Fast screening of pesticide multiresidues in aqueous samples by dual stir bar sorptive extraction-thermal desorption-low thermal mass gas chromatography-mass spectrometry

A method for fast screening of pesticide multiresidues in aqueous samples using dual stir bar sorptive extraction-thermal desorption-low thermal mass gas chromatography-mass spectrometry (dual SBSE-TD-LTM-GC-MS) has been developed. Recovery of 82 pesticides-organochlorine, carbamate, organophosphorous, pyrethroid and others-for the SBSE was evaluated as a function of octanol-water distribution coefficients (log K-o/w: 1.7-8.35), sample volume (2-20 mL), salt addition (0-30% NaCl), and methanol addition (0-20%). The optimized method consists of a dual SBSE performed simultaneously on respectively a 20-mL sample containing 30% NaCl and a 20-mL sample without modifier (100% sample solution). One extraction with 30% NaCl is mainly targeting solutes with low K-o/w, (log K-o/w < 3.5) and another extraction with unmodified sample solution is targeting solutes with medium and high K-o/w (log K-o/w > 3.5). After extraction, the two stir bars are placed in a single glass desorption liner and are simultaneously desorbed. The desorbed compounds are analyzed by use of LTM-GC-MS with fast temperature programming (75 degrees C min(-1)) using a 0.18 mm i.d. narrow-bore capillary column and fast scanning (10.83 scan s(-1)) using quadrupole MS. The method showed good linearity (r(2) > 0.9900) and high sensitivity (limit of detection: < 10 ng L-1) for most of the target pesticides. The method was applied to the determination of pesticides at nanograms per liter levels in river water and brewed green tea. (c) 2006 Elsevier B.V. All rights reserved.