Airflow rate in the quantitation of volatiles in air streams by solid-phase microextraction

A previously reported method for nonequilibrium quantitation of air-borne volatiles from air streams by solid-phase microextraction (SPME) was improved by broadening its scope. The original method was defined for the 100-microm poly(dimethylsiloxane) fiber type for a wide range of analytes, sampling temperatures, and sampling times, but only for four specific airflow configurations. The present study extends the choice of volumetric airflow rates to a continuous range between 2 and 220 mL/min. Kinetics of absorption was characterized for 21 different airflow rates within this range using n-alkanes of 11-18 carbons. Nonlinear regression analysis was used to develop a relationship between airflow rate and absorption kinetics and then to integrate these results into the previous model. The overall model (with 8 fitted degrees of freedom and based on 2240 measurements) had an r2 value of 0.9972 and residual variability (RSD) of 9.75%, which compared favorably with the sampling precision of SPME (approximately 5%). The method allows absolute quantitation by SPME for a broad range of analytes and sampling parameters without prior calibration of the individual fiber and regardless of whether equilibration is complete. Simulations are presented that demonstrate how the choice of airflow rate can affect quantitation.