Automated Multi-Residue Pesticide Analysis in Fruits and Vegetables by Disposable Pipette Extraction (DPX) and Gas Chromatography/Mass Spectrometry

Significance of the Topic

This work addresses the growing demand for rapid and reliable monitoring of pesticide residues in fruits and vegetables. Efficient sample cleanup is critical to protect consumer health, meet regulatory limits, and reduce instrument maintenance by minimizing non-volatile matrix buildup.

Objectives and Study Overview

The study introduces an automated Disposable Pipette Extraction (DPX) workflow for cleanup of QuEChERS extracts prior to GC/MS analysis of multi-residue organochlorine and organophosphate pesticides. The goal is to streamline sample preparation, improve recovery, and increase laboratory throughput.

Methodology and Instrumentation

Samples of orange and spinach extracts, prepared by QuEChERS, were cleaned using DPX Q and DPX Qg tips containing loose sorbent and, in the Qg version, graphitized carbon black for pigment removal. The DPX steps were automated on a GERSTEL MPS 2 Robotic Sampler under MAESTRO control. GC/MS analysis was performed on an Agilent 7890 GC with 5975C MSD (PTV inlet, DB-5MS column, He carrier). Key parameters:

• PTV inlet: splitless, 25 °C ramp to 280 °C
• Oven program: 60 °C (1 min), 10 °C/min to 300 °C (3 min)
• Flow: He constant 1.0 mL/min

Main Results and Discussion

DPX-Qg tips effectively removed green chlorophyll and orange pigments from spinach and orange extracts, respectively. Chromatograms showed strong removal of fatty acids and other interferents in the 15–22 min window. Recovery experiments at 20 and 200 ppb spikes yielded:

• Orange extracts: average recoveries 147 % (20 ppb) and 119 % (200 ppb), RSD <10 %
• Spinach extracts: average recoveries 122 % (20 ppb) and 91 % (200 ppb), RSD <10 %

Comparison with and without DPX cleanup demonstrated clear elimination of matrix effects and improved precision.

Benefits and Practical Applications

The automated DPX workflow shortens cleanup to under one minute per sample, minimizes manual centrifugation steps, and protects the GC inlet from non-volatile residues. It integrates seamlessly with high-throughput pesticide screening in food safety and QA/QC laboratories.

Future Trends and Opportunities

Further enhancements may include optimized DPX parameters (aspiration cycles, speeds), incorporation of isotopically labeled internal standards, expansion to LC-MS workflows, and application to diverse matrices such as cereals, nuts, and processed foods. Integration with advanced autosamplers and data processing will support large-scale surveillance programs.

Conclusion

This study validates DPX-QuEChERS cleanup as a robust, fully automated approach for multi-residue pesticide analysis by GC/MS. The method delivers fast sample preparation, high recoveries, low variability, and reduced instrument maintenance, making it well suited for routine food safety testing.

Used Instrumentation

• Gerstel MPS 2 Robotic Sampler with MAESTRO software
• Agilent 7890 GC with 5975C MSD (triple-axis detector)
• Gerstel CIS 4 PTV inlet
• DPX-Q and DPX-Qg 1 mL pipette tips (DPX Labs, LLC)

Reference

Hongxia Guan et al., Automated Multi-Residue Pesticide Analysis in Fruits and Vegetables by DPX and GC/MS, Gerstel AppNote 1/2009