Nonequilbrium quantitation of volatiles in air streams by solid-phase microextraction

Area of Science:

• Analytical Chemistry
• Environmental Science
• Physical Chemistry

Background:

• Solid-phase microextraction (SPME) is widely used for analyzing airborne organic compounds.
• Accurate quantitation typically requires SPME fiber equilibration, which is often unachievable for heavier compounds within practical timeframes.
• This limitation restricts the scope of SPME for certain analytes and sampling durations.

Purpose of the Study:

• To develop a method for quantitating airborne organic compounds using SPME during the non-equilibrium phase.
• To investigate the kinetics of SPME extraction for various organic compounds (alkanes, alcohols, esters) using poly(dimethylsiloxane) fibers.
• To establish a practical quantitation formula applicable even when full equilibrium is not reached.

Main Methods:

• Studied SPME kinetics for alkanes (C9-C22), alcohols (C6-C13), and methyl esters (C6-C16) from air streams with constant analyte concentrations.
• Collected over 1900 data points varying sampling time (30 min to 3 days), temperature, fiber coating thickness, air flow rate, and tubing diameter.
• Developed and validated a new kinetic equation using nonlinear regression, linking analyte properties and sampling conditions to extraction kinetics.

Main Results:

• A simple kinetic equation accurately described SPME extraction data, showing an explicit relationship between fiber sensitivity and equilibration time.
• The derived regression equation successfully linked analyte properties (functional group, GC retention index) and sampling conditions to the extraction process.
• The model allows direct calculation of absolute analyte concentration from extracted amounts, irrespective of equilibrium status, with a residual variability of 9.4%.

Conclusions:

• The developed kinetic model overcomes the limitation of requiring full equilibration in SPME analysis of airborne compounds.
• This approach enables accurate quantitation of a wider range of organic compounds, including heavier ones, under various sampling conditions.
• The study provides new fiber calibration data and practical insights for optimizing SPME sampling from air.