Multi-class pesticides analysis in challenging vegetable matrices using fast 5 msec MRM with 15 msec polarity switching

Significance of the Topic

Ensuring the safety of vegetables against pesticide residues is a global challenge due to varying regulatory limits and the need for broad multi-class screening in a single analytical run. Fast, sensitive methods are essential for routine monitoring in food safety laboratories to meet or exceed maximum residue limits (MRLs) set by regulatory bodies.

Objectives and Study Overview

This study evaluated the performance of an ultra-fast tandem mass spectrometry method for the analysis of 138 pesticides in vegetable matrices. Key aims were to:

• Apply a 5 millisecond multiple reaction monitoring (MRM) approach with 15 millisecond polarity switching.
• Assess limits of quantification (LOQs) for both LC-QqQ and GC-QqQ target lists from the EU Reference Laboratory (EURL) method.
• Evaluate recovery and matrix effects in challenging vegetable samples (paprika and leek).

Methodology and Instrumentation

Sample preparation followed the QuEChERS EU method:

• Homogenization of 10 g vegetable sample with 10 mL acetonitrile and salt mixture (MgSO4, NaCl, citrate salts).
• Vigorous hand shaking, centrifugation, dispersive SPE clean-up (PSA, MgSO4, ENVI-Carb), followed by filtration.

Analytical conditions:

• UHPLC: Nexera system with Shim-pack XR-ODSII column (75 × 2 mm, 2.2 µm).
• Mobile phase A: 2 mM ammonium formate/0.1% formic acid in water; B: methanol; gradient elution over 20 minutes.
• Triple quadrupole MS: LCMS-8040 with ESI in positive and negative modes, 276 MRM transitions (2 per compound), 5 ms dwell time, 1 ms pause, 15 ms polarity switch.
• Instrument features: 5× sensitivity gain, 15 000 u/sec scan speed, 555 ch/sec MRM speed.

Main Results and Discussion

Quantification limits:

• LC-QqQ method achieved LOQs below 10 ppb for all 72 evaluated pesticides.
• GC-QqQ method reached LOQs below 10 ppb for 47 of 66 targets (71%), with six between 10–50 ppb and 13 not ionized.

Linearity and calibration demonstrated excellent response up to 500 ppb for representative compounds. Recovery tests at 5 ppb spike level showed approximately 90% of pesticides with recoveries between 70–120% across paprika and leek. A few compounds exhibited elevated apparent recoveries due to matrix background, highlighting the importance of blank monitoring.

Benefits and Practical Applications

The fast MRM approach allows comprehensive multi-residue screening in a single 20 minute run, reducing analysis time and solvent consumption. High sensitivity and rapid polarity switching ensure reliable detection at or below regulatory MRLs. This method supports routine food safety testing, quality control in agricultural production, and compliance with international standards.

Future Trends and Possibilities

Potential advancements include:

• Expansion of target lists to emerging pesticides and degradation products.
• Integration with high-resolution mass spectrometry for non-target screening.
• Automation of sample preparation and data processing using AI algorithms.
• Miniaturized or portable MS systems for field testing.

Conclusion

Ultra-fast 5 ms MRM with 15 ms polarity switching on the LCMS-8040 platform successfully quantified a broad range of pesticides in complex vegetable matrices. The method meets stringent LOQ requirements and offers robust recoveries, streamlining multi-class pesticide analysis for regulatory and industrial laboratories.

Reference

Shimadzu application note PO-CON1216E (2012)