Hydrogen Carrier Gas for Analyzing Pesticides in Pigmented Foods with GC/MS/MS

Significance of the Topic

The shortage and rising cost of helium have driven the search for alternative carrier gases in gas chromatography–mass spectrometry (GC/MS). Hydrogen offers faster separations, improved chromatographic efficiency, and sustainable operation, but its chemical reactivity poses challenges to sensitivity and spectral integrity. Developing robust strategies for routine pesticide analysis with hydrogen carrier gas is essential to ensure regulatory compliance and maintain analytical performance in complex food matrices.

Objectives and Study Overview

This work evaluated the use of hydrogen as the carrier gas for triple quadrupole GC/MS/MS (GC/TQ) analysis of over 200 pesticides in pigmented spinach using Agilent 8890/7000E and 8890/7010C systems. Key goals were to match retention times established with helium, preserve spectral fidelity for identification and quantitation, achieve detection limits at or below regulatory maximum residue limits (10 ppb), and demonstrate method robustness in challenging matrices.

Methodology and Instrumental Setup

Sample Preparation and Cleanup

• QuEChERS extraction of spinach followed by Agilent Captiva EMR–HCF1 pass-through cleanup to remove pigments and lipids.
• Addition of analyte protectants (ethylglycerol, D-sorbitol, L-gulonolactone) via sandwich injection to stabilize labile pesticides.

Injection Conditions

• Agilent multimode inlet in solvent-vent mode, 2 µL injection, 2 mm dimpled liner, starting at 60 °C ramping to 280 °C.
• High vent flow (100 mL/min) to eliminate solvent and protect early-eluting compounds.

Column Configuration and GC Parameters

• Minibore midcolumn backflush setup using two Agilent HP-5ms UI columns (20 m × 0.18 mm × 0.18 µm) for a 20 min method translated from helium to hydrogen.
• Retention time locking to chlorpyrifos-methyl ensured precise alignment with helium reference methods.

Electron Ionization Source Options

• Standard Inert Plus Extractor (XTR), HydroInert, and High Efficiency Source (HES) were compared.
• HydroInert and HES minimized in-source reactions, preserving spectral fidelity for reactive pesticides.

Data Acquisition

• Dynamic multiple reaction monitoring (dMRM) for sensitive quantitation of 203 pesticides with up to 52 concurrent transitions.
• Simultaneous dMRM/scan mode enabled full-scan spectral deconvolution and retrospective library searches without compromising quantitation.

Main Results and Discussion

Chromatographic Performance

• Hydrogen carrier gas achieved equivalent or better resolution than helium with identical oven programs.
• Minibore columns and retention time locking simplified method translation, preserving elution order and retention times.

Injection and Protectant Effects

• Solvent-vent injection and analyte protectants increased average response ~10-fold compared to unoptimized injections.
• High inlet temperature ramping ensured complete transfer of analytes while minimizing thermal degradation.

Source Comparison

• Standard EI source with hydrogen showed severe sensitivity loss and distorted spectra for nitro- and halogenated pesticides (e.g., tecnazene, alpha-BHC).
• HydroInert and HES sources restored spectral match scores (>90) and enabled use of existing MRM transitions and collision energies.
• HES on the 7010C system provided higher sensitivity and lower method detection limits (often <0.5 ppb) than HydroInert on the 7000E.

Calibration and Detection Limits

• Linear or quadratic calibration met SANTE 11312/2021 criteria, with relative standard error <20% for >94% of compounds.
• Over 92% of pesticides were quantitated at or below 10 ppb (default MRL) in spinach.
• Matrix-matched method detection limits (MDLs) were sub-ppb for most analytes, even those prone to hydrogenation.

Matrix Effects and Ruggedness

• Full-scan monitoring of total ion chromatograms guided inlet loading to prevent source overloading by spinach or pepper extracts.
• High throughput 10 min methods with hydrogen were feasible for smaller panels of ~100 pesticides, maintaining resolution comparable to helium.
• Long-term repeatability (>700 injections) was achieved with minimal maintenance using optimized injection and protectant protocols.

Screening and Identification

• dMRM/scan mode allowed simultaneous targeted quantitation and library-based identification of pesticides like tecnazene with high match scores under hydrogen.
• Preserved spectra facilitated rapid compound confirmation and retrospective data mining without reanalysis.

Benefits and Practical Applications of the Method

• Eliminates dependence on helium, reducing cost and supply risks.
• Improves chromatographic speed or resolution without method redevelopment.
• Maintains sensitivity and specificity required for regulatory pesticide residue testing in complex food matrices.
• Enables seamless adoption of existing helium-based MRM libraries and retention time methods.
• Supports high throughput screening with simultaneous quantitation and compound identification.

Future Trends and Potential Applications

• Expansion to other challenging matrices (environmental, pharmaceutical, forensic) using hydrogen carrier gas with inert sources.
• Further miniaturization and faster GC workflows (e.g., 5–10 min methods) leveraging high-efficiency columns.
• Integration with advanced data processing tools for fully automated screening and retrospective analysis.
• Adoption of hydrogen carrier gas in routine quality control and high-throughput laboratories seeking sustainable practices.

Conclusion

The optimized GC/TQ method using hydrogen carrier gas, solvent-vent injection, analyte protectants, and inert EI sources (HydroInert or HES) provides a practical alternative to helium for pesticide residue analysis. It delivers matched retention times, restored spectral fidelity, sub-ppb detection limits, and robust quantitation across a broad panel of 203 pesticides in pigmented spinach, meeting regulatory guidelines with minimal method translation effort.

Instrumental Setup

• GC: Agilent 8890 with multimode inlet (solvent vent), midcolumn backflush, minibore HP-5ms UI columns (20 m × 0.18 mm × 0.18 µm) at 1.0–1.2 mL/min H₂.
• MS: Agilent 7000E with HydroInert source and 7010C with HES; dMRM and dMRM/scan acquisition; source 280 °C; quads 150 °C; collision gas N₂, 1.5 mL/min.
• Sample Prep: QuEChERS extraction, Captiva EMR–HCF1 cleanup, analyte protectants in sandwich injection.

References

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