Routine UPLC-MS/MS Quantification of Pesticide Residues in Okra with Simultaneous Acquisition of Qualitative Full-Spectrum MS and MS/MS Data

Importance of the Topic

Okra is a staple vegetable in tropical regions and is prone to pest infestations, leading to the widespread application of pesticides. Monitoring pesticide residues at or below legislative maximum residue limits (MRLs) is essential to ensure food safety, protect consumer health, and comply with international trade regulations.

Objectives and Overview of the Study

This study develops and validates a high‐throughput UPLC‐MS/MS method for the simultaneous quantitative and qualitative analysis of 212 pesticide residues in okra. Key aims include

• Achieving sensitive detection at legislative limits in a single injection.
• Assessing matrix effects and employing advanced data acquisition for confident compound confirmation.

Methodology and Used Instrumentation

Okra samples were prepared using the QuEChERS AOAC 2007.01 protocol: homogenization, acidified acetonitrile extraction, and dispersive SPE cleanup. Chromatographic separation was performed on an ACQUITY UPLC H-Class System with an HSS T3 column (2.1×100 mm, 1.8 µm) at 45 °C, using a gradient of 10 mM ammonium acetate in water and methanol at 0.45 mL/min. Tandem MS analysis employed a Xevo TQD with rapid ESI+/- polarity switching, acquiring two MRM transitions per analyte alongside product ion confirmation scans. RADAR technology captured full‐scan background spectra concurrently.

Main Results and Discussion

All 212 pesticides were detected at 10 ppb (0.01 mg/kg), consistent with common MRLs. Calibration in solvent and matrix‐matched standards (1–50 ppb) demonstrated strong linearity (R² > 0.99 for most compounds). Recovery studies at 10 ppb yielded 25–150% recoveries with RSDs below 20% for the majority. Significant matrix effects (>50% suppression or enhancement) were observed for most analytes, underscoring the need for matrix‐matched calibration. RADAR data revealed co‐eluting interferences—for example, a m/z 217.1 ion causing 48% suppression of dimethoate—while aldicarb exhibited minimal interference (0.4%). PICS scans provided on‐the‐fly MS/MS spectra for peak confirmation, enhancing identification confidence.

Benefits and Practical Applications of the Method

This integrated UPLC-MS/MS approach offers:

• Simultaneous detection and quantification of a broad pesticide panel in a single run.
• Improved specificity via dual MRM transitions and product ion confirmation.
• Insight into matrix background and ionization effects using RADAR full‐scan data.
• Robust quantification through matrix‐matched calibration strategies.

Future Trends and Opportunities

Emerging high‐resolution mass spectrometry (HRMS) platforms could enable non-target screening alongside targeted analysis.
Automation of sample preparation and data processing will further increase throughput and reproducibility.
Extension of this workflow to other challenging matrices (e.g., high-fat or high-sugar foods) may require optimized cleanup and internal standard protocols.

Conclusion

The described UPLC-MS/MS method reliably quantifies multi-residue pesticides in okra at legislative thresholds, combining QuEChERS extraction, matrix-matched calibration, RADAR full scan, and PICS for comprehensive qualitative and quantitative assurance in complex food matrices.

Reference

1. FAO. FAOSTAT. http://faostat.fao.org/.
2. National Horticulture Board. Okra Production Data. http://www.ncpahindia.com/okra.php.
3. APEDA. Procedure for Okra Export to EU. http://www.apeda.gov.in/apedawebsite/Announcements/procedureokraeu.pdf.
4. UK CRD. PRiF Q4 2012 Report. http://www.pesticides.gov.uk/Resources/CRD/PRiF/Documents/Results%20and%20Reports/2012/Q4%202012%20Final.pdf.
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6. SANCO/10684/2009. Method validation and quality control procedures for pesticide residues analysis in food and feed.
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