Liquid chromatography-tandem mass spectrometry method for simultaneous quantification of azoxystrobin and its metabolites, azoxystrobin free acid and 2-hydroxybenzonitrile, in greenhouse-grown lettuce

ABSTRACT

Lettuce is an important part of the diet in Europe. The permitted levels of pesticides in lettuce are strictly regulated and there is growing urge among food safety authorities to analyse pesticide metabolites as well. Azoxystrobin is one of pesticides that is frequently detected in lettuce. Although there are several analytical methods for the determination of azoxystrobin in lettuce, a sensitive method for the determination of its metabolites in lettuce is lacking. This study aimed at developing an extraction and LC-MS/MS method for the simultaneous determination of azoxystrobin, and its metabolites azoxystrobin free acid and 2-hydroxybenzonitrile in lettuce. Accelerated solvent extraction, QuEChERS extraction, and shaking extraction were compared using various solvents. The final method consisted of shaking freeze-dried sample in 0.1% formic acid in 80% aqueous acetonitrile. The selected method was validated by spiking each analyte at 125 ng/g and 500 ng/g. The method resulted in acceptable recovery for 2-hydroxybenzonitrile, azoxystrobin free acid, and azoxystrobin, with a RSD of <10%. The matrix-matched calibration curve for each analyte was linear over the range of quantification, with a correlation coefficient ≥0.98. The method was sensitive for the determination of 2-hydroxybenzonitrile, azoxystrobin free acid, and azoxystrobin, with limits of quantification of 0.36, 0.48, and 0.68 ng/g dry weight, respectively. The method was successfully applied to quantify 2-hydroxybenzonitrile, azoxystrobin free acid, and azoxystrobin in greenhouse-grown lettuce.

KEYWORDS:

• Azoxystrobin free acid
• 2-hydroxybenzonitrile
• pesticide metabolites
• quantification
• LC-MS/MS

Acknowledgements

Bente Laursen, Kirsten Heinrichson, and Elena Claudia Jensen are thanked for their assistance in the LC-MS laboratory. Steen Meier, AU, is thanked for helping to grow the lettuce in the greenhouse, and Senior Scientist Solvejg Kopp Mathiassen, AU, is thanked for spraying the lettuce with azoxystrobin.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was funded by a PhD grant (project no. 17638) from the Graduate School of Science and Technology of Aarhus University (GSST, AU); Aarhus University [17638].