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 Ko/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 Ko/w (log Ko/w < 3.5) and another extraction with unmodified sample solution is targeting solutes with medium and high Ko/w (log Ko/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 °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 (r2 > 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.