Comparison of thin-film microextraction and stir bar sorptive extraction for the analysis of polycyclic aromatic hydrocarbons in aqueous samples with controlled agitation conditions

The characterization of a poly(dimethylsiloxane) (PDMS) thin film for active extraction of some polycyclic aromatic hydrocarbons was investigated in both a 1-L aqueous solution and a flow-through system. The thin film was attached to an electric bench-drill at a constant rotation speed for constant agitation and fast extraction. The performance of a PDMS-coated stir bar at a constant stirring speed was also investigated. The comparison showed that the extraction rate was much higher when using the thin film than the stir bar, and that the equilibration time was greatly shortened due to the larger surface area/volume ratio of the thin film. The extraction rate was roughly proportional to surface area of the extraction phase during the initial stage of the extraction process; the amount of analyte extracted was proportional to the ratio of the extraction phase between the thin film and the stir bar. Different agitation and stirring rates of the thin film and stir bar were applied for extraction, revealing that extraction efficiency can be improved by increasing rotation rate. The application of rotated thin film in the field proved it is a valid and easily operated method for the determination of polycyclic aromatic hydrocarbons (PAHs) in a campus river. However, the stir bar is not as convenient as a thin film in field sampling.