Stir bar sorptive extraction (SBSE) is a solid phase extraction (SPE) method in which the sorbent is a coating of a solid magnetical stir bar. SBSE applies stir bars varying in length from 1 to 4 cm coated with a relatively thick layer (0.3-1 mm) of  polydimethylsiloxane (PDMS) resulting in PDMS volumes varying from 55 ÁL to 220 ÁL. After a certain stirring time, the stir bar is removed from the aqueous sample and thermally desorbed on-line with a gas chromatograph. Due to the much larger volume of the PDMS-phase extraction efficiency is far better than for SPME.