Determining Pesticides in Dietary Supplements with QuEChERS Extraction, Cartridge SPE, and GCxGC-TOFMS

Significance of the Topic

Regulatory guidelines for dietary supplements increasingly mirror those for pharmaceuticals, mandating rigorous pesticide residue testing. Botanical matrices present complex interferences that can compromise data integrity, making effective sample preparation and high-resolution analysis essential to ensure consumer safety and regulatory compliance.

Objectives and Study Overview

This study aimed to develop and validate a multiresidue pesticide method tailored to powdered and finished botanical supplements. By combining QuEChERS extraction, cartridge solid-phase extraction cleanup, and comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GCxGC-TOFMS), the approach was benchmarked against one-dimensional GC-TOFMS in terms of recovery, matrix interference removal, and quantification accuracy.

Methodology and Sample Preparation

Dietary supplement powders (dandelion root, sage, finished herbal blends) were wetted with water, fortified with internal standards and pesticide mixtures, and extracted using the EN 15662 QuEChERS protocol. Cleanup methods compared included:

• Dispersive SPE (dSPE) with PSA, C18, and graphitized carbon black sorbents
• Cartridge SPE (cSPE) using 6 mL Combo cartridges packed with CarboPrep® 90 and PSA

Following cleanup, extracts were concentrated under nitrogen, exchanged into toluene, and brought to 0.5 mL for analysis.

Instrumentation

Analyses were performed on a LECO Pegasus 4D GCxGC-TOFMS system and in single-dimension GC-TOFMS mode. Key components included:

• Primary column: 30 m × 0.25 mm × 0.25 µm Rxi-5Sil MS
• Secondary column: 1.5 m × 0.18 mm × 0.20 µm Rtx-200
• Helium carrier gas at 1.5–1.8 mL/min flow
• Electron ionization (70 eV), mass range 45–550 amu
• Thermal modulator cycle: 4 s separation time, 1.2 s hot pulse

Main Results and Discussion

dSPE cleanup proved inadequate for highly pigmented or complex supplements, yielding residual matrix bias. Cartridge SPE offered improved removal of interferences but one-dimensional GC-TOFMS still exhibited quantification bias in sage and finished product extracts. GCxGC-TOFMS significantly enhanced separation, spreading coeluting peaks into a two-dimensional retention plane. This led to:

• Accurate recoveries (70–110 %) across 46 pesticides in all matrices
• Unbiased quantification of Fenhexamid, Oxadixyl, Iprodione, and Cypermethrin, previously masked in 1D analysis
• Resolution of isobaric interferences for gamma-HCH (lindane), correcting overestimated recoveries

Benefits and Practical Applications

This workflow offers:

• Rapid, solvent-efficient extraction adaptable to dry botanical powders
• Enhanced matrix cleanup with cartridge SPE for complex supplements
• Superior chromatographic resolution via GCxGC-TOFMS, improving both qualitative and quantitative accuracy
• Applicability in QA/QC laboratories for regulatory compliance and batch release testing

Future Trends and Possibilities of Use

Advances may include:

• Automation of QuEChERS-SPE workflows for higher throughput
• Integration with high-resolution mass spectrometry for unknown screening
• Extension to other contaminant classes (e.g., mycotoxins, veterinary drugs)
• Enhanced data processing algorithms for rapid deconvolution in complex matrices

Conclusion

The combination of QuEChERS extraction, cartridge SPE cleanup, and GCxGC-TOFMS with orthogonal Rxi-5Sil MS and Rtx-200 columns provides a robust, accurate, and efficient platform for multiresidue pesticide analysis in botanical dietary supplements, overcoming limitations of traditional 1D GC methods.

References

1. Restek Corporation. Developing New Methods for Pesticides in Dietary Supplements: Advantages of the QuEChERS Approach. Application Note PHAN1242 (2010).
2. European Committee for Standardization. EN 15662: Foods of Plant Origin—Determination of Pesticide Residues Using GC-MS and/or LC-MS/MS Following Acetonitrile Extraction/Partitioning and Clean-up by Dispersive SPE (QuEChERS-method), Version 2008.
3. Wong JW, Wirtz MS, Hennessy MK, Schenck FJ, Krynitsky AJ, Capar SG. Pesticide residue analysis in dietary supplements. Acta Horticulturae 720 (2006) 113–120.