Analysis of Pesticide Residues in Spinach using Phenomenex roQ™ QuEChERS AOAC Kits by LC/MS/MS and GC/MS

Importance of the Topic

Pesticide residue analysis in leafy vegetables is critical for ensuring food safety and meeting regulatory limits. Spinach poses particular challenges due to its high pigmentation and nutrient content, which can interfere with detection of low-level contaminants. A robust, efficient cleanup and detection strategy helps protect consumer health and comply with international standards.

Objectives and Study Overview

This work evaluates the AOAC Official Method 2007.01 for simultaneous determination of 18 pesticides and two internal standards in spinach extracts. Phenomenex roQ QuEChERS extraction and PSA/GCB dispersive SPE kits were used for sample cleanup. Extracts were split and analyzed by LC/MS/MS and GC/MS to assess recovery, reproducibility, and sensitivity against maximum residue limits.

Methodology and Sample Preparation

Spinach was flash frozen, homogenized under liquid nitrogen, and 15 g portions were spiked at two levels. Extraction employed acetonitrile containing 1% acetic acid and a pre-measured salt packet (MgSO₄ and sodium acetate). After mixing and centrifugation, 8 mL of supernatant underwent dSPE with MgSO₄, PSA, and graphitized carbon black to remove moisture, fatty acids, and pigments. Final extracts were evaporated and reconstituted separately for LC/MS/MS and GC/MS analysis.

Instrumentation Used

• LC/MS/MS system: Agilent 1200 HPLC with Luna C18(2) 3 µm column coupled to an AB SCIEX API 4000 triple quadrupole via electrospray ionization.
• GC/MS system: Agilent 6890N gas chromatograph with 5973 mass spectrometer and Zebron ZB-5MSi capillary column.

Main Results and Discussion

Recoveries for most target compounds fell between 70 % and 120 % with RSDs below 15 %, in line with AOAC criteria. Highly planar pesticides (e.g., chlorothalonil, thiabendazole) exhibited reduced recoveries due to stronger adsorption onto carbon black. Chromatographic separation was well resolved in both LC and GC methods, and adjustments to the injection solvent prevented early-eluting peak distortion.

Benefits and Practical Applications

The roQ QuEChERS approach with pre-packaged kits streamlines sample preparation, reduces solvent use, and ensures consistent cleanup across batches. Effective pigment removal and broad analyte coverage make it well suited for routine quality control and regulatory laboratories.

Future Trends and Applications

Future developments may expand the method to additional pesticide classes and food matrices, incorporate high-resolution mass spectrometry for improved selectivity, optimize sorbent blends to minimize loss of planar analytes, and implement automation for higher throughput testing.

Conclusion

The Phenomenex roQ QuEChERS extraction combined with PSA/GCB cleanup and dual LC/MS/MS and GC/MS analysis delivers accurate, reproducible quantification of multiple pesticide residues in spinach. The protocol meets official validation requirements while offering a practical workflow for laboratories.

References

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