UPLC-MS/MS Determination of Paraquat and Diquat in Potato and W heat Using the CORT ECS UPLC HILIC Column

Importance of the Topic

Monitoring residues of paraquat and diquat in food commodities is essential due to their widespread use as quaternary ammonium herbicides and the strict regulatory limits set by agencies such as the US EPA and the EU. Their high polarity makes them challenging targets for reversed-phase chromatography, often necessitating complex sample preparation or ion-pair reagents that can compromise mass spectrometric sensitivity.

Objectives and Study Overview

The main goal was to develop a rapid, robust, and sensitive UPLC-MS/MS method for the simultaneous determination of paraquat and diquat in potato and wheat matrices. Key aims included improving chromatographic retention and resolution without ion-pairing reagents, achieving limits of quantitation below regulatory thresholds, and simplifying sample preparation for high-throughput screening.

Methodology and Instrumentation

The separation employed a CORTECS UPLC HILIC column (1.6 µm, 2.1 × 100 mm) with an isocratic mobile phase (50:50 acetonitrile/200 mM ammonium formate pH 3.7) at 0.5 mL/min and 30 °C. Detection was by positive electrospray ionization on an ACQUITY TQD MS/MS. Multiple reaction monitoring transitions included m/z 183.1→157.1 and 183.1→130.1 for diquat, and 185.1→170.1 and 171.1→77.0 for paraquat. Sample preparation used simple extraction: 10 g potato or 4 g wheat flour spiked with standards, extracted with 50:50 methanol/0.1 M HCl or water, heated, centrifuged, filtered, and diluted 1:1 with acetonitrile.

Main Results and Discussion

Baseline separation of both analytes was achieved in under four minutes. Extracted-ion chromatograms at 10 ppb fortification levels in wheat flour showed sharp, well-resolved peaks with no coelution. The isocratic HILIC method eliminated the need for ion-pairing agents, preventing ion suppression and boosting MS sensitivity. Limits of quantitation were below 10 ng/g for both compounds in potatoes and wheat flour, meeting or exceeding EU and US EPA requirements.

Benefits and Practical Applications

• Fast analysis cycle (<4 min) enables high sample throughput.
• Simple, minimal sample preparation reduces labor and plasticware use.
• No ion-pair reagents preserve MS performance and instrument cleanliness.
• Achieves regulatory LOQs for routine screening in food safety labs.

Instrumentation Used

• UPLC: ACQUITY UPLC H-Class System
• Column: CORTECS UPLC HILIC 1.6 µm, 2.1 × 100 mm
• Mass Spectrometer: ACQUITY TQD

Future Trends and Opportunities

Future developments may extend this HILIC approach to other highly polar pesticides and metabolites. Integration with high-resolution mass spectrometry could further enhance selectivity and confirmatory power. Automation of sample workup, miniaturized extraction formats, and multiplexed UPLC systems will support even higher throughput and lower environmental footprint.

Conclusions

The CORTECS UPLC HILIC method combined with MS/MS detection offers a rapid, sensitive, and straightforward solution for quantifying paraquat and diquat in potato and wheat. Its isocratic run and simple extract-and-dilute workflow meet stringent regulatory LOQs while maximizing laboratory efficiency.

References

1. Kohlberg D.I.S.; Mack D.; Anastassiades M.; Hetmanski M.T.; Fussell R.J.; Meijer T.; Mol H.G.J. Anal. Bioanal. Chem. 404, 2465–2474 (2012).
2. Anastassiades M.; Kolberg D.I.; Mack D.; Wildgrube C.; Sigalova I.; Roux D.; Fügel D. Quick Method for the Analysis of Residues of numerous Highly Polar Pesticides in Foods of Plant Origin involving Simultaneous Extraction with Methanol and LC-MS/MS Determination. EU Reference Laboratory for Pesticides requiring Single Residue Methods, Version 7 (Dec 2012).