Automated Disposable Pipette Extraction of Pesticides from Fruits and Vegetables

Significance of the Topic

Routine and accurate detection of pesticide residues in fruits and vegetables is essential to ensure food safety and compliance with regulatory limits.
The sample preparation step often represents the bottleneck in pesticide analysis due to time consumption and solvent use.
Disposable Pipette Extraction (DPX) offers a streamlined approach that reduces solvent consumption, accelerates workflows, and supports full automation for high-throughput laboratories.

Objectives and Study Overview

The study demonstrates the integration of DPX with an automated GERSTEL MultiPurpose Sampler (MPS2) for the extraction of diverse pesticide classes from produce.
Key goals include comparing DPX with the QuEChERS method, evaluating recovery and reproducibility, and assessing the suitability of DPX eluents for direct injection into gas chromatography–mass spectrometry (GC–MS).

Methodology

DPX combines dispersive solid-phase extraction within a pipette tip containing a small amount of sorbent.
Sample Preparation

• Blend fruit or vegetable sample with acetonitrile and salt following an adapted QuEChERS protocol.
• Filter the extract and adjust the aqueous content for DPX operation.

Manual DPX

• Mix the acetonitrile extract with water and salt inside the DPX tip by aspirating air–liquid cycles.
• Wash sorbent with water, then elute analytes with minimal volume of hexane–ethyl acetate.

Automated DPX

• Use GERSTEL MPS2 to perform repeated aspirate–mix–dispense cycles with 1 mL DPX tips.
• Execute washing and elution steps in sequence, delivering approximately 0.25 mL of organic solvent as final eluate.
• Add an external standard to compensate for volume variation before GC–MS analysis.

Instrumentation Used

• GERSTEL MPS2 autosampler for DPX extraction and direct sample introduction.
• Agilent 6890N gas chromatograph coupled to a 5975 Inert XL mass selective detector.
• DB-17MS capillary column (30 m × 0.25 mm, 0.25 µm film).

Key Results and Discussion

DPX achieved recoveries near 90–110 % with relative standard deviations below 5 % for a wide range of organochlorine pesticides, including BHC isomers, endosulfan, and DDT derivatives.
Organophosphate pesticides also showed strong performance, though highly polar analytes such as dichlorvos and mevinphos displayed lower recoveries.
Linear calibration (R2 > 0.995) was demonstrated across multiple matrices at concentrations from 0.1 to 2.0 ppm.
Extracts remained sufficiently clean for direct GC–MS injection without centrifugation or solvent evaporation, highlighting DPX as a greener alternative.

Benefits and Practical Applications

• Significant reduction in solvent consumption and elimination of evaporation steps.
• Rapid extraction cycles compatible with full automation.
• Consistent and high recoveries across diverse pesticide classes.
• Direct injection of eluents streamlines workflow, reducing hands-on time.

Future Trends and Opportunities

Combining DPX with large-volume injection techniques in programmable temperature vaporizing inlets can further enhance sensitivity for trace-level analysis.
Development of mixed-mode DPX sorbents, such as polar or ion-exchange materials, may improve recoveries of highly polar pesticides.
Integration with other sample preparation strategies, such as QuEChERS-based cleanup tips, can broaden the scope of analytes and matrices.

Conclusion

Disposable Pipette Extraction represents a rapid, efficient, and environmentally friendly approach for pesticide residue analysis in fruits and vegetables.
The method supports full automation, high throughput, and direct compatibility with GC–MS, offering a robust alternative to traditional SPE and QuEChERS workflows.

References

• Anastassiades, M.; Lehotay, S. J.; Stajnbaher, D.; Schenck, F. J. J. AOAC Int. 2003, 86, 412.
• Lehotay, S. J. J. AOAC Int. 2007, 90, 485.