Determination of polar pesticides in grapes using a compact ion chromatography system coupled with tandem mass spectrometry

Significance of the Topic

The analysis of polar ionic pesticides such as glyphosate and its metabolites in fruits is crucial for food safety, regulatory compliance, and public health assurance. These compounds are widely used yet challenging to detect due to their high polarity, low retention in conventional chromatography, and matrix interferences. A streamlined, sensitive multiresidue method helps laboratories meet stringent maximum residue levels (MRLs) and supports routine monitoring.

Objectives and Overview

This work aimed to develop, validate, and demonstrate a workflow for determining 16 polar pesticides and related metabolites in grapes using a compact ion chromatography (IC) system coupled to a triple quadrupole tandem mass spectrometer (MS/MS). Goals included compliance with EU and U.S. regulatory criteria for MRLs and method validation guidelines.

Methodology and Used Instrumentation

A simplified QuPPe-based extract, replacing acidified solvents with pure methanol and including an OnGuard II RP clean-up cartridge, was used to prepare grape samples. Ion chromatography separation employed a Thermo Scientific Dionex Integrion HPIC system fitted with IonPac AS19-4µm guard and analytical columns. Continuous KOH eluent generation and suppression used EGC 500 cartridges, CR-ATC trap, and ADRS 600 suppressor. A post-column make-up flow of acetonitrile enhanced electrospray ionization. Detection was performed on a Thermo Scientific TSQ Quantis triple quadrupole MS in negative selected reaction monitoring (SRM) mode. Chromeleon CDS and TraceFinder software managed data acquisition and processing.

Main Results and Discussion

Retention times for all 16 analytes were stable within ±0.1 min in grape matrix. Calibration was linear over 1–50 µg/L for neat standards, extending to 100 µg/L in matrix-matched and matrix-extracted standards, with r2 values above 0.995. Limits of quantification were well below EU MRLs (e.g., glyphosate LOQ 1 µg/kg vs. MRL 500 µg/kg). Recoveries at spiking levels of 20 and 100 µg/kg ranged from 70% to 120% with relative standard deviations below 10%. The method effectively separated coeluting species such as fosetyl and phosphonic acid, and qualifier/quantifier ion ratios met regulatory tolerances.

Benefits and Practical Applications

• Rapid 20 min run time for 16 analytes with minimal sample preparation.
• High sensitivity and selectivity through IC-MS/MS for compliance with low MRLs.
• Matrix-matched calibration compensates for residual interferences.
• Workflow integrates easily into routine food-testing laboratories.

Future Trends and Possibilities

• Extension to other high-water-content commodities such as berries and vegetables.
• Integration of high-resolution MS for broader screening of unknown polar compounds.
• Automated sample preparation platforms to increase throughput and reduce manual steps.
• Data-mining strategies to link pesticide residues with geographic and agronomic factors.

Conclusion

The presented IC-MS/MS workflow combining a simplified QuPPe extraction and compact IC system meets validation criteria for sensitivity, accuracy, and robustness. It enables efficient multiresidue analysis of polar pesticides in grapes, facilitating regulatory compliance and routine monitoring in food safety laboratories.

References

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