concentration determination with SPME, especially over longer sampling periods, remains a challenge.
  • Existing experimental methods to identify and resolve accuracy issues are often hindered by high uncertainties and practical limitations.

Purpose of the Study:

  • To develop a predictive model for the TWA extraction process in SPME air sampling.
  • To optimize TWA air sampling methodologies using SPME through computational modeling.
  • To investigate and mitigate factors limiting accuracy in SPME-based VOC monitoring.

Main Methods:

  • Utilized finite element analysis software (COMSOL Multiphysics) to model the TWA extraction dynamics of VOCs using SPME.
  • Investigated the impact of slow analyte diffusion within porous SPME coatings and analyte concentration changes near the fiber tip on sampling rates.
  • Evaluated the effect of increased fiber retraction depth (Z) and alternative SPME liner configurations on sampling recovery and accuracy.

Main Results:

  • Identified slow diffusion within porous coatings and analyte concentration equilibration near the fiber tip as key factors reducing sampling rates.
  • Demonstrated that increasing fiber retraction depth (Z) to the maximum (40 mm) with a Carboxen/polydimethylsiloxane (Car/PDMS) fiber significantly improved VOC recovery and accuracy.
  • An alternative SPME liner configuration (78.5 × 0.75 mm ID) achieved comparable accuracy with enhanced detection limits, with potential for further improvement via diameter modification.

Conclusions:

  • The developed finite element model accurately describes TWA VOC extraction by SPME, revealing critical performance limitations.
  • Optimized sampling parameters, including increased fiber retraction depth and modified liner designs, lead to more accurate TWA VOC measurements.
  • The model and findings provide a foundation for developing improved analytical methods for TWA VOC determination and can be applied to other sampling matrices.