Fast Screening of Pesticide Multiresidues in Aqueous Samples by Dual Stir Bar Sorptive Extraction (Dual SBSE) and Thermal Desorption – Fast GC/MS using a Modular Accelerated Column Heater (MACH)

A method for fast screening of pesticide multiresidues in aqueous samples using dual stir bar sorptive extraction (dual SBSE) – thermal desorption (TD) – fast GC/MS has been developed. Recovery of 82 pesticides – organochlorine, carbamate, organophosphorous, pyrethroid and others – for the SBSE was evaluated as a function of octanolwater distribution coeffi cients (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 were placed in a single glass desorption liner and were simultaneously desorbed. The desorbed compounds were analyzed by fast GC/MS using a modular accelerated column heater (MACH). The method showed good linearity (r2 > 0.9900) and high sensitivity (limit of detection: < 10 ng/L) for most of the target pesticides. The method was applied to the determination of pesticides at ng/L levels in river water and brewed green tea.