High throughput residue analysis of paraquat and diquat involving hydrophilic interaction liquid chromatographic separation and mass spectrometric determination

ABSTRACT

A selective, sensitive and robust LC-MS/MS method is reported for the determination of the residues of paraquat and diquat in various fruit matrices, including grape, apple and pomegranate. The extraction with acidified water (0.1 M HCl) at 80°C (15 min) offered superior recoveries for both analytes with a significantly lower matrix effects as compared to the extraction with acidified methanol by the methods reported in the existing literature. The optimised HPLC conditions on hydrophilic interaction liquid chromatography (HILIC) columns, when coupled with electrospray ionisation-tandem mass spectrometry, offered their limit of quantification at 0.01 mg kg⁻¹. The analysis on an XBridge HILIC column required a thorough optimisation of the gradient programme to induce chromatographic separation and minimise matrix effects. This was not necessary when a CORTECS HILIC column was used, which provided selective and sensitive analysis within 5 min runtime using isocratic flow. Isotopically labelled internal standards corrected the recoveries of both analytes within 70–120% (RSD < 20%). For the first time, the applications of high resolution accurate mass analysis in the ‘time of flight – multiple reaction monitoring’ mode have been demonstrated as a complementary means of targeted screening of these compounds at 0.01 mg kg⁻¹ level. The method has a strong potential for applications in both official control and by those involved in food production for checking compliance with the EU MRLs.

GRAPHICAL ABSTRACT

KEYWORDS:

• Paraquat
• diquat
• LC-MS/MS
• QToF MS
• ToF-MRM
• fruits

Acknowledgements

The authors gratefully acknowledge funding support received from Agricultural and Processed Food Products Export Development Authority (APEDA), the Ministry of Commerce, Government of India. We extend our thankfulness to Simon Hird for his technical suggestions and honing the manuscript. Thanks are also due to Dimple Shah and Shrinivas Joshi from Waters for facilitating completion of this project. We also thank Suparna Banerjee for improving the overall presentation of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was supported by the Agricultural and Processed Food Products Export Development Authority (APEDA), the Ministry of Commerce, Government of India.