Enhancing MRM Experiments in GC/MS/MS Using APGC

Significance of the Topic

Accurate detection of pesticide residues in food is crucial for consumer safety and regulatory compliance. While gas chromatography–mass spectrometry (GC–MS/MS) under electron ionization (EI) is widely used, extensive fragmentation can limit sensitivity and specificity.

Objectives and Overview of the Study

This work evaluates atmospheric pressure gas chromatography (APGC) coupled to a Waters Xevo TQ-S tandem quadrupole mass spectrometer for multi-residue analysis of 25 pesticides in fruits and vegetables. The aim is to compare APGC performance with conventional EI methods in terms of sensitivity, selectivity, and potential interferences.

Methodology and Instrumentation

Samples of apple, orange, tomato, and carrot were fortified and extracted using the QuEChERS approach. GC separations employed an Agilent 7890A system with a DB-5MS column under a temperature program from 70 °C to 300 °C. The Xevo TQ-S instrument with APGC source operated at 1.8 µA corona pin current, nitrogen cone gas and make-up gas flows, and TargetLynx software for MRM data acquisition.

Instrumental Setup

• GC: Agilent 7890A, DB-5MS (30 m × 0.25 mm, 0.25 µm)
• Injector: Splitless mode, 280 °C
• Carrier gas: Helium at 2 mL/min
• MS: Waters Xevo TQ-S with APGC source
• Ionization: Atmospheric pressure GC, corona pin 1.8 µA
• Software: MassLynx v4.1 with TargetLynx

Main Results and Discussion

APGC produced abundant [M+H]+ ions with minimal fragmentation, enhancing precursor selection for MRM transitions. A spectral comparison for chlorpyrifos demonstrated that APGC preserves the molecular ion as the base peak, whereas EI generates extensive fragment peaks. Selectivity tests revealed that APGC transitions prevented false positives—for example, heptachlor epoxide B interference encountered under EI was eliminated using a unique APGC MRM. Linearity studies in solvent over 0.1–100 ppb showed r2 > 0.99 for most analytes. Limits of quantification in fortified extracts ranged from 0.02 to 2 ppb, with negligible matrix effects across different fruits and vegetables.

Benefits and Practical Applications

• Enhanced sensitivity and lower detection limits for GC-amenable pesticides
• Improved selectivity with intact molecular ions, reducing false positives
• Single-platform analysis of both GC and LC compounds on the same MS
• Reduced matrix interferences, enabling sample dilution and lower maintenance
• Compliance with stringent regulatory requirements for food safety testing

Future Trends and Opportunities

Integration of APGC with high-resolution mass spectrometry may further improve structural elucidation. Development of expanded MRM libraries and automated workflows can streamline routine pesticide monitoring. Miniaturized APGC sources and alternative ionization schemes could extend the approach to broader chemical classes.

Conclusion

The APGC–Xevo TQ-S combination provides a robust, high-sensitivity solution for multi-residue pesticide analysis by generating abundant molecular ions and enhancing MRM selectivity. This unified platform offers significant advantages over traditional EI-GC–MS/MS, making it ideal for routine food testing laboratories.

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