Quantitative Analysis of Highly Polar Pesticides in Food Using SFC/MS

Significance of the Topic

Highly polar pesticides often escape reliable quantification using standard LC/MS workflows because their low retention and strong interaction with reversed-phase or HILIC columns impede simultaneous analysis. Developing a unified, high-throughput method for these compounds is critical for food safety monitoring, regulatory compliance, and efficient quality control in agricultural produce.

Objectives and Study Overview

This study demonstrates a batch analysis approach for multiple highly polar pesticides using supercritical fluid chromatography coupled to tandem mass spectrometry (SFC/MS/MS). Key aims include:

• Designing a single chromatographic run to cover a wide polarity range of pesticides (logP −3.47 to 1.96).
• Optimizing mobile phase composition—particularly water content in organic modifier—to achieve sufficient retention and elution.
• Evaluating quantitative performance via matrix-matched calibration in food extracts.

Methodology and Instrumentation

The analysis employed a Shimadzu Nexera UC SFC system coupled to an LCMS-8060 triple-quadrupole. Supercritical CO₂ (pump A) and acetonitrile with 0.5% formic acid plus 10 mM ammonium formate (pump B) served as the primary gradient. A separate low-pressure pump (pump C) delivered aqueous solution (water with 0.5% formic acid and 10 mM ammonium formate) after the modifier reached 100% to elute strongly retained analytes. Key parameters:

• Analytical column: Restek Ultra Silica, 150 × 2.1 mm, 3 μm
• Columnoven temperature: 50 °C; flow rate: 0.8 mL/min (0.6 mL/min during mid-gradient)
• Make-up solvent: methanol, 0.2 mL/min (pump D)
• MS conditions: Heated ESI, interface 300 °C, desolvation line 250 °C, heating block 350 °C, scan speed 15,000 u/sec, MRM dwell 3 ms
• Sample preparation: QuPPe extraction of flaxseed and lemon matrices followed by direct injection

Main Results and Discussion

• Modifier Optimization: Adding incremental water (0.2–10%) to acetonitrile revealed that 6% water provided optimal peak shapes and retention for most analytes. Beyond this, gradient accuracy suffered in the presence of supercritical CO₂.
• Separate Aqueous Delivery: Introduction of pump C after modifier plateau allowed elution of nicotine and kasugamycin, which remained strongly retained under standard conditions.
• Chromatographic Coverage: Successful batch separation of twelve pesticides spanning logP −3.47 (chlormequat) to 1.96 (kasugamycin) within a 20-minute gradient.
• Quantitative Performance: Matrix-matched calibration (10–200 ppb) in lemon and flaxseed extracts yielded excellent linearity (R² > 0.996) and repeatability (RSD 1.75–10.74% at 100 ppb) for eight representative analytes.

Benefits and Practical Applications of the Method

• Comprehensive Analysis: Single-run quantitation of multiple highly polar pesticides simplifies workflows and reduces analysis time.
• Enhanced Retention Control: Fine-tuning water in the modifier plus post-gradient aqueous addition extends the range of elutable compounds.
• Regulatory Compliance: Robust matrix calibration supports accurate monitoring in diverse food samples.
• High Throughput: Integration with automated sample introduction and low-pressure gradient blending streamlines routine testing in QA/QC labs.

Future Trends and Potential Applications

• Method Extension: Applying the SFC/MS approach to other challenging polar analytes such as metabolites, pharmaceuticals, and food contaminants.
• Column Development: Tailoring novel silica-based stationary phases to further enhance selectivity for structurally diverse polar compounds.
• Automation Advances: Integrating in-line sample cleanup or QuPPe extraction modules for fully automated polar pesticide workflows.
• Regulatory Harmonization: Standardizing SFC/MS methods across laboratories to support global pesticide monitoring programs.

Conclusion

The described SFC/MS/MS method offers a unified solution for quantifying highly polar pesticides in food matrices, overcoming limitations of conventional LC/MS by leveraging supercritical CO₂, optimized modifier composition, and targeted aqueous addition. The approach delivers robust retention, high throughput, and reliable quantitation, paving the way for broader adoption in food safety and environmental analysis.

Reference

1. Anastassiades M., et al. “QuPPe of EURL-SRM,” Version 9.1, 2016.
2. Fujito Y., Baker D., Barnes A., Titman C., Horner J., Loftus N. “Quantitative Analysis of Highly Polar Pesticides in Food Using SFC/MS,” Shimadzu Application News No. C162, Nov. 2017.