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)

Significance of the Topic

Monitoring pesticide residues in environmental waters and consumables is critical due to their potential health risks, persistence, and bioaccumulation. Solvent-less sorptive techniques like stir bar sorptive extraction (SBSE) coupled with fast GC/MS using a modular accelerated column heater (MACH) enable high sensitivity and rapid multi-residue screening. Applying a dual SBSE strategy further expands the polarity range covered.

Objectives and Study Overview

This work describes the development and validation of a fast screening method for 82 pesticide residues (organochlorine, carbamate, organophosphorus, pyrethroid, and others) in aqueous samples. The approach employs dual SBSE under different extraction conditions, followed by thermal desorption and fast GC/MS analysis to achieve ng/L detection limits.

Methodology and Instrumentation

• Dual SBSE: simultaneous extraction of two 20 mL samples with 30% NaCl and without modifier at 24 °C for 60 min using polydimethylsiloxane-coated stir bars.
• Thermal Desorption: GERSTEL TDU desorption at 40–280 °C, cryo-focusing in a PTV inlet.
• Fast GC/MS: Agilent 6890N GC with MACH heater and 10 m×0.18 mm DB-5 column; quadrupole MSD in scan mode (m/z 58–510).
• Instrumentation: GERSTEL Twister® stir bars, TDU, MPS2 autosampler, CIS4 inlet, MACH module, Agilent 5975 MSD.

Key Results and Discussion

• Linearity (r²>0.990) for 69 pesticides over 25–1000 ng/L; LODs of 0.58–10 ng/L for most analytes.
• Absolute recoveries of 11–72% with RSD<15% (n=6) across log Kow 1.7–8.35.
• Salt addition (30% NaCl) improved extraction of hydrophilic pesticides (log Kow<3.5) but reduced hydrophobic analytes.
• Dual SBSE compensated for hydrophobic losses, yielding uniform enrichment across polarity ranges.
• Application examples: river water contained fenobucarb (16 ng/L) and diazinon (4.9 ng/L); brewed green tea showed pirimiphos-methyl (10 ng/L) and tebuconazole (240 ng/L).

Contributions and Practical Applications

This method offers a fast, solvent-free platform for trace-level pesticide monitoring in water and beverage samples, with minimal sample preparation and high throughput, ideal for environmental surveillance and food safety laboratories.

Future Trends and Potential Applications

• Automation of dual SBSE for continuous monitoring.
• Adaptation to other contaminants and complex matrices.
• Advances in stir bar coatings and ultra-fast GC for lower LODs and shorter cycle times.

Conclusion

Dual SBSE combined with TD and MACH-based fast GC/MS provides a robust, sensitive, and rapid analytical workflow for multi-residue pesticide analysis in aqueous samples, enabling ng/L detection across a broad polarity spectrum without extensive sample prep.

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