Exceptional Recoveries of Planar Pesticides From Spinach and Fresh Oregano

Importance of the Topic

Determining planar pesticides in leafy matrices is critical for food safety and regulatory compliance. High chlorophyll content in samples like spinach and fresh oregano poses analytical challenges by co-extracting pigments that interfere with gas chromatography-mass spectrometry (GC-MS). An optimized cleanup method that removes pigment while preserving analyte recovery is therefore essential for accurate quantitation of planar pesticide residues.

Objectives and Study Overview

This study evaluated a new QuEChERS sorbent combination, SupelTM QuE Verde, for cleanup of spinach and oregano extracts prior to GC-MS analysis. Key goals included:

• Assessing chlorophyll removal efficiency in high-pigment plant matrices
• Measuring recovery and precision for 12 planar pesticides spiked at 50 ng/mL
• Comparing performance to traditional graphitized carbon black sorbents

Methodology and Instrumentation

Sample Preparation and Cleanup

• Homogenize 10 g of organic spinach or fresh oregano in a 50 mL centrifuge tube
• Add 10 mL acetonitrile and QuEChERS acetate extraction salts; shake and centrifuge
• Transfer 1 mL supernatant to a 2 mL SupelTM QuE Verde cleanup tube; shake and centrifuge
• Collect cleaned extract in amber vial and spike with planar pesticide mix at 50 ng/mL

Instrumental Analysis

• Gas chromatograph equipped with SLB-5ms capillary column (20 m×0.18 mm I.D., 0.18 μm film)
• Oven program: 60 °C (1 min), ramp 8 °C/min to 300 °C, hold 10 min
• Injection: 1 μL splitless, injector at 250 °C, split opened at 0.75 min
• Carrier gas: helium at 0.7 mL/min constant flow
• Mass spectrometer in selected ion monitoring (SIM) mode, interface 325 °C

Main Results and Discussion

Chlorophyll Removal

• UV-Vis measurements at 664, 647 and 630 nm showed over 95 % reduction in green pigment for both matrices

Analyte Recovery and Precision

• Average recoveries ranged from 70 to 120 % for all 12 planar pesticides
• Reproducibility was excellent (%RSD < 5 %), except chlorothalonil at 20 % RSD
• Chromatograms exhibited clear, well-resolved peaks with minimal matrix interference

The sorbent combination of graphitized carbon, Z-Sep+ and primary-secondary amine provided an optimal balance between pigment removal and analyte retention, outperforming traditional carbon sorbents in the recovery of planar pesticides.

Benefits and Practical Applications

Ultrapure extracts enable accurate quantitation of trace planar pesticides in leafy foods, supporting quality control and regulatory testing laboratories. The streamlined QuEChERS workflow with SupelTM QuE Verde reduces sample preparation time and solvent use while maintaining robust recoveries, making it suitable for routine pesticide monitoring in agricultural and food safety settings.

Future Trends and Opportunities

Further developments may include:

• Extension of the cleanup strategy to other high-pigment botanical matrices
• Integration with high-resolution MS or tandem MS for multi-residue screening
• Automation of QuEChERS workflows to increase throughput
• Design of novel sorbent blends tailored to emerging pesticide chemistries

Conclusion

SupelTM QuE Verde QuEChERS cleanup delivers exceptional chlorophyll removal and maintains high recoveries of planar pesticides in spinach and fresh oregano. The method meets AOAC performance criteria and offers an efficient, reliable approach for pesticide residue analysis in challenging herbal and leafy matrices.

References

1. AOAC Official Method 2007.01. Pesticide Residues in Foods by Acetonitrile Extraction and Partitioning with Magnesium Sulfate.