Analysis of Pesticide Residues in Spinach Using AOAC Pigmented dSPE with Carbon S Cleanup and LC/MS/MS

Significance of the Topic

Photochemical analysis of pesticide residues in leafy vegetables is crucial for consumer safety and regulatory compliance. Co-extracted pigments like chlorophyll can cause matrix effects, reduce sensitivity, and contaminate LC/MS/MS systems. Implementing efficient cleanup steps enhances accuracy, reproducibility, and instrument robustness.

Goals and Overview

This study evaluated the Agilent Bond Elut QuEChERS AOAC Pigmented Fruits and Vegetables dSPE kit with advanced Carbon S sorbent for analyzing 26 pesticide residues in fresh organic spinach by LC/MS/MS. Performance was benchmarked against the traditional kit with graphitized carbon black (GCB), and both 2 mL and 15 mL formats of the Carbon S kit were assessed for consistency.

Methodology and Instrumentation

• Sample Preparation: 15 g spinach homogenate extracted using QuEChERS AOAC protocol with acetonitrile (1% acetic acid), followed by dSPE cleanup with Carbon S or GCB sorbents.
• Cleanup Formats: 2 mL and 15 mL dSPE tubes with equivalent Carbon S ratios; final dilution to 20:80 ACN/water.
• Instrumentation: Agilent 1260 Infinity II LC system with ZORBAX RRHD Eclipse Plus C18 column, coupled to Agilent Ultivo triple quadrupole LC/MS with Jet Stream ESI source.
• MRM Parameters: Optimized for 26 pesticides in positive ion mode, using targeted dMRM transitions.

Main Results and Discussion

• Recoveries: Carbon S cleanup yielded average recoveries >80% (40–97%) for 26 pesticides, outperforming GCB (64% average, 9–106%). Significant improvements were observed for planar compounds such as pymetrozine and carbendazim.
• Reproducibility: RSDs <20% across all targets; both 2 mL and 15 mL formats showed consistent recoveries (80–81% average) and <15% RSD.
• Pigment Removal: Carbon S sorbent achieved >95% chlorophyll removal in spinach, comparable to GCB.
• Validation: Calibration linearity R2 >0.99 for most analytes, accuracy ranging from 35% to 110% at 10 and 100 ng/g spiked levels; RSDs <16%.

Benefits and Practical Applications

• Enhanced quantification of challenging planar pesticides with reduced signal suppression.
• Direct replacement of GCB-based cleanup with minimal method adaptation.
• Improved instrument cleanliness and reduced maintenance due to efficient pigment removal.
• Suitable for routine QA/QC and regulatory monitoring of leafy vegetables.

Future Trends and Opportunities

Integration of hybrid carbon sorbents in automated, high-throughput protocols and passthrough cleanup formats may further streamline multiclass pesticide analysis. Expanding the approach to diverse matrices and adopting advanced MS technologies will continue to improve sensitivity and sample throughput.

Conclusion

The Agilent Bond Elut QuEChERS AOAC pigmented dSPE kit with Carbon S delivers equivalent pigment removal to GCB while significantly enhancing recoveries and reproducibility for a broad range of pesticides in spinach. Both 2 mL and 15 mL formats are validated for robust LC/MS/MS analysis and serve as direct replacements for traditional cleanup methods.

Reference

• Zhao, L.; Wei, T. Determination of Multiclass, Multiresidue Pesticides in Spring Leaf Mix by Captiva EMR–HCF Passthrough Cleanup and LC/MS/MS; Agilent Technologies Application Note 5994-4765EN, 2022.