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

Importance of the Topic

Polar ionic pesticides such as glyphosate, AMPA, and fosetyl pose analytical challenges due to their high polarity, low extraction recoveries, and poor retention on reversed-phase columns. Reliable monitoring of these residues in grapes is critical for food safety, regulatory compliance, and public health.

Objectives and Study Overview

This work aimed to develop and validate a rapid ion chromatography–tandem mass spectrometry (IC-MS/MS) method for simultaneous determination of 16 polar pesticides and metabolites in grapes. The method was designed to meet European Union maximum residue levels (MRLs) and SANTE/11813/2017 validation criteria while simplifying sample preparation.

Methodology and Instrumentation

• Sample Preparation: Modified QuPPe extraction using non-acidified methanol followed by cleanup with OnGuard II RP cartridges to reduce matrix effects.
• Chromatography: Dionex Integrion HPIC system with IonPac AS19-4 µm guard (2 × 50 mm) and analytical (2 × 250 mm) columns; KOH eluent gradient from 15 to 75 mM over a 20 min run.
• Detection: Dionex ADRS 600 suppressor in AutoSuppression mode, suppressed conductivity monitoring, and post-column addition of acetonitrile (0.2 mL/min) to enhance electrospray sensitivity.
• Mass Spectrometry: Thermo Scientific TSQ Quantis triple quadrupole in negative electrospray SRM mode; optimized transitions for each analyte.
• Calibration: Matrix-matched and matrix-extracted standards prepared across ranges covering EU MRLs for table grapes.

Main Results and Discussion

• Chromatographic Performance: Baseline separation of all 16 analytes in a 20 min run, including resolution of fosetyl and phosphonic acid. Retention time stability was within ±0.1 min.
• Sensitivity and Linearity: Calibration curves demonstrated r2 > 0.995 over ranges 1–100 µg/L for most analytes. Limits of quantitation were below EU MRLs (0.01–100 mg/kg).
• Recovery and Precision: Recoveries ranged from 79 % to 103 % at spiking levels of 20 and 100 µg/kg (RSD 0.9–11 %).
• Selectivity: SRM qualifier/quantifier ion ratios were within ±30 % of expected values, confirming absence of coeluting interferences in grape matrix.

Benefits and Practical Applications

• Streamlined Workflow: Direct IC-MS/MS analysis eliminates need for derivatization and extensive cleanup.
• Regulatory Compliance: Method meets EU SANTE guidelines and MRL requirements for grapes.
• High Throughput: 20 min analysis time and automated sample handling support routine monitoring in QA/QC laboratories.

Future Trends and Potential Applications

• Matrix Expansion: Adaptation to other fruits, vegetables, and environmental samples.
• Automation: Integration of online cleanup and multiplex IC systems for higher sample throughput.
• Broader Panels: Inclusion of additional ionic contaminants and emerging polar agrochemicals.
• Portable IC-MS: Development of miniaturized, field-deployable systems for on-site testing.

Conclusion

The developed method combining a modified QuPPe extraction with IC-MS/MS offers a robust, sensitive, and efficient approach for multiresidue analysis of polar pesticides in grapes. It complies with regulatory standards, reduces sample preparation complexity, and delivers high throughput for routine food safety testing.

Used Instrumentation

• Dionex Integrion HPIC system (eluent generator, pump, degasser, suppressor, conductivity detector).
• Dionex IonPac AS19-4 µm guard and analytical columns.
• Dionex AS-AP autosampler and OnGuard II RP cartridges.
• Thermo Scientific TSQ Quantis triple quadrupole mass spectrometer.

References

• European Commission SANTE/11813/2017 guidelines on pesticide residue method validation.
• Thermo Fisher Scientific technical and product manuals for IC and MS instrumentation.
• Government Accountability Office report GAO-15-38 on glyphosate residue testing.