Estimation of the uncertainties of extraction and clean-up steps in pesticide residue analysis of plant commodities

Abstract

Extraction and clean-up constitute important steps in pesticide residue analysis. For the correct interpretation of analytical results, uncertainties of extraction and clean-up steps should be taken into account when the combined uncertainty of the analytical result is estimated. In the scope of this study, uncertainties of extraction and clean-up steps were investigated by spiking ¹⁴C-labelled chlorpyrifos to analytical portions of tomato, orange, apple, green bean, cucumber, jackfruit, papaya and starfruit. After each step, replicate measurements were carried out with a liquid scintillation counter. Uncertainties in extraction and clean-up steps were estimated separately for every matrix and method combination by using within-laboratory reproducibility standard deviation and were characterised with the CV of recoveries. It was observed that the uncertainty of the ethyl acetate extraction step varied between 0.8% and 5.9%. The relative standard uncertainty of the clean-up step with dispersive SPE used in the method known as QuEChERS was estimated to be around 1.5% for tomato, apple and green beans. The highest variation of 4.8% was observed in cucumber. The uncertainty of the clean-up step with gel permeation chromatography ranged between 5.3% and 13.1%, and it was relatively higher than that obtained with the dispersive SPE method.

Keywords:

• ethyl acetate extraction
• extraction and clean-up
• gel permeation chromatography
• measurement uncertainty
• pesticide residues
• QuEChERS

Acknowledgements

The present study was performed in the FAO/IAEA Training and Reference Centre for Food and Pesticide Control, Austria. ¹⁴C-labelled chlorpyrifos was provided by Dow Chemicals. The support of FAO/IAEA in carrying out the study and the member of IAEA Agrochemical Units in Vienna and Dow Chemicals’ cooperation are greatly appreciated.