Abstract:

A fast method based on QuEChERS methodology was developed for the simultaneous determination of diquat, dimethoate, fenthion, fenthion-sulfoxide, fenthion-sulfone, haloxyfop-methyl in crude palm oil using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The clean-up effects of four dispersive sorbents were evaluated in terms of recoveries and matrix effects. The four sorbents were the mixture of primary secondary amine (PSA) and C18, a mixture of two sorbents a bonded C18 zirconia-coated silica (Z-Sep+) and C18, Z-Sep+, C18. As a result, the best effects were obtained from using the mixture of Z-Sep+ and C18 sorbents. The samples were extracted with methanol containing 1%(v/v) acetic acid. The extracts were cleaned up with dispersive solid phase extraction using Z-Sep+/C18 sorbents. Chromatographic analysis was carried out on an Atlantis T3 column with gradient elution. The pesticides were analyzed by positive electrospray ionization-tandem mass spectrometry under multiple reaction monitoring mode. The quantification was achieved using matrix-matched standard calibrations as external standard. The recoveries at the fortification levels of 10, 20 and 250 μg/kg in crude palm oil ranged from 70.0% to 97.9% with the relative standard deviations of 2.6%-10.2%. The limits of quantification (S/N≥10) were 0.1-2.5 μg/kg. The method has been proven to be simple, sensitive, accurate and environmental and thus suitable for the determination of the six pesticide residues above in crude palm oil.

Key words: crude palm oil, diquat, liquid chromatography-tandem mass spectrometry (LC-MS/MS), pesticide residues, QuEChERS, zirconium dioxide