Achieving the MRLs with Hydrogen Carrier Gas: GC/MS/MS Analysis of 200 Pesticides in Produce

Importance of the Topic

Pesticide residue analysis in food products is critical for ensuring consumer safety and regulatory compliance. Rising helium shortages and price increases motivate the adoption of hydrogen as an alternative GC carrier gas. While hydrogen offers similar chromatographic performance, its reactivity may affect analyte stability, spectral fidelity, and sensitivity if not properly addressed.

Goals and Study Overview

This study evaluated the translation of a 20-minute GC/MS/MS method for 203 pesticides from helium to hydrogen carrier gas. Key objectives included maintaining retention time accuracy, chromatographic resolution, mass spectral integrity, and sensitivity sufficient to meet maximum residue limits (MRLs) in a spinach QuEChERS extract.

Methodology and Instrumentation

Sample Preparation and Cleanup:

• Spinach QuEChERS extract following standard extraction and matrix cleanup workflows.
• Midcolumn backflushing to reduce matrix buildup.

GC/MS/MS Conditions:

• Injection: Solvent-vent mode, 2 µL, 2 mm dimpled liner, initial 60 °C (0.1 min), ramp to 280 °C at 600 °C/min.
• Columns: Two 20 m × 0.18 mm × 0.18 µm HP-5ms UI capillaries connected via Purged Ultimate Union.
• Oven program: 60 °C (1 min) → 170 °C at 40 °C/min → no hold → 310 °C at 10 °C/min (2.25 min hold).
• Carrier gas flows: 1.1 mL/min and 1.3 mL/min hydrogen.

Mass Spectrometer and Ion Source Hardware:

• Conventional EI source.
• Hydrogen-optimized HydroInert EI source.
• High-Efficiency Source (HES) EI configuration.

Main Results and Discussion

Retention Time and Resolution:

• Retention time locking enabled transfer of 20-minute pesticide separations from helium to hydrogen with identical elution order.
• A 10-minute hydrogen method achieved comparable chromatographic resolution to the helium-based 20-minute run.

Mass Spectral Fidelity:

• Conventional EI with hydrogen caused spectral distortion for reactive pesticides (e.g., tecnazene), altering ion ratios and library matching scores.
• HydroInert and HES sources preserved ion ratios and matched reference spectra, allowing reuse of existing spectral libraries and MRM transitions.

Sensitivity and Quantitation:

• Non-reactive pesticides showed a 2–5× increase in detection limits with hydrogen compared to helium.
• Reactive compounds suffered >100× sensitivity loss with a conventional source but recovered full sensitivity with HydroInert and HES sources.
• Tecnazene quantitation down to 0.5 ppb was achieved using optimized sources, meeting the default 10 ppb MRL.

Calibration Performance:

• Over 90 % of the 203 pesticides were quantified at or below 0.01 mg/kg (10 ppb).
• More than 90 % met criteria for limit of quantitation, precision (RSD ≤ 20 %), and linearity (R² ≥ 0.99).

Benefits and Practical Applications

• Hydrogen serves as a cost-effective, readily available GC carrier offering equal or improved separation performance.
• Optimized ion source hardware enables seamless adoption without redeveloping spectral libraries or MRM methods.
• Shorter runtimes (10 minutes) are feasible without sacrificing resolution or sensitivity, enhancing laboratory throughput.

Future Trends and Potential Applications

• Broader implementation of hydrogen carrier gas workflows in routine food-safety and environmental laboratories.
• Further refinement of ion source designs to minimize in-source reactions and improve robustness.
• Expansion of hydrogen-based methods to other matrices (fruits, vegetables, cereals) and analyte classes.
• Integration with high-throughput automation platforms and advanced data processing for rapid screening.

Conclusion

This work demonstrates that with proper method conversion, retention time locking, and hydrogen-optimized EI sources, hydrogen carrier gas can reliably replace helium for GC/MS/MS pesticide analysis. Analytical performance—including retention time precision, chromatographic resolution, mass spectral fidelity, and sensitivity—meets or exceeds regulatory requirements for MRL compliance.

Reference

1 EI GC/MS Instrument Helium to Hydrogen Carrier Gas Conversion. User Guide. Agilent Technologies. 5994-2312EN. 2022.
2 Five Keys to Unlock Maximum Performance in the Analysis of Over 200 Pesticides in Challenging Food Matrices by GC/MS/MS. Agilent Technologies. 5994-4965EN. 2022.