Impact of water/PDMS phase ratio, volume of PDMS, and sampling time on Stir Bar Sorptive Extraction (SBSE) recovery of some pesticides with different KO/W

In Stir Bar Sorptive Extraction (SBSE) organic analytes are enriched from aqueous samples by sorption onto a thick film of polydimethylsiloxane (PDMS) coated on a glass-enveloped magnet. Sampled analytes are recovered by thermodesorption (TDS) and analysed on-line by cGC-MS. This study evaluates the SBSE recovery as a function of K-O/W, the phase ratio (beta), PDMS volume (20, 40, and 110 muL), sample volumes (4, 10, 100, and 1000 mL), and sampling time (0.67, 1, 2, 4, 5, 6, and 24 h) for three pesticides with different K-O/W [parathion methyl (K-O/W: 7.24 x 10(2)), beta-endosulfan (K-O/W: 6.8 x 10(3)), and buprofezin (K-O/W: 2.0 x 10(4))]. Experimental recoveries with SBSE in reasonable sampling times were found to be mainly conditioned by beta, which must be as low as possible either by operating on small sample volumes or by using stir bars coated with high PDMS volume when samples of relatively large volume are analysed.