Use of Nitrogen as an Alternative Carrier Gas to Helium for GC- MS/MS with APGC Technology for the Determination of Pesticide Residues in Food

Importance of the Topic

Gas chromatography–mass spectrometry (GC-MS) is a cornerstone of pesticide residue analysis in food safety laboratories. Helium, traditionally used as the carrier gas, faces increasing supply constraints and cost pressures. Switching to nitrogen as a carrier gas promises significant cost savings and uninterrupted availability. Atmospheric Pressure Gas Chromatography (APGC) technology inherently uses nitrogen in its ionization source, offering a pathway to maintain sensitivity and chromatographic performance when replacing helium.

Objectives and Overview

This study aimed to demonstrate a straightforward conversion of an established GC-MS/MS method for 203 pesticide residues from helium to nitrogen carrier gas using APGC technology. Key goals included preserving retention times, resolution, sensitivity, and run times while leveraging standard nitrogen supplies.

Methodology

• A Restek Rxi-5Sil MS column of 30 m × 0.25 mm × 0.25 µm (helium method) was translated to a 20 m × 0.15 mm × 0.15 µm column for nitrogen using Restek’s EZGC method translator tool.
• Carrier gas linear velocity and holdup time were matched by adjusting column dimensions and flow rates.
• Initial oven temperature was lowered to improve solvent focusing when using acetonitrile injection solvent.
• Matrix-matched standards were prepared from QuEChERS extracts of cucumber and cottage-pie-style baby food, spiked with 203 pesticides at regulatory levels.

Instrumentation Used

• Waters Xevo TQ-S Micro triple quadrupole mass spectrometer equipped with an APGC source.
• Restek Rxi-5Sil MS GC columns (helium and nitrogen configurations).
• High-purity nitrogen with moisture filtration; controlled water introduction into the ionization chamber.
• Restek EZGC software for method translation.

Main Results and Discussion

• Retention times and run durations were nearly identical between helium and nitrogen methods after column scaling.
• Chromatograms for early and late eluters showed comparable peak shapes; a critical pesticide pair displayed improved resolution under nitrogen (APGC) conditions.
• Nearly 98% of the 203 pesticides were reliably detected at 0.005 mg/kg in both cucumber and baby-food matrices.
• Calibration curves met SANTE guidelines, with most residuals within ±20% tolerance.

Benefits and Practical Applications

• Rapid carrier-gas switching via a valve allows users to return to helium if needed.
• No loss of sensitivity or chromatographic performance despite the lower ionization energy of nitrogen.
• Substantial cost savings and elimination of helium supply shortages enhance lab productivity and budgeting.
• Applicable to routine pesticide monitoring workflows in food safety and quality-control laboratories.

Future Trends and Opportunities

• Broader adoption of nitrogen carrier gas across GC-MS platforms as helium scarcity persists.
• Further optimization of column chemistries and source conditions for diverse analyte classes.
• Integration of automated method translation tools and carrier-gas switching hardware.
• Expansion of APGC applications to other polar and thermally labile compounds.
• Contribution to sustainable laboratory operations by reducing reliance on finite gas resources.

Conclusion

The conversion from helium to nitrogen carrier gas in GC-MS/MS using APGC technology is straightforward and preserves analytical performance for pesticide residue determination. By scaling column dimensions and optimizing source parameters, laboratories can achieve equivalent sensitivity, resolution, and run times while benefiting from the cost-effectiveness and reliability of nitrogen.

Reference

• Gould D, Adams S, Hird S, Stevens D, Dorman F. Use of Nitrogen as an Alternative Carrier Gas to Helium for GC-MS/MS with APGC Technology for the Determination of Pesticide Residues in Food. Waters Corporation; 2023.