Analyzing Pesticide Residues in Lettuce by the EN 15662 Method using Phenomenex roQ™ QuEChERS Kits Followed by LC/MS/MS and GC/MS Analysis

Significance of the Topic

Leafy greens such as lettuce are consumed worldwide and are prone to pesticide contamination. Reliable multi-residue analysis is essential to protect public health, comply with international maximum residue limits (MRLs) and support regulatory monitoring programs.

Study Objectives and Overview

This work evaluates the European Standard EN 15662 QuEChERS approach using Phenomenex roQ™ Extraction and roQ™ dSPE Kits for the determination of 25 pesticides and two internal standards in lettuce. After extraction and cleanup, samples were analyzed by both LC/MS/MS and GC/MS to demonstrate comprehensive detection and quantification below regulatory limits.

Methodology and Instrumentation

Sample preparation and analytical workflow:

• Frozen lettuce was homogenized under liquid nitrogen to a fine powder.
• 10 g of sample was mixed with 10 mL acetonitrile and internal standards, then salted out using a pre-weighed packet of MgSO₄, NaCl and citrate buffers (roQ Extraction Kit).
• After centrifugation, 6 mL of supernatant was cleaned up in roQ dSPE tubes containing MgSO₄ and PSA; graphitized carbon black (GCB) may be added for pigmented matrices.
• Extracts were split: 250 µL aliquots were evaporated and reconstituted in aqueous methanol for LC/MS/MS; 2.25 mL aliquots were solvent-exchanged to toluene for GC/MS.

Instrumentation:

• LC/MS/MS: Agilent 1200 LC with Luna® C18(2) 150×3.0 mm column (3 µm), gradient elution with 5 mM formic acid in water/methanol, detection on an AB SCIEX API 4000 triple quadrupole in positive ESI.
• GC/MS: Agilent 6890 GC coupled to 5973 MS with Zebron™ ZB-5MSi Guardian™ 30 m×0.25 mm×0.25 µm column, helium carrier, temperature ramp to 340 °C, splitless injection.

Main Results and Discussion

Recovery and precision:

• Most pesticides showed recoveries of 70–120 % with RSDs < 15 % at spiking levels of 80 and 200 ng/g.
• Acid-labile compounds such as pymetrozine exhibited lower recoveries, consistent with EN 15662 reports.
• Combining LC/MS/MS and GC/MS extended analyte coverage across polar, semi-polar and non-polar classes.

The roQ kits’ pre-weighed salts, leak-free tubes and streamlined workflow reduced handling errors and improved throughput. Effective removal of water, fatty acids and pigments minimized matrix effects, protecting column lifetime and enhancing sensitivity.

Benefits and Practical Applications

The described method offers:

• A rapid, cost-effective multisource extraction and cleanup using standardized consumables.
• High throughput suitable for routine QA/QC laboratories.
• Regulatory compliance through robust performance below MRLs.
• Flexibility to adapt sorbent combinations (PSA, C18-E, GCB) for diverse matrices.

Future Trends and Potential Applications

Emerging directions include:

• Integration of high-resolution mass spectrometry for non-targeted screening.
• Automation and miniaturization of QuEChERS workflows to reduce solvent and sample volumes.
• Development of novel sorbent materials for enhanced cleanup of challenging matrices.
• Application of this protocol to a broader range of fruits, vegetables and processed foods.

Conclusion

The EN 15662 QuEChERS method with Phenomenex roQ™ kits delivers reliable, reproducible multi-residue pesticide analysis in lettuce. It fulfills international performance criteria, streamlines sample preparation and supports comprehensive LC/MS/MS and GC/MS detection.

References

1. Lehotay SJ, de Kok A, Hiemstra M, van Bodegraven P. Validation of a fast and easy method for residues of 229 pesticides in fruits and vegetables. J AOAC Int. 2005;88(2):595–614.
2. EN 15662:2018 European Committee for Standardization. Foods of plant origin—Determination of pesticide residues using GC- and LC-MS/MS following acetonitrile extraction/partitioning and cleanup by dispersive SPE (QuEChERS method).
3. FDA. Pesticide Residue Monitoring Program. U.S. Food and Drug Administration website.