Quantitation of Paraquat Residue in Milk Using the Agilent 6470 Triple Quadrupole LC/MS

Importance of the Topic

Milk is a staple food consumed worldwide and can be contaminated by herbicide residues such as paraquat, a moderately toxic quaternary amine. Accurate monitoring of paraquat in dairy products is critical for consumer safety and regulatory compliance. Advanced mass spectrometry techniques offer the sensitivity and selectivity required to detect low-level residues in complex food matrices.

Study Objectives and Overview

This application study aims to establish a robust and sensitive LC/MS/MS method for quantifying paraquat in milk. The approach focuses on simplified sample preparation, efficient chromatographic separation using HILIC-Z chemistry, and selective detection via multiple reaction monitoring (MRM) on an Agilent 6470 triple quadrupole mass spectrometer.

Methodology and Instrumentation

Sample preparation:

• QuEChERS extraction followed by dispersive solid-phase cleanup using dSPE kits
• Dilution of extracts prior to analysis

Chromatography and detection:

• Agilent 1290 Infinity II LC system coupled to Agilent 6470 TQ LC/MS
• Poroshell 120 HILIC-Z column, 2.1 × 100 mm, 2.7 μm
• Mobile phases: 20 mM ammonium formate in water (pH 3) and water/acetonitrile (10/90)
• Gradient program delivering retention of paraquat at ~3.72 min
• MRM transitions: 171→77.1, 171→103.0, 171→155.0, 171→51.2 with optimized fragmentor and collision energies
• ESI-positive ionization, sheath gas 390 °C, capillary 3500 V

Key Results and Discussion

Linearity and calibration:

• Linear response from 5 to 200 ng/mL in milk matrix
• Regression coefficients (R2) > 0.9950 with 1/x weighting

Precision and accuracy:

• Spike recoveries between 97% and 112% across four concentration levels
• Repeatability RSD of 1.1% (n = 8) at 10 ng/mL

Chromatographic performance:

• Clear separation from matrix interferences, avoiding ion-pair reagents
• Retention time reproducibility ensures consistent quantitation

Advantages and Practical Applications

• Rapid and straightforward sample preparation suitable for high-throughput testing
• Simplified method by eliminating strong ion-pairing agents
• High sensitivity meets low regulatory limits for paraquat in dairy products
• Platform can be adopted by quality control and research laboratories for routine monitoring

Future Trends and Opportunities

The method could be extended to other food matrices such as juices and grains. Integrating automated sample preparation and online cleanup will increase throughput. Advances in high-resolution mass spectrometry and data processing algorithms could further enhance selectivity. Emerging regulatory guidelines may drive the demand for multiplexed pesticide residue screening.

Conclusion

A sensitive, selective, and reproducible LC/MS/MS method using HILIC-Z chromatography and MRM detection was developed for quantifying paraquat in milk. The approach simplifies sample preparation, achieves excellent recoveries, and meets stringent analytical performance criteria for routine residue analysis.

References

1. Paraquat, Diquat, and Mepiquat Analysis in Environmental Water. Agilent Technologies application note, 5994-1307EN, 2019.
2. Rapid Separation of Paraquat and Diquat Using HILIC with LC/MS Detection. Agilent application note, 5991-8830EN, 2017.
3. Comprehensive LC/MS/MS Workflow of Pesticide Residues in Food Using the Agilent 6470 TQ LC/MS System. Agilent application note, 5994-2370EN, 2020.
4. Bedi J. S. et al. Pesticide Residues in Milk and their Relationship with Pesticide Contamination of Feedstuffs in Punjab, India. J. Anim. Feed Sci. 2019, 27, 18–25.
5. Paraquat and Diquat Analysis in Tea. Agilent Technologies application note, 5994-1453EN, 2019.