Determination of Pesticide Residues in Cucumber Using GC-MS/MS With APGC™ After Extraction and Clean-up Using QuEChERS

Importance of the Topic

Reliable, high-throughput methods for detecting trace levels of pesticide residues are essential for food safety, regulatory compliance, and trade. Cucumber, as a widely consumed vegetable, must be monitored to ensure that its pesticide residues do not exceed maximum residue limits (MRLs). The combination of QuEChERS sample preparation with advanced GC-MS/MS using atmospheric pressure gas chromatography (APGC) offers enhanced sensitivity and selectivity, enabling quantitation well below typical MRLs and improving laboratory efficiency.

Aims and Overview of the Study

This work describes the development and validation of a comprehensive multiresidue method for over 200 GC-amenable pesticides in cucumber. Key objectives included:

• Implementing a QuEChERS extraction with dispersive solid-phase clean-up.
• Integrating APGC on a Xevo TQ-XS GC-MS/MS platform to enhance ionization performance.
• Validating method performance against SANTE guidelines, targeting detection limits down to 0.0005 mg/kg.

Methodology and Instrumentation

Sample Preparation:

• Cucumber samples homogenized and spiked with a multiresidue pesticide standard.
• Extraction via CEN QuEChERS protocol using acetonitrile, salt partitioning, and PSA-based dispersive SPE.
• Matrix-matched calibration standards prepared from 0.0005 to 0.10 mg/kg.

GC-MS/MS Conditions:

• Agilent 7890A GC with CTC CombiPal autosampler, Restek Rxi-5Sil MS column.
• Splitless injection (1 µL acetonitrile extract), pulsed at 32 psi for 1.2 min at 250 °C.
• Helium carrier gas, oven program 90 °C to 330 °C at 8.5 °C/min.

APGC-MS/MS:

• Waters Xevo TQ-XS with APGC 2.0 source, corona current 2.0 µA.
• Source at 150 °C, transfer line 280 °C, nitrogen makeup gas.
• Data acquired in MRM mode using Quanpedia database; processed with TargetLynx XS.

Main Results and Discussion

Sensitivity and LOD:

• All but one of 203 analytes were detected at 0.0005 mg/kg; two compounds were below detection.
• 85% of analytes showed potential for even lower detection limits.

Calibration and Quantification:

• Most analytes exhibited r2>0.99 and residuals within ±20% per SANTE.
• Minor adjustments to LCL (e.g., folpet, op-DDT) yielded acceptable performance.

Accuracy and Repeatability:

• Recovery between 70–120% for 94% of analytes at 0.001 mg/kg; RSDr ≤20% for 99% at the same level.
• At 0.01 mg/kg, >99% of analytes met recovery and repeatability criteria.

Reference Material Evaluation:

• Cucumber puree QC material confirmed method accuracy and repeatability; tolylfluanid recovery lower due to known stability issues.

Benefits and Practical Applications

The method:

• Delivers ultra-low detection limits (typically <0.0005 mg/kg) without solvent exchange or large-volume injection.
• Combines flexibility of APGC ionization with UPLC-MS/MS on the same platform.
• Supports regulatory monitoring, trade compliance, and research requiring broad pesticide screening.

Future Trends and Potential Applications

Advances may include:

• Further miniaturization of sample preparation to boost throughput and reduce solvent use.
• Integration of ion mobility or high-resolution MS for non-targeted screening and confirmation.
• Extension to other commodity types following tailored validation.

Conclusion

This study demonstrates that QuEChERS extraction combined with APGC-MS/MS on the Xevo TQ-XS provides a robust, sensitive, and selective multiresidue method for over 200 pesticides in cucumber. The approach meets SANTE criteria, supports MRL enforcement, and can be adapted to various matrices.

Used Instrumentation

• Agilent 7890A Gas Chromatograph
• CTC CombiPal Autosampler
• Restek Rxi-5Sil MS Column
• Waters Xevo TQ-XS with APGC 2.0 source
• MassLynx v4.2 and TargetLynx XS software

References

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