Paraquat and Diquat Analysis in Tea - An Agilent Bond Elut CBA SPE and LC/MS/MS method

Importance of the Topic

Monitoring paraquat and diquat residues in tea is critical due to their widespread use as herbicides and potential health risks. Regulatory agencies worldwide enforce strict limits on these polar pesticides, driving the need for reliable, sensitive, and efficient analytical methods. The combination of solid-phase extraction (SPE) and LC/MS/MS offers targeted cleanup and high selectivity for trace-level analysis in complex matrices such as tea.

Objectives and Study Overview

This Application Note presents a streamlined workflow for the determination of paraquat and diquat in tea. Key goals include development of an SPE cleanup procedure using Agilent Bond Elut CBA cartridges, optimization of extraction conditions, and implementation of a robust LC/MS/MS method with a Poroshell 120 HILIC-Z column to achieve high recovery, precision, and low detection limits.

Applied Methodology and Instrumentation

Sample pretreatment involves spiking 1 g of homogenized tea powder, slurrying with water and acidified methanol, heat-assisted extraction, centrifugation, dilution, pH adjustment with ammonium hydroxide, and EDTA addition to mitigate metal ion interference. The SPE cleanup uses Agilent Bond Elut CBA LRC cartridges conditioned with methanol and water, followed by sample loading, phosphate buffer and methanol washes, and elution with methanol/water/formic acid. LC/MS/MS analysis employs an Agilent InfinityLab Poroshell 120 HILIC-Z column (2.1×100 mm, 2.7 µm) at 35 °C, mobile phases of ammonium formate in water (pH 3) and formic acid in acetonitrile, 0.5 mL/min flow, 2 µL injection, and a triple quadrupole mass spectrometer operating in positive ESI mode.

Main Results and Discussion

The extraction solvent composed of 1:1 methanol/water with 5% formic acid provided the highest normalized recovery for both analytes. Incorporation of 20 mM EDTA enhanced absolute recovery above 80% with RSDs below 10%. Calibration over 2–400 ng/g (diquat) and 10–400 ng/g (paraquat) showed excellent linearity (R2 > 0.99). Quantitation at 20 ng/g and 200 ng/g yielded recoveries of 88–111% and RSDs under 9%. Chromatograms exhibited sharp, symmetrical peaks with retention times around 4.9 min (paraquat) and 5.2 min (diquat).

Benefits and Practical Applications

The presented approach delivers a rapid, high-throughput solution for routine monitoring of paraquat and diquat in tea. The use of CBA SPE cartridges simplifies sample cleanup, reduces matrix effects, and minimizes labor. Achieved sensitivity and precision meet regulatory requirements for quality control in food safety laboratories and agricultural monitoring programs.

Future Trends and Potential Applications

Anticipated developments include automated SPE systems to further increase throughput, integration with high-resolution mass spectrometry for broader pesticide screening, and expansion of the method to other polar contaminants in various food matrices. Advances in column technology may offer reduced analysis times and enhanced peak capacity for multi-residue applications.

Conclusion

This work demonstrates a robust and efficient LC/MS/MS-based method combining Agilent Bond Elut CBA SPE and a Poroshell HILIC-Z column for reliable quantitation of paraquat and diquat in tea. High recoveries, low RSDs, and strong linearity confirm the method’s suitability for compliance testing and routine food safety analysis.

Reference

• Chinese National Standard GB 2763.1-2018
• European Commission Regulation (EU), EU Pesticides database